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[
"Is it possible for a spatial body (e.g. planet, star) to have a perfectly smooth surface because of its gravitational pull?"
] |
[
false
] |
Or, Why is the Earth's gravitational pull too weak to prevent mountains?
|
[
"As I understand it it, not quite. If I recall correctly the largest ridges on a neutron star are approximately 5mm in height. Which is pretty damn small when you consider that these things are thousands of km in diameter. Comparatively smoother than a que ball."
] |
[
"Neutron stars have a radius between 10-20km, not thousands of km. ",
"http://www.astro.umd.edu/~miller/poster1.html"
] |
[
"Even the event horizon of a black hole, which is probably the smoothest object imaginable (probably because it's not an \"object\", but whatever), has distortions due to frame-dragging."
] |
[
"Why are Neanderthals considered a different species from humans if we could interbreed and produce fertile offspring?"
] |
[
false
] |
I've often heard the word species defined as the largest group of organisms that can interbreed and produce fertile offspring, if that is the case why do we consider Neanderthals a different species when many people today have Neanderthal ancestry?
|
[
"species are more about having a distinct gene pool with little or no outside interbreeding, and neanderthals had that for a long time and so developed a genetic distinction of their own, becoming a separate species.",
"basically they are a different species because they formed a isolated group that didn't interbreed extensively for a long time and therefor evolved differently from other humanoids. the fact we could still interbreed is irrelevant to them being a separate species or not.",
"the thing is, the term species isn't as clear cut as most people believe. what exactly the crossover point between being a separate species and not being one isn't based on clear easily identified criteria."
] |
[
"The thing is, there isn't one definition of \"species.\" The context in which you are using it is important. Consider asexually reproducing organisms like bacteria, how would one define species there if the case you used is the only one? ",
"/u/The_Countess",
" has the right of it here."
] |
[
"For some of the reasons that ",
"/u/ouemt",
" and ",
"/u/The_Countess",
" outline, the actual difference between species and sub-species is pretty irrelevant from a modern biological standpoint. Taxonomy is a great subject and very useful, but doesn't have as much weight in modern thinking of ancestry, sharing of genetic heritage or material, etc. Introgression, horizontal genetic transfer, and ecologically-based species concepts have all eroded the 'traditional' ",
", which encapsulates the notion outlined by OP that 'separate species don't interbreed.' ",
"A good peer-reviewed paper (de Queiroz, 2005) on why the traditional 'biological species concept' doesn't really hold much weight anymore ",
"is available for free from ",
". In particular, the notion that \"intrinsic reproductive isolation\" is either required or indicative of speciation is considered outdated. With the advent of modern genetics and molecular biology, it's become pretty clear that reproduction between what are undoubtedly separate species, and gene transfer between widely separated species (even between kingdoms), invalidate the traditional concept. It's still used, it's still even taught, but to me (this is definitely personal opinion), I put the BSC in the 'models of atoms' category of teaching science. ",
"What Pratchett fondly called \"lies to children\" type teaching of science privileges the teaching of simple, understandable models that are then explained in more detail later. The problem is that the simplified models (usually based on outdated scientific understanding) are usually all that most people get. Many people from my generation mistakenly think that electrons happily orbit nuclei in the same way the planets orbit the sun, because that is what they are taught. They either never understood (and who can blame them) or were never taught the statistical models of atomic structure used by many physicists today. In the same way, many people think \"separate species\" means two critters which can't successfully produce viable offspring, and bring up ligers, tigons, and mules as examples (because this is what we were taught in middle-school). The reality is far more complicated, of course! "
] |
[
"Is there an extreme point where the temperature decreases with pressure rather than increase (gas)?"
] |
[
false
] |
So, there's this: pV = nRT . From this is clear that if volume and number of molecules are constant, if we increase pressure the temperature has to increase. Is there a point when, if we increase the pressure to an immense threshold that there is actually a temperature drop because the molecules cannot almost move anymore?
|
[
"You have right intuition, but, as others have said already, it won't work like that for a classical gas.",
"See about ",
"negative temperature",
",\nif you have not a gas but a system of a kind with limited high energy states, by pumping enough energy into the system you could increase temperature from positive to plus infinity, where it wraps around to negative infinity, and continues to increase from negative infinity to a finite negative temperature.",
"Can't have that in classical gas, because energy of gas particles can increase without bound.",
"Negative temperature is still hotter then positive, though, meaning heat would flow from parts with negative temperature to positive temperature if they are in contact."
] |
[
"confining a particle, doesn't reduce its kinetic energy. If you confine the particle enough, its mean squared momentum (and hence mean kinetic energy) would increase with proportion to how small the confinement is. ",
"That's the result of the momentum being proportional to the inverse of the wavelength of the particle's wavefunction."
] |
[
"Negative temperature makes more sense if you think about 1/T (called thermodynamic beta) as the fundamental quantity instead of T (temperature). Then positive infinity is absolute cold, a point that can only be reached asymptotically. Small positive values are \"normal\" hot, and negative values are the weird \"hotter than hot\" that negative Kelvin represents, and the direction of heat flow makes sense.",
"It seems that 1/T may be a more physically fundamental value than T."
] |
[
"How viable is replacing/upgrading human parts with engineered ones at our current level of technology?"
] |
[
false
] |
Everything from prosthetic limbs to electromagnet "sensors" in the fingers. Please let me know if I should clarify more. AskAcademia didn't know much about the research of such things, so I thought I'd ask here.
|
[
"http://www.bbc.co.uk/news/science-environment-13273348",
"That is a story of a man who suffered nerve damage in his arm and lost use of his hand. The arm and hand were structurally fine, but the nerve damage couldn't be repaired so he elected to have his useless hand amputated in exchange for a robotic one that works."
] |
[
"If we could viably replace parts, why wouldn't we be doing so?",
"Except for where medically necessary, people tend to take that attitude of \"if it ain't broken, don't fix it\"."
] |
[
"Wow! The second video where he shows his hand rotate 360 degrees was crazy. "
] |
[
"If there was a hole in the perfect center of the earth (like ~7-8 ft diameter) and you were in it, how would gravity affect you?"
] |
[
false
] | null |
[
"You would be weightless."
] |
[
"At the very center, you would not feel any force.",
"This is a consequence of ",
"Gauss's law",
", which tell us that inside a spherical object with a mass we don't feel the attraction from parts of the object that are farther away from the center than you, and since you're at the center you will not feel anything.",
"If you have wiggle room (e.g. the hole is larger or you are in an empty tube passing through the center), you will oscillate around the center."
] |
[
"Inside a massive sphere the force depends linearly on the distance to the center.",
"Only if the sphere has a constant density. A reasonable approximation for the core of Earth, but not for Earth overall. If you would dig a tunnel through Earth the gravitational attraction would increase by a few percent until you reach the core."
] |
[
"Can a planet or moon move directly through a gas giant planet and survive?"
] |
[
false
] | null |
[
"I thought the laws of physics were universal (except in the neighborhood of a black hole or other singularities), and it would take a different universe to have different physics laws?",
"As for OPs question, we actually observed Schumacher-Levy crash on Jupiter in 1994. It definitely did not go through."
] |
[
"I thought the laws of physics were universal (except in the neighborhood of a black hole or other singularities), and it would take a different universe to have different physics laws?",
"As for OPs question, we actually observed Schumacher-Levy crash on Jupiter in 1994. It definitely did not go through."
] |
[
"Pass through, no. Successfully end up inside before being destroyed, maybe. I have not actually seen any literature on this but it may be possible for a moon to enter a puffy gas giant. ",
" ",
"Puffy gas giants, also known as super puffs, inflated hot jupiters, and various other names, have up to twice the radii of a regular gas giant. This means that their gravitational potential gradient, which is a measure of the stress across a nearby body would feel, is shallower (weaker/smaller). Given a rigid enough moon it might be possible for it to survive long enough to end up within the giant planet for a time before being destroyed.",
" ",
"It would not be too difficult to do a quick bit of crude estimates to determine the possibility. Simply use the crude definition of the ",
"Roche limit",
" and apply it to something like the Moon and an inflated hot jupiter from the (",
"NASA exoplanet archive",
"). A small bit of homework for someone since I am lazy!",
" ",
"The reason I mention this is that we have other cases of an object entering another. The observation of giant planets in short period orbits around white dwarfs may indicate some of these have survived within the envelope of the star. We also have the theoretical ",
"Thorne–Żytkow object",
" (as far as I am aware they have not been observed yet) which is where a neutron star enters into the envelope of a red giant."
] |
[
"Will sea level rise, and differences in where it occurs more greatly, have any effect on continental drift and plate tectonics due to shifting weight?"
] |
[
false
] | null |
[
"This makes sense intuitively but it's not quite right (or at least natural examples don't really bear this out). In general we expect that mountain ranges (and especially ones well described by a critical taper) will approach a steady-state where uplift balances erosion rates. So a sudden increase in precipitation may, for a relatively short time, lead to an increase in erosion rates when the landscape is still adjusted to less precipitation, but this will quickly (10",
" time scale) change as this excess erosion returns slopes to values in sync with the new discharge and original uplift rate. The largest effect to a mountain range would be contraction (i.e. in a volumetric or flux steady state, amount of material accreted in equals amount of erosion out, so more efficient erosion means less surface area is required to reach flux steady-state, hence contraction). So in a simple sense, increases in precipitation would lead to decrease in relief (more discharge means less slope required to balance uplift rate) and narrowing of mountain ranges, but those would be on 10",
" time scales. Also, a lot of that depends on how the climate changes, namely what's changing, mean precipitation? frequency or magnitude of rare events? frequency or magnitude of intermediate events? etc. These have the potential to greatly change the type of landscape (and erosion rate) response one would expect if climate changes."
] |
[
"According to ",
"data from NOAA",
", yes, it does. Also, ",
"this",
"."
] |
[
"There might be some planetary-scale impacts, but I'd look more into things like changes in erosion speed, which would have effects on the state of critical taper in active mountain ranges and interplate sismicity and sedimentary rates along convergent margins.",
"In other words: mountain chains erode faster from changes in rain patterns. This changes their weight distribution profile, which readjusts more frequently to get back to stability. And more wet sediment piles on top of subducting plates through accelerated erosion, which might affect the volumes of magma formed through crustal recycling along Andean-type margins as this material goes under the mountain range down the subduction zone and partial melting. Might be more volatiles in the magma as well (all that water in the sediment), which might make for more explosive volcanism.",
"But such effects would take a while to manifest themselves."
] |
[
"If something is lifted by a magnet and the magnet is moved away with the same velocity, will the object and magnet remain at a constant distance apart?"
] |
[
false
] |
[deleted]
|
[
"you'd have to move the magnet ever faster away: If they're moving at the same velocity, they're at rest (with respect to each other). If they're at rest, the object is attracted to the magnet and begins to accelerate toward it. Therefore the magnet must move more quickly away from the object. So unless you're planning on accelerating the magnet for literally forever, yes, the object will catch up to it."
] |
[
"As for your proposed idea, you could think of it kind of like a necklace going around the moon with beads every so often. You could push on one bead, and it'd push on the other beads all the way around, and they'd travel around together, but you'd have to push just as hard on that first car as you'd have to push on all the cars together.. in which case, why muck about with magnets, and why not just attach each car to each other with a cable? Maybe still magnetically levitate them to reduce friciton, but otherwise, it's the same thing, more or less."
] |
[
"magnetic force inversely proportional to the distance between the magnet and object",
"It's proportional to the ",
" of the distance. In the scenario you describe the single carriage would then no longer be balanced by the attraction of the carriage behind it (which was now weaker) and it would snap forward. It can't pull harder on a carriage behind it if the distance becomes greater. That doesn't make sense even with it being inversely (and not inverse square) proportional."
] |
[
"How does the wind carry sound?"
] |
[
false
] | null |
[
"OP, do you mean how does sound propagate in air? Or how does wind affect sound propagation?",
"I'm going to go out on a limb and guess you mean the latter, in which case, a wind front traveling with a constant speed will just make the wave propagate at 343 m/s (speed of sound in still air) + speed of wind for a non-moving observer (vector addition)."
] |
[
"shockwave",
"Shockwave has a specific meaning in acoustics. So, let's replace \"shockwave\" with \"pressure disturbance\".",
"Slightly more nitpicky (sorry!), I would also say that acoustic waves don't propagate from particle to particle, just because that makes it seem like it's a phenomenon that's primarily occurring at an atomic level. Pressure wave propagation in gasses (acoustic waves) have more to do with the space between particles, or really groups of particles. It's more of a macroscopic effect than the phrase \"particle to particle\" would imply."
] |
[
"shockwave",
"Shockwave has a specific meaning in acoustics. So, let's replace \"shockwave\" with \"pressure disturbance\".",
"Slightly more nitpicky (sorry!), I would also say that acoustic waves don't propagate from particle to particle, just because that makes it seem like it's a phenomenon that's primarily occurring at an atomic level. Pressure wave propagation in gasses (acoustic waves) have more to do with the space between particles, or really groups of particles. It's more of a macroscopic effect than the phrase \"particle to particle\" would imply."
] |
[
"How come when we walk, our arms remain straight, remaining down. But when we run, we automatically bend our elbows?"
] |
[
false
] |
And why is bending the elbows 90 or so degree more comfortable than keeping them straight?
|
[
"When you walk or run your arms act as pendulums to counterbalance the movements in your torso as your legs propel you.",
"A pendulum naturally swings at a fixed speed determined by it's length. By shortening the length of your arms you enable the pendulum to swing faster to better match your stride."
] |
[
"In order to correctly counterbalance the motion of your legs, the movement of your arms doesn't need to match your movement speed, it needs to match the timing of the events in your gait. When you are driving forward off of your back foot your front arm helps to carry momentum forward. When your arm reverses direction at the top of the arc it acts as a brake on the motion to allow your foot to come forward.",
"It is true that your arms are not passively swinging. The swing is controlled to some degree to make sure that the correct timing results, regardless of whether the particular pendular motion is mathematically 'natural.' It is also true that the same timing can be accomplished without changing the length of the pendulum by simply inputting muscular energy to control the movement of the pendulum, so to some degree the motion does probably arise from secondary constraints such as stress placed on the elbow. But there are direct benefits to a shorter pendular motion such as requiring less energy creating less torque in the torso."
] |
[
"What",
"Your arms aren't just swinging freely when you run, and you can run at different speeds without changing the angle of your elbow. If we're pulling guesses completely out of our asses, I'd say maybe walking your arm movement is somewhat incidental (where they probably do just swing freely), but when you're running you bend em so they aren't jangling around, causing stress on your elbow."
] |
[
"Is it possible to genetically determine in young age if somebody is likely to become a criminal?"
] |
[
false
] |
[deleted]
|
[
"Lazy criminology student here.",
"There are two main criminal theories in the field of Criminology; Positivism and Classicism.\nAccording to Cesare Lombroso, an Italian positivist, you could differentiate a criminal to a regular civilian only by looking at his facial and body structure. Almost all of his findings have been discredited to this day, clearly.\nClassicism explains that anyone can commit crime, and therefore become a criminal, given that the benefits of the crime outweigh the risk of getting caught. Therefore, anyone can commit a crime, depending on the situation.",
"Nowadays, positivism has adapted itself well to our culture, and focuses more on environmental factors (neighborhoods) when anticipating the likelihood of someone to commit crime. ",
"Positivism, as you can imagine, has a lot of criticism. Despite having sound arguments in its theory, it's filled with views that can easily become discriminatory. Especially in today's more \"liberal\" culture."
] |
[
"I wholeheartedly agree with this answer. But there was an interesting study published last year in the journal ",
" entitled ",
"Examining the genetic underpinnings to Moffitt's developmental taxonomy: a behavioral genetic analysis",
". In this the authors found 56-70% of factors leading to being classified as \"a life-course persistant offender\" could have a genetic cause. ",
"Science Daily",
" provided a summary of the article. I don't know this field well, or articles that might dispute this. I'm putting it here as food for thought.",
"Given our current inability to find genes responsible for most of the predicted genetic variation for several traits (including height), I think it is ",
" that we will be able to screen for these complex behavior traits any time soon. And even if we do, remember that genetic predisposition is just that; our choices (and chance) affect our outcomes."
] |
[
"If your definition of criminal is based on commission of crimes, then I would say it is vastly unlikely since almost everybody is a criminal whether they are aware of it or not., and those who are not criminals will mostly be so due to luck.",
"If you restrict the definition to those who knowingly break a law that their community considers \"serious\" by whatever criteria, then it might be possible to correlate certain genetic markers with higher likelihood of being a criminal, depending of course on that very community standard. However, given any sort of correlation between certain genetic markers and certain criminal behaviors, you will almost certainly be able to redefine \"criminal\" so that the answer to your question is yes or no."
] |
[
"is the energy that life uses different from other types of energy such as light or heat?"
] |
[
false
] | null |
[
"i'm not quite sure at what you're getting at, but the base of all life is light energy: light is turned into chemical energy through photosynthesis, the chemical energy then travels up the food chain to eventually reach us\nfor example: Phytoplankton (converts light to chemical energy) -> zooplankton -> small zooplankton feeding fish -> larger oceanic fish -> us.\nSo really, ",
" all life is dependant on light energy from the sun. Some exceptions are chemeosynthetic bacteria which use energy from reducing sulphide and other chemical compounds to create organic compounds. "
] |
[
"If you're thinking of a concept such as a \"life force\" or something similar, then that is absolute nonsense. Your body runs on chemical energy that is no different than the chemical energy in gasoline, for example."
] |
[
"It should be noted that there are other forms of energy that life uses, like electrochemical gradients."
] |
[
"Does being in an extended coma have any impact on the way the body ages?"
] |
[
false
] |
If you were in a coma for ten years, do we have any way of knowing whether you would look relatively older, younger, or about the same as you would if you hadn't been in the coma?
|
[
"I treat comatose patients for a living.",
"The answer depends on the age at which one enters a coma.",
"When kids become comatose or vegetative, their bodies still grow, albeit at a reduced rate since it is hard to keep them fully nourished and they often have endocrine problems, depending on how they were injured. Because they are not using their bodies, not only do the muscles atrophy, but the bones do not grow normally either. Feet can become rounded because they never bear weight. Legs can become curved for the same reasons, plus bone density suffers in non-load-bearing regions. Muscle contractures frequently develop and can lead to contorted limbs. Scoliosis is also common for these same reasons. Many vegetative children enter puberty early due to the hormonal abnormalities. Their faces often become rounded with time since they are not using the facial or chewing muscles.",
"Adults who become comatose are not affected quite as badly but are still prone to many of these issues. They don't get facial wrinkles because they don't use many expressions and they don't get sun exposure. The skin often becomes not just pale, but waxy. They still grow hair and need their faces shaved (men).",
"The end result is that many people, after a few years in a coma, can be almost unrecognizeable when compared to old photos of themselves. Just yesterday a mom was showing me a photo of her kid from a year ago before a catastrophic brain injury and it was hard to tell they are the same human being."
] |
[
"As far as looks go, that's an interesting question. I would imagine the average person would look slightly younger because there'd be no sun damage or smoking wrinkles. Also decreased facial expressions could play a role. The masseter might be smaller from no chewing which could attribute to the emaciated look; I'm not sure how this affects aging. Also consider psychological stress; there's a reason Obama looks much older now (aside from 8 years having passed). I think the comatose patient would have less factors affecting their appearance.",
"\nAs far as internal body processes that do not directly affect appearance, there's definitely many variables (particularly which parts of the brain are damaged) but:",
"\nLying prone lowers blood pressure and decreases the workload of the heart. Metabolic damage is key in determining lifespans (think stroke or heart attack).",
"\nNutritionally they'd be on tube feedings so their needs would be adequately met. This helps fight against obesity.",
"\nAside from pressure ulcers (which are largely preventative) I'm having trouble finding ways that someone who is bedbound would be worse off from a health standpoint. The risk of trauma and degenerative musculoskeletal disorders would be reduced. "
] |
[
"So sad. A friend of mine who is a couple years younger (He's 18) had a traumatic brain injury one year ago and most of what you described has happened to him "
] |
[
"Why is belly fat different from other fat?"
] |
[
true
] |
[deleted]
|
[
"abdominal fat is more correlated with insulin resistance. We don't know if the belly fat causes insulin resistance or if insulin resistance makes you more likely to store belly fat. ",
"http://diabetes.diabetesjournals.org/content/45/5/633.short"
] |
[
"There are studies linking stomach fat and health problems."
] |
[
"Additionally, your body \"likes\" to store fat around the belly, buttocks, and hips. This is because your torso moves the least. Think about it - if all your belly fat was instead located in your fingertips, it would take a lot more energy to move your hand around with the extra weight on it, as your arms and legs move quite often. Since your torso moves the least in comparison to your limbs, it is much more efficient for your body to store excess weight there."
] |
[
"In space could a planet orbiting a star orbit faster than another planet with a closer orbit to the same star?"
] |
[
false
] |
I'm currently replaying Mass Effect and clicking on planets in systems when something that caught my interest in the planetary details. I'm in a 6 planet system and the orbital periods for the planets are as such Planet 1: 0.1 Earth years Planet 2: 7.8 Earth years Planet 3: 20.4 Earth years Planet 4: 1.1 Earth years Planet 5: 37.5 Earth years Planet 6: 90.5 Earth years Everything is typical regarding orbits getting longer the further away a planet is from its home star except for planet 4. I'm wondering if this is just an error or if it could be scientifically possible. It defies everything I know about orbital mechanics and escape velocities. Theoretically the planet should have an orbital period of 28ish Earth years. I would assume that if it had the horizontal velocity needed to achieve such a fast orbit that it would just break away from the stars gravity
|
[
"Probably a typo and it should be 31.1 years. The scenario as described is impossible."
] |
[
"For circular orbits:",
"a - acceleration due to gravity",
"v - orbital speed",
"r - distance from center of gravitational body",
"t - orbital period",
"k - constant in gravitational equation, equal to the gravitational constant multiplied by the mass of the body.",
"a = v",
" / r, alternatively v = sqrt(a * r)",
"t = 2 * pi * r / v",
"a = k / r",
"Substituting equation 1 into equation 2:",
"t = 2 * pi * r / sqrt(a * r)",
"Substituting equation 3 for a:",
"t = 2 * pi * r / sqrt(k / r) = 2 * pi * r",
" / sqrt(k)",
"Since k is a constant, the orbital period of a circular orbit around a given mass is a function of only the distance, and it increases with increasing distance. So if these are circular orbits it is not possible."
] |
[
"I agree that it is not possible, but circular orbits are kind of rare, especially as you get farther away from the parent star."
] |
[
"Do points on the equator always have 12 hours of sunlight and 12 hours of darkness?"
] |
[
false
] |
[deleted]
|
[
"A graphical answer.",
"Also just pretty interesting."
] |
[
"The day is slightly longer than 12 hours at the equator because the sun is refracted through the atmosphere, causing it to appear higher in the sky than it would without an atmosphere. The other main reason the day is slightly longer than 12 hours at the equator is that we define a day as when the first part of the sun rises to the last part of the sun sets, not when the middle of the sun rises and sets.",
"The amount of daylight at the equator does not change much between seasons.",
"Edit: ",
"Source",
"...good old wiki"
] |
[
"Bonus fun fact:",
"The angle of refraction through the atmosphere is such so that the visible offset of the sun against the horizon is roughly the same as its diameter.",
"When you ",
" the sun just touching the horizon is about the moment it ",
" actually below the horizon."
] |
[
"Will using bigger, external antennas improve signal reception on smartphones?"
] |
[
false
] |
15 years back, all cellphones used to have an extensible antenna you had to pull out whenever you wanted to speak. Then the Nokias started coming out which just had a "bud" antenna that extended an inch out of the phone. Then all phones started having internal antennas. My question is, have we sacrificed on the signal strength (while maybe cell towers became more powerful) to put the antennas inside the phone, or did we innovate a new type of antenna to be able to put it inside the phone and get the same reception. As a corollary, could we build a smartphone with an external antenna that would have a much better signal strength compared to a regular smartphone in the same location?
|
[
"The size of the antenna is directly proportional to the wavelength it provides gain for. So it really depends on the wavelength/frequency you are trying to pick up. The higher the frequency, the smaller the antenna, in general. The right external antenna will certainly improve your signal strength.",
"cell phones operate at a high enough frequency and manage to separate signal from noise so well that they have made external antennas largely unnecessary. And to answer your question, it's a bit of both, better antennas, stronger/more cell tower coverage."
] |
[
"The internal ones are the hardest to design because of space constraints. External MIMO ones are more difficult to design than the old pull-out whips which OP mentioned. "
] |
[
"All true. ",
"Also, we require our phones to operate in any position, on multiple bands, and resist multipath cancellation. A simple 1/4 wave whip with ground plane isn't enough anymore. ",
"MIMO",
" antennas are used which would be very difficult to reproduce externally without lots of simulation and testing. "
] |
[
"If high temperature rock essentially condenses into glass, why is the surface of the earth made of rock not glass?"
] |
[
false
] | null |
[
"Igneous rocks are divided into two groups: volcanic (or extrusive) and plutonic (or intrusive). There are examples of rocks made of glass, e.g. obsidian. These are volcanic rocks that are formed when lava is quenched rapidly; in fact, too rapidly for crystals to form into an orderly lattice structure. But plutonic rocks are formed underground from magma, where it can cool down and solidify at a much slower rate, allowing time for crystals to grow. Basically, the \"non-glass\" igneous rocks on the surface of the Earth are from these plutonic origins."
] |
[
"Sand is (often) composed of quartz, which differs from glass and amorphous silica in having a definite crystal structure. In glass, the silicon and oxygen atoms are more or less randomly arranged."
] |
[
"The overwhelming majority of rocks present at the surface were not formed there but at depth, either through metamorphism, intrusion or diagenesis and subsequently brought to the surface through tectonic processes and erosion. Those rocks are generally at desequilibrium relative to surface conditions.",
"The \"world of glass\" scenario you evoque does indeed apply to some rocks formed at the surface through cooling such as through the cooling of lava near to volcanic centers. Rocks derived from lava contain an abundant fraction of volcanic glass, such as hyaloclastic material and clinker, provided the lava cools extremely fast (eg: water quenching). Slower cooling will allow the growth of some crystalline material."
] |
[
"What is the heaviest element that is safe to handle or carry around all of the time?"
] |
[
false
] |
I was watching videos and they mentioned that Osmium was the heaviest element. I looked it up and it seems that it wouldn't be safe to carry it around in your pocket. What is the heaviest element that a person could handle and carry around safely?
|
[
"As Fabien said, iridium is the heaviest thing you could carry around fairly safely. However, it's reasonably expensive and hard to find as jewelery (I extrapolated you asking about carrying around all the time to being a piece of jewelery). If you're after something you could get a ring or chain made of fairly easily, platinum would be a good bet, easier to find and a good sight cheaper than iridium, while being very close in density.",
"At their respective densities:\n"
] |
[
"Where did you get those density values? Wikipedia and WolframAlpha both show 22.59 for Osmium and 22.56 for Iridium."
] |
[
"Old textbook... It's one of my dad's, from the 70s, probably wrong. Will defer to your values"
] |
[
"Can electric propulsion be used to launch rockets into space?"
] |
[
false
] |
I've been looking at the differences between chemical engines and electric propulsion (EP) engines for rockets. Whilst the EP engines work well in space they don't seem to have enough thrust to launch a rocket into space and completely replace chemical engines. Does anyone know if this has been done or could possibly be done with the technology we have now?
|
[
"Not really! Not yet, at least.",
"The idea with EP engines or things like ion thrusters is that they give a small amount of thrust, but they do it very efficiently, so you can keep on thrusting for a very long time. If you're in space, this all adds up over time, and you can end up going very fast with very little fuel, or none at all.",
"However, to get out of the atmosphere and reach orbit, you need a large amount of thrust in a very small amount of time. Currently, this seems to only be possible by a large chemical (or even nuclear!) reaction or explosion that releases a large amount of energy really quickly, giving you a lot of speed really fast, but at a large cost in fuel."
] |
[
"I know. I personally hope it's greater than zero thrust. science paradigm shifts are exciting.",
"In my reply I wanted to emphasize the huge gap between what the drive might potentially generate and the force required to launch something from Earth."
] |
[
"The EM drive that was tested by NASA has been reported to produce something in the order of micronewtons, so we need to improve it by a factor of billions before it could ever be used to launch something.",
"Assuming that number means anything. In that NASA paper, they didn't quantify any systematic errors. So their number could easily be consistent with zero thrust."
] |
[
"I picked up this lab apparatus at an estate sale, can anyone tell me what it's used for?"
] |
[
false
] | null |
[
"Looks like something used to purify water, but I could be wrong. If you can't get it spotless with acetone, strong acid, or other powerful cleaner, you won't be able to sell it. "
] |
[
"looks like a soxhelet extractor"
] |
[
"http://en.m.wikipedia.org/wiki/Soxhlet_extractor"
] |
[
"Are there tides underground?"
] |
[
false
] |
Do tides effect underground lakes or groundwater? What about magma chambers?
|
[
"Have a read of ",
"this report, especially the graphs on page 13 and 14",
". It shows how the tides ",
"affect",
" the water level underground. Essentially with underground wells and groundwater, the water level moves up and down in cycles in much the same way as other large bodies of water like the sea.",
"This paper on underground aquifers",
" made a similar conclusion, stating in part: \"a deep well in an unconfined crystalline rock aquifer ... shows a cyclic fluctuation in the water levels ... fluctuations [of water level] have considerably high correlation with earth tides\"",
"Incidentally (this is slightly off topic) but the entire body of the earth is affected by tides, not just the water. This is ",
"known as an earth tide",
", and can be caused by the sun as well as the moon."
] |
[
"With respect to tides caused by the Sun. Counterintuitively, even though the Sun's gravitational force on the Earth is closing in on 200 times that of the moon, the tides are nearly undetectable by comparison. This is because the tides are caused by a gravitational differential from near side to far side of the Earth by the mass in question. The Moon's differential is much higher when compared to the Sun's. "
] |
[
"The ratio of the mean distance to the sun to the mean distance to the moon is about 390.",
"The ratio of the mass of the sun to the mass of the moon is 27 million.",
"Thus the ratio of the tidal forces (which is given by the ratio of the masses divided by the cube of the ratio of the distances) is about one half.",
"Solar tides are far from undetectable; in fact they are very important. They are the reason that ",
"spring tides",
" are so much larger than neap tides. In many places if you chart the tides over the course of a month, it is quite easy to see the destructive and constructive interference between lunar and solar tides."
] |
[
"Is it really bad for the body to eat Food with flavour enhancers like Monosodium Glutamate?"
] |
[
false
] | null |
[
"Monosodium glutamate (MSG)",
", is merely the monosodium (one Na+) salt of the amino acid, ",
"glutamic acid",
". Glutamic acid is one of the 20 amino acids that make-up all the proteins within your body, alongside being a key neurotransmitter (sending messages between neurons) in the nervous system. When MSG enters your mouth and dissolves in your saliva/gastrointestinal tract, the sodium (Na+) ion dissociates. Thus, you are essentially just eating salt (minus the Cl- ions) and glutamic acid (a perfectly 'natural' substance). ",
"I believe the reported problems associated with MSG consumption (headaches, stomach ache, etc.; although only correlations and may not be caused by MSG) are more due to the fact you're consuming a high concentration of glutamate in a short space of time. Furthermore, as far as I know, it is thought that some people may present a slight intolerance to glutamate (exacerbated by eating foods rich in glutamate, in high quantities - chicken, tomatoes, [some] asian food, etc.)"
] |
[
"It's BS. Some people with glutamate sensitivities can get headaches from over-consumption of it, which may have contributed to people believing the ridiculous 'brain cell loss' talk."
] |
[
"Exactly- MSG is a primary amino salt, and a direct trigger of the umami taste (savory) in your tastebuds. This is the same as NaCl with your \"salty\" taste trigger.",
"For this reason it gets loaded into junk food to render savory flavor.",
"It is in itself harmless, but gets applied poorly, thus the bad name. The reason why humans like the taste, and have umami as one of our 5 primary groups is that amino acids are critical to our survival."
] |
[
"Is there any scientific data to suggest barometric pressure can cause physical affects like headaches or increased arthritic pain?"
] |
[
false
] |
This is such an incredibly common and everyday accepted thought, at least in my part of north america. Are there any studies to back this up? I couldn't find much.
|
[
"http://www.ncbi.nlm.nih.gov/pubmed/21921370",
"CONCLUSION: Barometric pressure change can be one of the exacerbating factors of migraine headaches."
] |
[
"Please everyone, do not post your anecdotal experience here. This is looking for a specific mechanism, not your personal experiences. Thanks. "
] |
[
"Isn't that more to do with being on the safe side to avoid going into labour during the chaos/cleanup of the hurricane though?"
] |
[
"What is future of instruments that depend on superconducting magnets, given the possibility of a helium shortage in the future?"
] |
[
false
] | null |
[
"The notion of a helium shortage is very overblown.",
"Helium is a by product of natrual gas production. The US used to stockpile helium for Cold War purposes. They liquidated the stockpile, which lowered prices to the point it wasn't profitable to collect it anymore. ",
"So now the stockpile is liquidated, and the helium extraction industry hasn't ramped up yet, so we are looking at ",
" shortages. As it gets more expensive, more people will collect it from natural gas, and the price will stabilize a new higher level.",
"Helium is not going to become \"extremely rare\" anytime soon. "
] |
[
"Helium isn't going away any time soon but it is getting more expensive.",
"People are simply going to want to switch to recycling helium (before they would liquefy it once then let it boil off to atmosphere). Once you set up a recycling system, one `charge' of helium ends up being a small part of the price."
] |
[
"So then, with helium eventually going to be costly, what is the future of instruments that depend on superconducting magnets?"
] |
[
"Why are people predominantly right handed?"
] |
[
false
] | null |
[
"There are many theories, but the prevailing current research indicates that handedness, and specifically right-handedness, is a trait that can be attributed to tool use, and is likely inherited from a common ape ancestor. ",
"Several recent studies put forth the theory that the hand used to interact with the world depends on the animacy of the object in question. For instance, children (as well as apes, for that matter), predominantly utilize their left hands when communicating and interacting with another human or live animal. However, when presented with an inanimate object that can be used as a tool, they primarily utilize their right hands. ",
"http://www.ncbi.nlm.nih.gov/pubmed/23022751",
"http://www.ncbi.nlm.nih.gov/pubmed/22829099"
] |
[
"But why right? Like why can't I just switch the words \"left\" and \"right\" in your answer."
] |
[
"I'd like to see your sources for that left brain, right brain stuff."
] |
[
"Is taking rabies vaccine 100% effective? as in the once infected person won't need a booster shot in the future?"
] |
[
false
] |
Suppose a patient is given the treatment for rabies after getting bitten and then gets cured after a while. Are there any chances the infection might still stay active somewhere in the body for years? Are the booster doses needed? Is there any scenario where the cured person still has a possibility to get infected after many years from the past supposedly cured infection if booster shot isn't taken? Can the infection stay passive in the patient even after the treatment? There's a lot of conflicting information out there. I would appreciate some explanation on this.
|
[
"You're supposed to get a titer every couple years to check your levels of protection and if those levels drop you would require a booster. I have friends that work with bats and other wildlife and haven't heard of them needing boosters over many years but I'm sure it happens."
] |
[
"Typically every ",
"2yrs",
" for titers.",
"The only problem? No one knows what titers specifically are protective; the \"less than\" level requiring a booster is somewhat arbitrary. ",
"For obvious reasons, the experiments necessary to determine the appropriate level - exposing people with varying antibody titers to rabies - have never been done :)",
"Source - I've gone through full post-exposure prophylaxis. There's no concern for developing rabies further down the road and boosters are only necessary for those who continue to be at high risk for exposure."
] |
[
"If you have a bite or a suspected bite, you get two things on the first day. You get your first dose of vaccine as well as a weight based Immunoglobulin (Ig). Vaccines take time to work, and so to keep you from death the Ig is basically premade antibodies that will work to fight rabies immediately. ",
"So Day 0 you get those and then you typically get boosters on Days 3, 7, and 14. ",
"As others commented I think there has been like 1 rabies infected person who lived without treatment. That’s why bite or suspected bite or even remote possibility of exposure, get Ig and vaccine. If you wake up to a bat in your room, assume exposure. ",
"By then you should be protected for about 3 years. If you work around bats you’ll get boosters after that point to help ensure you have circulating antibodies. ",
"Source: I’m a doctor and I woke up to a bat in my room two years ago so I assumed exposure. And I’m alive still."
] |
[
"This might be a stupid question. With rising sea levels, can't we just dig dirt from the ocean floor to make it \"deeper\"?"
] |
[
false
] |
They say over a long period of time coastal cities will disappear, but wouldn't taking dirt out of the bottom of the ocean allow it to hold more water?
|
[
"This is the type of question where simple, back of the envelope calculations can be useful. It is important to realize just how big ",
"ocean is",
", with a surface area ~361 million km",
". Even if we ignore the complication that at an average depth of ~3700 m (and many places significantly deeper), consistently removing even a small layer of material from the oceans would be basically impossible, we need to consider the volume of material we would need to remove if it was possible. The current rate of sea level rise is ~3 mm/yr and depending on the projection, by 2100, the amount of total sea level rise will be 0.25-2 meters. Factoring in the surface area of the ocean, if we were removing 3 mm of material uniformly from the bottom of the ocean per year (to keep up with the current rate of sea level rise), that would be a volume of material of 1.08 x 10",
" m",
" of material. To put that in perspective, if you spread that volume of material out over the entire area of the US (including Alaska, and using ",
"9.826 million km",
"), that would be a 110 cm thick layer of material. If we instead wanted to remove enough material to keep up with an average total sea level rise by 2100, say 1 meter, that would be 3.61 x 10",
" m",
" or using the US example, a layer of material ~36.5 meters thick covering the entire US. In short, even sidestepping the problems of how one would remove that volume of material at the depths involved, there is no where to put that volume of material."
] |
[
"Aside from the physics issues, there is so much life on the ocean floor that it would likely be ecologically disastrous. Many are endemic, undiscovered, endangered, or all of the above. ",
"There are also many other ecological problems caused by climate change in addition to rising sea levels, so addressing the issue at the source is better in every way."
] |
[
"It's almost liks you'd need to cause an entire global industry's worth of disruption to cover this single symptom of a certain globla industry's activities."
] |
[
"Have we found any ways to make a neural network or other ML algorithm tell us \"why\" it came up with its decision?"
] |
[
false
] |
I know that's a big issue with ML systems, that their algorithm is completely illegible by humans. It finds a pattern and produces an answer, but besides the neuron weights we don't know how it defines the pattern or produces the answer. Have we found any way of extracting a more human-legible reasoning system from trained ML models?
|
[
"Not to be overly critical but most of what you said is not accurate. It's a little much to type out on my phone, but your first point about NNs lacking reasoning is spot on - the power of machine learning comes from learned relationships instead of designed heuristics.",
"However, it is unfair to say that networks are black boxes and are abstract. We have found that specific network architecture is better suited for specific tasks, ie an RNN vs a CNN. In these contexts, network weights have meaning and can be human interpretable. For example, networks trained for patch-based compression will create filter banks that resemble human designed approaches (ex. 2D DCT)."
] |
[
"Not to be overly critical but most of what you said is not accurate. It's a little much to type out on my phone, but your first point about NNs lacking reasoning is spot on - the power of machine learning comes from learned relationships instead of designed heuristics.",
"However, it is unfair to say that networks are black boxes and are abstract. We have found that specific network architecture is better suited for specific tasks, ie an RNN vs a CNN. In these contexts, network weights have meaning and can be human interpretable. For example, networks trained for patch-based compression will create filter banks that resemble human designed approaches (ex. 2D DCT)."
] |
[
"I didn't really mean to say they're black boxes. My point was that after we structure the network and determine how it's trained, there's no longer abstract intention that goes into it, and therefore its behavior is blind.",
"We can determine what relationships it's focusing on through analysis, and we can even make it predict an input for a given output, but just as you said, there's no reasoning behind it. That's what I meant by \"what\" vs \"why.\"",
"EDIT: Also, my point about abstractness was that modern neural networks aren't capable of abstract reasoning, and that we would need AI that is capable of it to answer a \"why\" question."
] |
[
"Would this be an hypothetical action/example considered “faster than light”?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"You question is either commonly occurring or has been recently posted on ",
"/r/AskScience",
". It may also be answerable using a Google or Wikipedia search.",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"hey there!",
"Please cite where this has been asked before."
] |
[
"You can find answers in our ",
"physics FAQ",
". In particular ",
"this link."
] |
[
"What are the biggest problmes people would enconter living in Mars 3.6 m/s² gravity?"
] |
[
false
] | null |
[
"We don't know for certain.",
"What we do know is that living in microgravity affects the immune system, and it causes bone mass and muscle mass loss. This is under active reasearch, especially in the ISS.",
"http://www.nasa.gov/content/study-reveals-immune-system-is-dazed-and-confused-during-spaceflight/",
"But we (still) don't have enough studies to conclude if 1/3 g would be enough to prevent these problems.",
"Bone mass and muscle mass loss are ",
" easy to handle with exercises that mimic gravity, but still a long time of recovery is needed.",
"http://science.nasa.gov/science-news/science-at-nasa/2001/ast02aug_1/"
] |
[
"well 50kg on earth would be a lot heavier then 50kg on mars because of the 1/3 gravity, so what im wondering is would the muscle mass loss cancel out the fact that everything would weigh less? yes, you would loose muscle mass, but at the same time everything would weigh less. i am genuinely curious, so if someone that knows what their talking about could step in, it would be appreciated."
] |
[
"well 50kg on earth would be a lot heavier then 50kg on mars because of the 1/3 gravity, so what im wondering is would the muscle mass loss cancel out the fact that everything would weigh less? yes, you would loose muscle mass, but at the same time everything would weigh less. i am genuinely curious, so if someone that knows what their talking about could step in, it would be appreciated."
] |
[
"Do we naturally think in Base 10 (with 10 numbers!) or is it a cultural influence?"
] |
[
false
] | null |
[
"Other cultures have had different number systems. ",
"The Babylonians had a base-60 system",
", for example.",
"Also, the Roman system didn't have zero, so it didn't have a base per se. Just symbols for different values. It made arithmetic very hard. The number system we use now is ",
"the Arabic system",
"."
] |
[
"It's ",
" \"natural\" or \"the most natural\", though. There are plenty of other body counting systems. ",
"Some cultures touch each joint of the fingers with the thumb, letting you count up to 12 on one hand.",
"The ",
"Foe count not just the fingers, but all the way up to the top of the head and then back down to the other hand",
", going from 1 to 37.",
"Even in among \"Western\" cultures, there can be a lot of variation between individuals even in \"normal\" finger counting. See ",
"Pika et al. (2009)",
".",
" Here's ",
"a listing of many different numeral systems",
" used in about 4,000 out of the 7,000 or so extant languages."
] |
[
"I believe it's been demonstrated (through interactions with modern pre-mathematics societies) that humans naturally think in a logarithmic base, and can only naturally (\"instinctually\") identify rough halfs/doubles of given values.",
"I'll try to find a citation.",
"As for your other questions, plenty of advanced societies used differing number systems. Already mentioned are Babylonians and Romans. Ancient South-American civilizations used mixtures of base-60 and base-13, as well. Ancient Chinese used base-1 for some things."
] |
[
"Is the lack of hair on our bodies for the purpose of keeping us warm a way we physically adapted to our technology i.e. clothes?"
] |
[
false
] | null |
[
"No. ",
"source"
] |
[
"From the article:",
"Loss of fur was an adaptation to changing environmental conditions that forced our ancestors to travel longer distances for food and water.",
"Analyses of fossils and genes hint at when this transformation occurred.",
"The evolution of hairlessness helped to set the stage for the emergence of large brains and symbolic thought."
] |
[
"Ah, the famous Clinging Garbage Theory. Sounds like solid science to me."
] |
[
"What is the physiological mechanism through which fatigue/tiredness can cause visual/auditory anomalies?"
] |
[
false
] |
I'm a very fatigued medical student studying not-neuro right now, but I always notice these little visual anomalies when I am very tired. Like when I stare at words on a computer screen, they will start to ripple, or I'll see color start to materialize on a white screen. (I know I need sleep, thank you) I'm curious how fatigue produces this. I have heard that extreme exhaustion will cause visual/auditory hallucinations, but never figured out the mechanism. What kind of "wires" are crossing to form this? Is it some sort of 5-HT mediated supplementary pathway that is altering the cortical processing of cranial nerve sensory inputs? That's my first guess. Thank you for your help! I'm outsourcing help so I don't end up going down another google scholar rabbit hole the day before a final...
|
[
"Not sure if this is what you are talking about, but sleep deprivation means your brain doesn't get a chance to \"flush\" itself properly.",
"When you're asleep your brain makes itself allow the brain fluid to wash over and into the whole brain, and pushes it back out to the outside of the brain. It does this many times.",
"If it doesn't get a chance to do this enough, waste products build up and cause interference with brain processes."
] |
[
"Think of it like this: When you drink alcohol or take some type of medication (cough syrup, benadryl, whatever it is), your brain is affected because the neurons can't propagate signals properly, causing you to make mistakes about what things are and such (which is why it says \"don't operate heavy machinery until you know how this medication affects you\" on almost every medicine bottle in existence). Neural fatigue happens when adenosine builds up in synapses, causing the neurons to miscommunicate, similar to how drugs and alcohol do, but to a much stronger degree, so your brain gets confused."
] |
[
"Why does this seem to have similar effects to stimulant psychosis (before lack of sleep even hits), alcohol withdrawal, or plain psychosis in general? You could also throw benedryl or other anticholinergics in there too. I’m talking visually speaking"
] |
[
"How do engineers plan for thermal expansion when laying traintracks in deserts where the daytime and nighttime temperatures are vastly different?"
] |
[
false
] | null |
[
"Railway engineer here.",
"There's some misinformation in this thread but most people have the gist of it.",
"Most modern lines will use lengths of continuously welded rail (CWR), where you can have miles of rail before there is any physical gap. This length of rail would normally be subject to large amounts of thermal expansion but because the rails are rigidly held to the sleepers, it isn't able to move. This instead builds up high thermal forces within the rail, which if weren't controlled, would eventually lead to the rail buckling in high temperatures and cracking due to contraction in cool temperatures.",
"To combat this, the rail is prestressed when laid. The amount of stress applied is designed to put the rail in a stress free zone at the average rail temperature throughout the year. In the UK, this Stress Free Temperature (SFT) is 27C.",
"Expansion joints are still used when transferring from CWR track into standard jointed track to allow for some thermal expansion at the end of the welded section.",
"In addition to carefully stressing the rail, the threat of buckling is mitigated by ensuring sufficient lateral resistance of the track - normally through maintaining the ballast shoulder (ballast being the stones that the track is normally laid within).",
"When the temperature exceeds a Critical Rail Temperature (a value roughly 30C above the SFT), there is a risk of buckling. At this point, line speeds are normally reduced as this lowers the lateral loads imparted on the track by passing trains and makes it less likely to buckle.",
"Jointed track is far less susceptible to buckling as the rail is designed to allow for thermal expansion and contraction between the joints (typically 22 yards). However, there are huge disadvantages in using jointed track for high speed, high tonnage lines which is why they are rarely used for that purpose."
] |
[
"Depending on the location and age of the railway technology, they leave small gaps in the track (really!).",
"https://en.wikipedia.org/wiki/Track_(rail_transport)#Joining_rails",
"Generally, these are being phased out but this technology has served the railways in India for over a century (in a climate where the sun would cook the rails to high temperatures during the day).",
"The disadvantage is that the gap causing the ride to be \"clickety clack\" and increased wear as train wheels literally jump between tracks thousands of times a day."
] |
[
"Engineer here",
"We use expansion joints, similar to this one: ",
"https://en.wikipedia.org/wiki/Expansion_joint#/media/File:Expansion_joint,_Hayle.jpg",
"That will allow the metal to expand and shrink depending on the temperature",
"There is expansion joints all around you guys, there are most of time unnoticed by the civilians."
] |
[
"Before the big bang?"
] |
[
false
] |
[deleted]
|
[
"The comment by Gustomucho is fairly similar to my best understanding. The article he posted was new to me and very insightful.",
"I would like to say that the idea of the \"big crunch\" is kind of dismissed, at least in its original form. The idea was that gravity would eventually bring the universe back together after the inertia of the Big Bang wore off. We now know that the universe is actually accelerating its expansion, and that the other galaxies aren't moving away from us, the space between is expanding.",
"There is another idea that I heard on a TED talk (I'll go dig for it if you want me to). The idea had to do with the law of entropy. Essentially, for a closed system, the entropy is always more likely to increase. Now, like most things in the universe, and quantum mechanics, \"likely\" doesn't mean \"always will\". So the idea is that given the universe is on an infinite time line, eventually every entropic configuration will have been expressed except one, which would be the rapid return from super high entropy to super low entropy (the conditions of the big bang). At this point, the entropy would again increase and the universe would begin expanding anew.",
"I believe this is the Big Bounce the article was talking about."
] |
[
"'We' do not really believe that the universe will have a big crunch. It all depends on the ",
"matter (Ω_M) and the dark energy density (Ω_Λ)",
" of the universe. A high mass density would lead to a big crunch, since the gravitational pull will overcome the expansion, however expanding the universe indefinitely is seems like another possibility.",
"The density, Ω = 2q0 = (2/3Λ)(c2/H2)",
"where",
"Ω = density",
"q0 = Deceleration Parameter",
"Λ = Cosmological Constant",
"c = speed of light",
"H = Hubble Constant",
"The value of the Hubble constant is estimated by measuring the redshift of distant galaxies and then determining the distances to the same galaxies (by some other method than Hubble's law). Uncertainties in the physical assumptions used to determine these distances have caused varying estimates of the Hubble constant, so the fate of the universe is still unknown, but big crunch is a possibility.",
"Regarding the first question, you might be interested in the ",
"cyclic model",
"\n."
] |
[
"Wait, here is a Wikipedia article about the ",
"Big Bounce",
". It seems to have a bit more of a complete explanation than I do, and it seems to be a little more up to date than my understanding."
] |
[
"Is it possible to identify the food someone ate through their stool?"
] |
[
false
] | null |
[
"Absolutely! In fact, that's a significant component of anthropology and paleontology. Through examining coprolites (fossilized dung), scientists can obtain information about what the poop producer (human or animal) was eating, and build a better picture of their diet and the environment and society they lived in. The ways we can get info from fossil poop range from the simple (breaking the coprolites apart to look for undigested material, microfossils of parasites, and so on) to the very complex (extracting DNA, using spectroscopic analysis to identify specific molecules associated with digestion of vegetable matter/cholesterol/etc)."
] |
[
"i expected this answer because usually i can identify what i ate just by looking at my stool. "
] |
[
"It gets even more interesting when in certain circumstances we can identify the food that someone's food ate prior to being eaten! Then we get to check out how much of the prey's internal microbiology has in common with the predators that consumed it!"
] |
[
"How does a musician tell whether a note is in tune, especially when it is being sung or played with vibrato?"
] |
[
false
] |
[deleted]
|
[
"The pitch of a note is the frequency which the instrument vibrates the air at. Our ears can naturally tell the difference between two pitches, but sometimes it takes some training to distinguish them. There are 12 standardized pitches in western music, all in half step intervals. Every other pitch is just a multiple of the other 12, or out of tune. For example, 440 hz is the A above middle C, 220 hz is the A below it, and 880 hz is the A two octaves above it. ",
"If one has perfect pitch, they just know what the 12 pitches sound like and can identify out of tune notes when they hear one that falls in between two of them. Most musicians don't have perfect pitch though, and just rely on intervals. You might need a tuner or pitch pipe or something for a reference pitch, but you'll be fine if you know all of your intervals. ",
"Anyone, even non musicians can identify intervals, even if you might not know them by name. For example, take Twinkle Twinkle Little Star. The first two notes are the same, but the jump to the next note is a perfect fifth. Sing it in your head, you should know what it sounds like. If that's exactly what you hear on a recording, then you know it's in tune. An untrained ear might not be able to tell if a note is slightly sharp or flat, but when it's wildly off you'll know. ",
"I can't explain vibrato well, but I guess I can say that our ears hone in on the \"tonal center\" of the vibrato which lets you identify if it is in tune or not. But this is very tricky, as vibrato is not always up and down, and the pitch we're looking for isn't always in the literal center. A guitar, for example, usually only uses upward vibrato, because you can't lower the pitch of a fretted note without raising it first. I believe a good vibrato usually goes sharper than it does flat, but I don't remember why and I hope someone else can answer that. "
] |
[
"Anyone, even non musicians can identify intervals, even if you might not know them by name. For example, take Twinkle Twinkle Little Star. The first two notes are the same, but the jump to the next note is a perfect fifth. Sing it in your head, you should know what it sounds like. If that's exactly what you hear on a recording, then you know it's in tune. An untrained ear might not be able to tell if a note is slightly sharp or flat, but when it's wildly off you'll know. ",
"Unfortunately, this is not true (even ignoring deaf people). People can be ",
"tone deaf",
", which means they lack the ability to discern relative pitch."
] |
[
"To add to this, why can some people tell very naturally that two sounds are in tune with each other, and other people be completely \"tone deaf\"?"
] |
[
"Why do I get freckles and does my hair go blonder when I get a lot of sun?"
] |
[
false
] | null |
[
"I'm not sure on the freckles, but I can tell you that hair getting lighter from exposure to sun is due to a phenomenon called photobleaching- essentially, the light is providing the energy necessary for pigment molecules in your hair to break down into smaller products with less conjugation that don't absorb the same wavelengths, and that their absorbances aren't as much in the visible range, leading to a whitening of the hair."
] |
[
"its your genes \nFreckles are spots usually seen on people with fair or light skin. These spots contain melanin, a pigment protein.",
"Melanin gets made when harmful ultraviolet (UV) light from the sun hits our skin. This UV light is very powerful and can damage DNA. Melanin shades and protects our DNA from the sun."
] |
[
"From what I understand, your skin is able to make \"fresh\" melanin, while the melanin in your hair is already there and can't increase due to your hair being dead except for the roots under the skin."
] |
[
"Why is IV tPA for stroke patients have to be administered (generally) in under 3 hours? Why wouldn't it be as beneficial afterwards?"
] |
[
false
] |
[deleted]
|
[
"The longer the tissue has been without blood flow, the lower the chance it will recover when flow is restored. Longer time also decreases the amount of recovery that can happen. ",
"The time frame for tPA is a risk/benefit balance. The window closes when the chance of meaningful recovery drops below the chance of significant harm due to hemorrhage."
] |
[
"This sounds like a homework question.",
"But anyway, the answer is because after several hours, all the ischemic tissue is dead, and hence restoring blood flow will do nothing but increase the risk of hemorrhage."
] |
[
"Yes, this is correct. tPA increases blood flow to ischemic regions, and can make hemorrhagic regions worse. The first step, really, is to ascertain if the stroke is ischemic or hemorrhagic. Then, if it is ischemic, and you are within time limits, you give the tPA. Neurological clinics have set up telemedicine links to ERs in most areas of the USA to be able to evaluate the \"ischemic/hemorrhagic\" question for the ER doctors to minimize the time necessary before tPA administration."
] |
[
"With a strong enough magnet, is it possible for the human body to be affected/harmed by a magnetic field?"
] |
[
false
] |
I know that there is a lot of iron in the blood, and we have quite a few different metals in our body (in tiny amounts).... what would happen to us if we were placed under the influence of an powerful magnet? Would we be harmed in any way?
|
[
"Here is a video of a frog levitating over a magnet",
"https://www.youtube.com/watch?v=A1vyB-O5i6E",
"A strong enough magnetic field would be able to get the atoms in your body to line up and become magnetic. The frog is unharmed, but I certainly wouldn't want to have any metal fillings if this were being performed on me. "
] |
[
"Magnets occur because of spinning electrons.",
"No.",
"Electrons are point-particles. They do not \"spin\". We ",
" it \"spin\" because a stationary electron with some non-zero size that is spinning would produce a magnetic field, yes. However, we are talking about quantum mechanical spin here. There is only spin up or spin down. Period. If this were the case of a spherical charge distribution spinning, you would be able to measure the magnetic field in various directions, or at least in a range between +1/2 and -1/2.",
"We know this is not the case because of this experiment:",
"http://en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experiment"
] |
[
"So what is actually going on in that video, scientifically? I can't imagine how something like this would not be painful.... I could be looking at it all wrong though."
] |
[
"Do shock waves always travel at the same speed?"
] |
[
false
] |
[deleted]
|
[
"They travel at the speed of sound",
"Uhh, no. Acoustic/sound waves travel at the speed of sound. Shock waves are not sound waves, and travel faster than sound depending on the pressure driving them. They only travel at the speed of sound in the limit of an infinitely weak shock."
] |
[
"They travel at the speed of sound",
"Uhh, no. Acoustic/sound waves travel at the speed of sound. Shock waves are not sound waves, and travel faster than sound depending on the pressure driving them. They only travel at the speed of sound in the limit of an infinitely weak shock."
] |
[
"The speed of sound of an ideal gas is a function of temperature, not of pressure. If you've got air at 1 atm at room temperature and you have air at 0.01 atm at room temperature, the speed of sound is the same in both samples. This is because ρ (density) and K (bulk modulus) are the two properties which determine the speed of sound in a fluid, and for an ideal gas, both K and ρ are linearly proportional to pressure (K = γP for an isotropic process like a sound wave and ρ = P/(R",
" T). With the additional information that the relation between speed of sound, bulk modulus, and density is c",
" = (K/ρ) you can derive the speed of sound, but I'll save you the effort and note that the speed of sound in an ideal gas is given by c = sqrt(γR",
"T)."
] |
[
"Why are fluids (and/or fluid dynamics) so hard to model?"
] |
[
false
] |
[deleted]
|
[
"The equations that describe them",
" are known, but \" theoretical understanding of the solutions to these equations is incomplete. In particular, solutions of the Navier–Stokes equations often include turbulence, which remains one of the greatest unsolved problems in physics, despite its immense importance in science and engineering.\nEven much more basic properties of the solutions to Navier–Stokes have never been proven. For the three-dimensional system of equations, and given some initial conditions, mathematicians have not yet proved that smooth solutions always exist, or that if they do exist they have bounded kinetic energy. This is called the Navier–Stokes existence and smoothness problem.\nSince understanding the Navier–Stokes equations is considered to be the first step to understanding the elusive phenomenon of turbulence, the Clay Mathematics Institute in May 2000 made this problem one of its seven Millennium Prize problems in mathematics.\""
] |
[
"Fluid mechanics isn't ",
" bad until you get to turbulence. Turbulence is a mathematical nightmare."
] |
[
"Even after making some simplifying assumptions for specific cases, what you usually wind up with are a set of coupled non-linear partial differential equations. To generate a solution for a specific set of initial conditions is impossible analytically, unless you manage to guess, because the non-linearity makes it impossible to get a truly general solution in closed form. What that leaves you with is a numerical solution, which, if you're dealing with 3 dimensions and want any kind of acceptable accuracy, is extremely computationally expensive."
] |
[
"In the history of life, was there any evolution in single celled organisms during the two billion years between the formation of prokaryotes and complex single-cell life?"
] |
[
false
] |
If so, what happened during this period?
|
[
"A big change was the evolution of photosynthesis. Cyanobacteria evolved to perform photosynthesis, which led to tons of oxygen eventually filling up the atmosphere, which lead to toxic oxygen by products being formed, which led to other bacteria evolving enzymes which could destroy those toxic oxygen by products.",
"Also, prokaryotes in general have quite a few evolutionary achievements to be proud of. The evolution of glycolysis, the chemical pathways that allow for the break down of sugar to gain energy, which is still in use amongst most organisms today. Countless other metabolic processes evolved to obtain energy from a diverse range of nutrients.",
"The flagella, a complex ion motor that contains over 40 parts and allows rapid locomotion as well as the cilia evolved. There are lots of other prokaryotic structures, but I'm not sure if they evolved before the evolution of eukaryotes or not."
] |
[
"Not sure what you're asking here. Evolution doesn't stop. It's a dynamic process."
] |
[
"I guess I wanted to know of the changes that happened during this time."
] |
[
"Can the gravity and elemental composition of the celestial bodies in our solar system have an affect on humans."
] |
[
false
] |
Was wondering if there is any scientific evidence that celestial bodies in our solar system play a part in human behaviour. Or if they can have an affect of the physiology of the body. Besides the obvious affect the sun and the orbit of the moon plays (night and day, energy). For example is the pull of the moon able to affect the water inside our bodies.
|
[
"As far as gravity is concerned, the answer is almost certainly not (at least to any appreciable degree). Consider the following:",
"The gravitational attraction between two things can be calculated using the following ",
"formula",
":",
"force = G * m_1 * m_2 / r^2\n",
"Where:",
"G is the ",
"gravitational constant",
"m_1 and m_2 are the masses of the two bodies, respectively.",
"r (for radius) is the distance between them.",
"With all that said, we can plug in numbers for two situations:",
"Gravitational force exerted by the moon on a 70kg (about 155lb) person: ",
".00232 Newtons",
"Gravitational force felt when hugging a friend: ",
".00327 Newtons",
"While there is a force exerted, it's unlikely that it does anything physiologically measurable."
] |
[
"Exactly, the doctor that helped deliver you as a baby exerted more gravity on you than Jupiter at that time."
] |
[
"Probably your hat has a stronger gravitational attraction force than any of the celest bodies, except the Moon."
] |
[
"Can I reproduce the sound on one record by exactly duplicating the grooves on a blank record?"
] |
[
false
] |
I know that records are played by placing a stylus in the grooves of a turning record. My question is, could someone take a blank record and scratch the exact same grooves into it as an Eric Clapton record, play it, and have it sound just like Eric Clapton and the rest of the band?
|
[
"Yes. That is how they make the record in the first place, from a master copy."
] |
[
"yes there are programs that can kinda play vinyl by a normal PC scanner.",
"also, laser vinyl players are toys of the audiophiles",
"http://en.publicdomainproject.org/index.php/Laser_turntable"
] |
[
"Secondary question -- Could one play a record without touching it? By perhaps magnifying the grooves and using a computer program to predict what the sound would sound like?"
] |
[
"What shape is my vision"
] |
[
false
] | null |
[
"It's circular - kinda. More precisely, the distribution of receptors in the eye is radially symmetric (save the blind spot, where the nerves connect). At the center of your field of vision, cones provide high quality, color vision. In a ring around that, rods provide fast monochromatic vision (to catch a predictor approaching from the side).",
"It's very hard to look at the edge of your vision - your eyes move, but one way is to stare forward while having someone move a blinking light into your field of view. It's amazing how far sideways you can see.",
"For diagrams and more: ",
"http://www.cis.rit.edu/people/faculty/montag/vandplite/pages/chap_9/ch9p1.html",
" or search google for \"rod distribution\""
] |
[
"Incidentally, astronomers practice that looking-without-looking trick specifically because of the better light sensitivity where you're not looking. So if you're trying to see something faint, looking near it but not at it works better."
] |
[
"We don't see a clearly-defined field like a TV screen displays - we don't really see much at all at the edge of our vision - but the field that we see through each eye is approximately circular:\n",
"http://www.ncbi.nlm.nih.gov/books/NBK220/",
"Light passes into the eye through the pupil (which is circular) and is focused on the back of the eye by the lens. Covering the back surface of the eye are cells which detect light (cones which detect different colour light, and rods which work at lower light levels but do not distinguish between colours).",
"These cells are not evenly distributed across the retina, but are heavily concentrated in a small central region, the fovea:\n",
"http://en.wikipedia.org/wiki/Fovea_centralis",
"Because of the high density of photoreceptor cells in the fovea, we can see fine detail when we focus on something. But as you can see from the graph, our visual acuity drops rapidly away from this very small region in the centre, and we only have a vague impression of objects towards the edge of our field of vision.",
"In fact, there is a gap in our field of vision due to the position in which the optic nerve connects to the eye, where there are no photoreceptors. This is the blind spot, and can easily be demonstrated:\n",
"http://faculty.washington.edu/chudler/chvision.html",
"Remarkably we do not normally notice this blind spot, even with only one eye open, because the brain fills in the missing visual information. Similarly, we do not usually notice brief moments of blindness when we blink or blurred vision when we move our eyes, nor are we constantly seeing our noses or retinal blood vessels, as vision as we perceive it does not have an immediate one-to-one relationship with the information received from the photoreceptors in the eye. Indeed, the brain can even compensate if the visual field is rotated:\n",
"http://en.wikipedia.org/wiki/Perceptual_adaptation",
"Of course, most of us have two working eyes positioned horizontally, and the brain combines information from both. This means that we can see approximately 180 degrees horizontally (of which only about 140 degrees is seen from both eyes, giving us binocular vision and therefore proper depth perception). We don't have the benefit of additional eyes to improve our vertical field of vision in the same way, so our overall field of vision is wider than it is high - but rather than being a neat rectangle like a TV screen, it's more like two partially overlapping circles. Again, the brain ensures that we perceive a consistent and contiguous image when those two fields are merged. ",
"So, biologically, given the shape of the pupil and the retina, the field of vision we have in a particular eye is roughly circular, being very sharp in the centre but vague and blurred towards the edges, and it has a hole in it. Because we have two eyes positioned horizontally from each other, our overall field of vision is wider than it is high. But what we perceive as vision is heavily processed by the brain, which combines this information and attempts to compensate for limitations of our biology."
] |
[
"What is the science behind the possibility of immortality? Would 'nanorobots' be necessary or could we potentially live forever by reprogramming cell death and repair in our bodies?"
] |
[
false
] |
[deleted]
|
[
"Well right off the top of my head, I'd say until we figure out how to stop cancer, immortality ain't happening. From what I understand (the bio guys correct me if I'm wrong), like any system, as your cells replicate, there's a very small chance that your DNA gets copied over incorrectly. Over time, these errors build up eventually causing the cell to stop functioning or replicate uncontrollably. So even though it might be possible to live forever without getting AIDS, its just a matter of time before we all get cancer.",
"TL;DR curing cancer is a prerequisite to living forever"
] |
[
"I think a major issue would be DNA replication. ",
"Telomeres",
" aren't regenerated when DNA is reproduced, I am probably going to butcher the description but when DNA is replicated the DNA polymerase can't start a strand from scratch so it starts just before the end (at least in one direction, I'm not even gonna attempt to explain okazaki fragments) . The end is made of repeated strings of basically junk DNA to give it extra room to work with, but this results in a limited number of replications. ",
"The Hayflick Limit",
" is the point at which cells can no longer effectively replicate the DNA. Research is being done on activating telomerase to lengthen telomeres but I don't know how far along it is. Hope I didn't butcher that too much."
] |
[
"Which is why the nanobots would be programmed to detect cancerous cells and destroy them! Just poke a hole in the membrane and let it deflate like a water balloon."
] |
[
"What is worse on our skin, a strong acid or a strong base?"
] |
[
false
] | null |
[
"\"Acids eat you from the inside out, bases eat you from the outside in\". I'd be more concerned about bases, high molarity sodium hydroxide will turn you (quite literally) into soap via saponification if you get it on you."
] |
[
"This happened to me in my analytical chemistry lab way back when I was learning proper handling. I got a drop of NaOH on my finger and immediately washed it off with water, only to find my finger tip felt \"greasy\". It was the fat of my skin being turned into soap! It was just a little bit, no lasting damage, but enough to freak me out. I also had no fingerprint on that finger for a short time. Learned a lesson that day: don't rush things when handling chemicals!"
] |
[
"Did it hurt...?"
] |
[
"Doctors: what is your thought process when choosing an antibiotic for patient?"
] |
[
false
] |
[deleted]
|
[
"Antibiotic choice is predicated on a number of factors. There are a number of major classes of antibiotics (penicillin derived antibiotics are only one such class), each of which works in a different mechanism that lends itself towards different biologic activity. Efficacy is certainly the first thing you look at - whether you have culture data showing microbe sensitivities to specific antibiotics, or just are treating empirically (eg if you suspect gram negative bacteria, you may choose an antibiotic from the aminoglycoside class). The next thing you would look at is the side effect profile. When many drugs can achieve the same primary goal of killing bacteria, you want to select one that damages the patient as little as possible. This includes things like avoiding certain classes of medicines in young children/pregnant women (tetracyclines and fluoroquinolones), not using a medicine the patient is allergic towards, watching out for possible medication interactions, etc. Recently, there has been a push towards the principle of antibiotic stewardship, where we try to use as narrow an antibiotic as possible to prevent further development of antibiotic resistance. This means that if two antibiotics are equally effective and safe, we choose the one that is most specific towards killing the bacteria currently infecting the patient, rather than using broad-spectrum coverage. With that said, the clinical picture is also important and if the patient is critically ill early coverage with broad-spectrum antibiotics are warranted. And lastly, if there are a number of antibiotics that fulfill the above criteria, you go with whatever is in your hospital formulary/cheap/available in the right route of administration (eg only IV vs only oral etc).",
"What this all boils down to is basically a fairly standard set of protocols for most infections. Many groups, such as the ",
"IDSA",
", publish consensus guidelines for which antibiotics are indicated for which infections. The typical strategy is to treat empirically until you get culture and sensitivity results, and then narrow according to individual patient requirements."
] |
[
"Experimental Pharmacologist, infectious disease.",
"If taught med students on this. Its fairly standard in theory but in practice some tend to ignore the guidelines. The theory is, you use as much information as you can to predict; Sepsis with skin infection - mostly likely gram + 50-60% chance of S. aureus, 5-10% Strep. So if unknown use broad spectrum for both Vanco + 3rd gen cephalosporin to cover the chance of gram negative. If you have a gram stain / culture and it turns out to be strep switch to pen G. Its simple in theory; pick the one with the highest percent of positive outcomes, narrowest spectrum, and low resistance (including protein synthesis inhibitors for toxic shock).\nIn practice, what I see doctors often do is pick the one that covers the most bases. Sure, picking the narrow spectrum, on a society level, will be the most beneficial but on my individual patient level I see many wanting to use daptomycin over pen G to cover all their bases. Good in the short term, bad in the long run."
] |
[
"Recent Pharmacy Grad-",
"This is how we're taught in school, and yes in practice its like pulling teeth sometimes to get physicians to buy into that idea. In just my last year of school, I had to talk 3 doctors out of using Tigecycline first line in patients. For those that don't know tigecycline, its a very important antibiotic in that its new, its very broad-spectrum, and resistance is still low with it. The general consensus with it is to 'save' this antibiotic as someday all to soon the traditional antibiotics we have now will be ineffective."
] |
[
"Is it feasible for a digital cameras to use cheaper lenses with less glass and have the distortion removed via software after it is extracted from the sensor?"
] |
[
false
] |
Camera lenses can be very expensive, they can contain many pieces of glass to remove distortion and all that extra glass can increase the cost significantly. I was wondering if it was possible for a lens to contain fewer pieces of glass, and therefore be cheaper, and instead of correcting the distortion with extra glass before the light hits the sensor it would have a chip embedded in it to tell the camera what type of distortion it has so the camera can remove the distortion with software after it is extracted from the sensor? Is something like that possible?
|
[
"It's generally possible to correct all manner of imaging defects (geometric distortion, lens blur, motion blur, noise, etc.) to varying degrees, but in all cases it' s a lossy process.",
"If your only distortion is geometric, and you otherwise have a sharp lens and a great sensor, then you can certainly invert the geometric distortion and have a reasonable looking image. But you will lose effective resolution in places."
] |
[
"Nothing beats a good piece of glass"
] |
[
"Geometric distortion (and to a small extent) chromatic aberration can be corrected digitally, with some loss of detail due to interpolation. But spherical aberration, coma, diffraction, and flare all reduce the amount of information reaching the sensor. Perhaps lenses are being designed for special purposes that produce sharper images by allowing more distortion and chromatic aberation, but they aren't widely available.",
"Note that chromatic aberration can only be partly corrected. A full frame DSLR with a wide angle lens will often show the edges of the individual color channels misaligned from each other by a pixel or two, and DxO software does a good job correcting it, with a noticeable increase in image quality. But the light reaching the sensor is a full spectrum, while the sensor records only three colors. If the red channel was misaligned by two pixels compared to the blue channel, the light recorded by the red channel was also \"smeared\" by chromatic aberration between deep red and bluish-red, but that information isn't recorded."
] |
[
"Most soaps advertise as being able to get rid of 99.9% of germs. Do our bodies do the same when dealing with viruses/bacteria, or do we eliminate them completely?"
] |
[
false
] | null |
[
"Soaps work by breaking down proteins that form the outer shell of “germs”. ",
"I don’t think I see soaps often claim to kill 99%, but disinfectants and sanitizers do claim this. These work in a similar manner, and often these claims require contact with the surface being disinfected to remain in contact with the solution for a prolong time period, like 10-30 seconds to reach full 99%. ",
"The body is very strange and a great deal of things we think of as being “germs” and “viruses” are actually found on and inside of us very routinely at all times. It seems there is a strange balance in our bodies between all of these other “germs” and “viruses” and we are only starting to discover that this balance is possibly more important than killing all the “bad” “germs and viruses”.",
"Our bodies do not always fully eliminate “germs and viruses”, the body simply removes enough of them that it no longer causes us any harm. There are many cases of viruses that are able to hide from the bodies cleaning system and return as reinfections or reactivate later in our lives. Chicken pox and shingles being a great example."
] |
[
"Doesn't detract from your point, but a quick correction: most soaps are bactericidal by virtue of their surfactant and detergent properties. They don't break down proteins; they disrupt the cell membrane/wall."
] |
[
"Thank you for this. I was sitting here aggravated but didn’t really know if I felt like getting into this discussion."
] |
[
"How close could a rogue planet feasibly get to us or our solar system without being detected?"
] |
[
false
] | null |
[
"Why are people answering with \"that can't happen?\"",
"A planet-sized mass that was ejected from a solar system or formed outside of one could be orbiting the galaxy and its orbit around the galaxy could eventually intersect with our solar system's orbit around the galaxy.",
"Our solar system orbits the milky way at 230000 m/s so even if the planetary sized object was coming straight at us in the other direction its relative speed towards us would be 460000 m/s, so it would take ~3.8 days to travel the distance between the earth and the sun. That would be more than enough time for an amateur astronomer to notice it if it got around 1 A.U. away from us (distance between the earth and sun). If it was orbiting the galaxy in the same direction we do it would take even longer to traverse that relative distance towards us because its relative speed would be much lower. It's an entirely different question as to whether they'd notice that it was a previously undocumented object though.",
"I don't know what % of the sky professional telescopes are monitoring at any given time, so seeing it before it got within the solar system would be some amount of luck given where the experimental telescopes are pointed when it comes by."
] |
[
"\"No chance of a rogue planet because planets orbit stars\" If that's what you believe I don't want to listen to your podcast, Planets are knocked out of their star's gravitational influence all the time. "
] |
[
"\"No chance of a rogue planet because planets orbit stars\" If that's what you believe I don't want to listen to your podcast, Planets are knocked out of their star's gravitational influence all the time. "
] |
[
"Sequenced rice genome shows rice cells have more genes (50,000) than humans (26,000). Does this mean rice are more evolved than humans?"
] |
[
false
] |
1) Does this mean that the rice genome is more complex? 2) Do we have to abandon the idea that the more genes an organism has, the more evolved it is?
|
[
"No. # of gene does not represent how far you've evolved.",
"Also what you mean by \"more evolved\"? Some bacteria can undergo a generation every 20 minutes, does that make them more evolved than everything else on Earth?",
"The reason they have more genes is because they're plants.....which in general have more genes than mammals because they can't just up and walk away from whatever's bothering them.",
"Therefore they have to develop >chemical/biological responses< to things that affect them which means they generally need more genes to store the information for said chemical/biological responses.",
"Animal is cold/hot? Walks into the shade/sun. Problem solved.\nPlant is cold/hot?.....Have to start synthesizing proteins or chemicals such to insulate/cool itself. ",
"Animal is being eaten by insects? Roll around in the dirt & runs away.\nPlants? .......%@!# time to make chemical weapons against those pesky pests."
] |
[
"So in essence, plants are genetically more complex because they are biologically more complex forms of life?"
] |
[
"\"more evolved\" is subjective. ",
"Yes, rice dna is more ",
" than human dna. An onion is actually 12 times more complex than a human dna, but as you can probably guess, we are more complex creatures than an onion. The reason is that a large portion of an onion, or rice's dna structure, is effectively, ",
"junk",
". "
] |
[
"Why does more drag on the fins on a rocket provide more stability?"
] |
[
false
] |
I was reading this article and the topic came up. Why does more drag on the fins mean more stability for the rocket?
|
[
"Simple answer: because drag slows the fins, keeping them directly behind the head of the rocket. Any time it starts to veer off course, the fins move back behind the head again and straighten it's trajectory back up. It's the exact same concept as fletchings on arrows that have been used for tens of thousands of years."
] |
[
"Drag is a force parallel with the flow so no I'm not. And fins are airfoils. Flat plates, arc, and diamond cross sections are all used depending on how simple the rocket is and what Mach regime the rocket flys in and are all considered airfoils. A simple way to think about it would be to look at the drag and lift vectors and their horizontal and vertical displacement from the CG. For a long tube lift has a much larger moment arm than drag. I'm not saying drag doesn't help, but lift is the main driver."
] |
[
"Fin drag is only a minor component to the stability. It's the fin lift that does the work. As long as your Center of Gravity is in front of your Center of Pressure you will be stable. If the rocket gets to a positive angle of attack the fins will generate lift, a force perpendicular to the airflow. So for a positive angle of attack the fins will generate force pointed up. Which when resolved around the Center of Gravity will result in a moment that will move the nose back down."
] |
[
"Why isn't a Bose-Einstein condensate get talked about much in lower level science classes even though it's considered a \"state of matter\"Or is this different than being a solid, liquid, gas, or plasma?"
] |
[
false
] | null |
[
"Just to name a few, some other phase transitions are:",
"superconductivity",
"superfluidity",
"the ",
"ferromagnetic/paramagnetic",
" transition."
] |
[
"Just to name a few, some other phase transitions are:",
"superconductivity",
"superfluidity",
"the ",
"ferromagnetic/paramagnetic",
" transition."
] |
[
"This all may be off topic for this sub (its rarely the scientists directly making decisions about what topics are taught or not taught in schools, after all).",
"On the assumption that it's okay for a science teacher to respond to this question: Much of what I do involves helping children understand the world around them - and the idea that there are laws and patterns that underlie all of it that can be discerned through observation and experimentation.",
"It's simply not possible with science classroom technology to give students ",
" with unusual states of matter. When I've done units on matter, I'll mention that there are other states beyond the four typically taught - and usually I'll mention the Bose-Einstein Condensate by name and try to answer a question or two about it. But I won't linger on it, because it's in the realm of things for which students would simply have to ",
" - and that's not encouraging scientific thinking in them."
] |
[
"Has nuclear weapons testing had any appreciable effect on the planet’s background radiation and/or surface temperature?"
] |
[
false
] |
In the 20th century, over 2000 nuclear bombs were detonated in unpopulated areas. We know that the bombs in Nagasaki and Fukushima left many people who were not in the immediate fallout to suffer (and often die) from radiation sickness and terrible burns. As the test sites were far away from human habitats (namely the Pacific Ocean and depopulated Kazakhstan) my question is regarding how the blasts would have dissipated across the planet and its atmosphere. Did they contribute to global warming (knowing that the blasts release immense amounts of heat) or is the effect negligible compared to the proliferation of fossil fuel use.
|
[
"As the test sites were far away from human habitats (namely the Pacific Ocean and depopulated Kazakhstan)",
"Or Nevada. Not that far away from people.",
"https://www.atomicheritage.org/history/nevada-test-site-downwinders",
"The effect on the temperature is negligible. More general: Direct heat release doesn't have a long-lasting effect. The atmosphere is close to an equilibrium between incoming radiation and outgoing radiation, and the position of this equilibrium doesn't depend on its current temperature. But even in terms of direct heat the input from nuclear weapons is negligible: A 10 MT explosion (that is a huge test) releases an energy of 4*10",
" J, the global human energy consumption of a few minutes.",
"Nuclear weapons did have a relevant effect on some specific parts of the background radiation: We made carbon dating useless for material more recent than the weapon tests - they produced too much C-14 that decays over time now. They also produced a few isotopes that don't occur naturally. In terms of total radiation dose the impact is small (with some local exceptions: see above)."
] |
[
"over 2000 nuclear bombs were detonated in unpopulated areas",
"Only about 200 were detonated in the atmosphere. The rest were underground.",
"We know that the bombs in Nagasaki and Fukushima ",
"I assume you mean Hiroshima...",
"blasts would have dissipated across the planet and its atmosphere",
"Fallout from atmospheric tests did move through the atmosphere at long distances. Not the blast effects. There were health effects from the radiation for populations downwind of them, and populations living in the northern hemisphere (which is where most of the atmospheric testing took place). But that doesn't seem to be what you're really asking about.",
"Did they contribute to global warming (knowing that the blasts release immense amounts of heat) or is the effect negligible compared to the proliferation of fossil fuel use.",
"The amount of heat from a nuclear weapon is intense on a local scale but small on a global scale. To put it into perspective, the Sun globally deposits the equivalent of 117 thousand Hiroshima-sized bombs per minute onto the Earth. ",
"The issue with global warming/climate change isn't the energy that is ",
" to the atmosphere, it's whether the energy is ",
". Carbon dioxide acts like a one-way window in which the energy of the Sun can come in but not go out again. This is an important distinction: no amount of burning of fossil fuels is going to raise the temperature ",
". But it will make it so that the Sun's energy gets trapped more easily, which will raise the temperature on average globally. (It should also be noted that climate change is more complicated than just warming — in many places it will translate to extreme cold as well.)"
] |
[
"In terms of total radiation dose the impact is small (with some local exceptions: see above).",
"In terms of health effects, it depends on what model of low-dose harm you use. In the northern hemisphere the amount of radiation that non-downwinders picked up from the testing was not negligible, and the populations were very large, so if there is a small effect then that translates to quite a lot of cancers over the course of the Cold War (on the order of tens or hundreds of thousands — small considering the total number of cancers in those populations over that period, but a large \"raw\" number)."
] |
[
"How can smoking cause cancer years after the smoker has quit?"
] |
[
false
] |
[deleted]
|
[
"Ok is your question why smoking causes cancer after years of cessation or are you asking why the risk of cancer from smoking decreases drastically after cessation? ",
"For the first question, cigarettes contain hundreds upon hundreds of carcinogens (stuff that damage your cells) that wreaks havoc in your lungs, mouth, etc (anywhere the smoke hits). It also increases your risk for cancer in other parts of your body such as the bladder, as those carcinogens travel in your blood to those organs. ",
"In a non smoker, cells in the body make lots of “mistakes” over the course of a persons lifetime naturally. One of the reasons why we age. However, when you smoke on top of that, you are introducing many more “mistakes” a cell can make when it is reproducing itself. ",
"These “mistakes” accumulate and remain with the smoker even if they stop smoking. One day, long after a person might have stopped smoking, a natural mistake can occur in one of those cells that push it over the threshold line causing cancer. ",
"FYI \nThese “mistakes” I’m talking about are genetic mutations that occur in the cells, usually stem cells. With enough accumulation of these genetic mutations, a cell might not be able to function normally or worse not recognize that it is functioning abnormally. ",
"Hope this helps."
] |
[
"Tumors have three stages :",
"Initiation : the cell came in contact with a carcinogenic substance or radiations. The DNA has been altered. At this stage, the cell can either survive or commit apoptosis (programmed death aka suicide). If it survives, the DNA has either been repaired or not. The cell is now initiated, if there has been no repair.",
"Promotion : The initiated cell divided and some genes regulating proliferation mutated. The cell now starts to divide quicker than usual. A certain mass of mutated cells starts to form. The mass is still reversible, which means we can get back to normal cells, but can lie dormant until the right conditions make it progress.",
"Progression : The mass gains autonomy, it can proliferate on it's own, it becomes an important tumor, mutations occur between the mutated cells (a perfect example of evolution), so they can escape the immune system.",
"What happens with someone who quits smoking is that they might have initiated or promoted cells. With time, those dormant cells acquired the right conditions to progress towards a tumor, even though the person stopped smoking years ago.",
"That's why some people who worked in asbestos mines developed lung cancer years after they stopped working there, for example.",
"I might have some things wrong in my explanation, someone with better knowledge of carcinogenesis could give a better answer."
] |
[
"Right now, not really, though I'd try to avoid anything known to be acutely (not developmentally) toxic particularly to immune function, like sources of other smoke in general (not just cigarettes, wood smoke still has toxicants in it), mothballs (napthalene) and many pesticides to give you examples (ie. limit exposure to other types of toxicants). The immune system typically shuts down most cancer cells before they become a problem, so cancer can reflect a failure of the immune system, or the success of the cancer to evade the immune system. As for your twin example, I think its highly likely that the healthier twin would be less likely to cancer, but it depends on the details and if you're genetically predisposed to getting lung cancer, then a healthier lifestyle may not help you all that much.",
"The other thing I'd recommend is a pratical consideration of getting screened for cancer regularly. Most cancers are curable if they are discovered at an early stage, so if you think you're at risk on the basis of your exposure burden or genetics, then getting screened yearly or even more frequently is your best chance of surviving it if you do get it."
] |
[
"What Affects The Rate At Which Objects Fall?"
] |
[
false
] | null |
[
"Yes, it's air resistance."
] |
[
"Yes, it's air resistance."
] |
[
"Yes, it's air resistance."
] |
[
"If I demand too much of a certain brain area, like the visual cortex, and get a headache, will it feel first in that exact head area?"
] |
[
false
] | null |
[
"You can't feel pain in your brain. Headaches aren't inside the brain, they are in the surrounding tissue."
] |
[
"you don't get headaches because of using your brain. headaches usually correspond to inflammation (or abnormal activation) of the trigeminal nerve that innervates your face.",
"if anything, you might sometimes get eyestrain headaches from overwork, which correspond to fatigue in eye muscles and tissues."
] |
[
"I know that. But I was wondering if the surrounding tissue has some correlation with each part of the brain."
] |
[
"Zeno's Paradox. Does this work?"
] |
[
false
] | null |
[
"This is not a valid, physical solution. If we look at things classically (pre-quantum mechanics), then a basic assumption is that things move continuously and a most, if not all, of tools that we use would have to be completely redone to use a discrete movement framework. But these tools have given too many correct predictions that we can't throw them out for something that is, essentially, untestable in the classical realm. Especially since the paradox has a valid accepted solution (below). If we look at things modernly, post-quantum mechanics, then the notion of precise location means nothing and the entire paradox would have to be completely reformulated because it simply does not apply due to the nature of quantum mechanics. There is a very real ",
"Quantum Zeno Effect",
", though I don't know how much it relates to the original problem.",
"To resolve Zeno's Paradox (classically), let's look at the time that it takes to do each half-step. Let's say that we are travelling at 10m/s (meters per second) and we want to go 100 meters. The time in between first few half-steps are:",
"And so the total time that it takes to do the first 5 halves is the sum of all these: 9.6875 seconds. Can we, then, find a general formula for the time it takes to do the first \"n\" steps? Well, the distance that we have to travel between the n-1 half and the nth step is going to be 100/2",
" which means that the formula for t_n is this divided by the speed:",
"plug in the first few n and you'll see that it matches our calculations. So the time it takes to go the first n-steps is:",
"This is what we call a Finite Geometric Series and it has the formula:",
"If we plug in n=5, we have T_5=10(1-1/32)=310/32 = 9.6875 as we had before.",
"Okay, so that's fine, we figured out how long it takes to do a finite number of steps. Great! But we're actually concerned with how long it takes to do all the infinite number of halves it takes to get to the end. To calculate this, let's see what happens to 1/2",
" as n gets very very large. Well, when we divide by larger and larger numbers, we end up with smaller and smaller numbers. In particular, we see that as n gets infinitely large, then 1/2",
" gets infinitely small! So what we say is that as n goes off to infinity, the value of 1/2",
" goes to 0. This is the basic idea of ",
"Limits",
" from calculus.",
"What this then says is that as n goes off to infinity, the value of T_n=10(1-1/2",
") will have smaller and smaller contributions from the 1/2",
" until it eventually does nothing! We can then say that T_infty = 10, as we would have expected. For more information, look at the ",
"Geometric Series",
" page of wikipedia.",
"So, in conclusion, even though it takes an infinite number of steps to move from point a to point b, the time it takes to do each step gets smaller and smaller and the principles of limits say that we can add up all these positive and decreasing time values to end up with a finite number. Infinite Steps does ",
" imply Infinite Time."
] |
[
"I understand limits. I don't think it's weird that the infinite sum of constantly decreasing numbers tends to a number and doesn't go over it.",
"This is the problem I have. Ok, so we wanna move 10 meters and let's say that takes 2 seconds. Then moving 1 meter would take 0.2 seconds. The problem is that there are infinite (aleph1) numbers between 0 and 10 and we have to pass every one of those numbers. ",
"How long does it take to get to 1 meter? 0.2 seconds. Well, how long does it take to get to each of the infinite numbers between 0 and 1? If getting to any number between 0 and 1 takes any time at all, and there are an infinite amount of numbers between 0 and 1, then it should take infinite time to get to 1. Infact, since there are infinite numbers between any number it would take infinite time to to move any distance.",
"On the other hand, if moving past the infinite numbers takes no time, then getting from 0 to 1 would take no time, so we could teleport, which we can't.",
"Observation tells me that i can move 10 meters in 2 seconds fairly essily. B reasoning says It should either take 0 time or infinite time."
] |
[
"If infinite sums say that an infinite number of positive values can add up to a single, finite value, then Integrals say that an aleph 1 amount of zeroes can add up to a single finite, positive value.",
"Yes, to move from point A to point B, we need to hit every value inbetween and there are an uncountable number of things to hit. We can do a similar thing as we did above by using the finite to go to the infinite:",
"Let's say that we are trying to go from 0 to 100 again, at 10m/s. But let's break it down into a finite number of steps. Let's break it up into steps of size d. So the time it takes to traverse each step is d/10. And so the total time it takes to go 100 meters is the time it takes to go from 0 to d, d to 2d, 2d to 3d all the way until we get to 100. If 100/d is N with remainder R, (so 100=Nd+R and R<d) then the time it takes to go 100 meters is going to be inbetween Nd/10 and (N+1)d/10. This means the time is somewhere in between",
"This is valid for no matter how small we make the steps. So what happens if we take d to be zero? Well, this means that the time it takes to go each step is zero, but the total time it takes is in between ",
"or is just 10. Again, as expected. Intuitively, this means that a uncountably many zeroes add up to a finite number. So even though we have to go to every single number, the time it takes to go \"in between\" numbers (whatever that means) is zero, so it doesn't matter that we have to hit an uncountable number of places because the time inbetween them is short enough (zero) for them to add up to a finite, positive value. This is the basic idea of Riemann Integrals.",
"This is the standard treatment of things, which builds up infinitesimally small thing by going down from finite things. There is ",
"Non-Standard Analysis",
" which goes in the other way, it axiomizes infinitesimal numbers (things that are different but have zero distance between them) and builds up integrals and derivatives by essentially adding an uncountable number of these zero distances to get a positive value."
] |
[
"How does soap clean?"
] |
[
false
] |
title says it all, how does using a bar of soap clean you, on a scientific level?
|
[
"Soap molecules form micelles around dirt/contaminants/bacteria. A micelle is effectively a ball of soap molecules that surround the dirt and hold it in suspension in the water.",
"The soap molecules have a hydrophobic tail and a hydrophillic head. The heads of the molecules all face outward towards the water, and the tails all face towards each other. The dirt/contaminants get trapped between the tails. "
] |
[
"Most molecules can be described as being \"polar\" (which simply speaking means they dissolve in water), or \"nonpoloar\" (which are greasy substances that don't dissolve in water). Washing with water can easily clean the \"polar\" dirt away, but not the \"nonpolar\".",
"Soaps work because they're both polar and nonpolar. They have a long greasy tail, and a short polar head. Their tail can dissolve the greasy dirt, and their head can dissolve in water. They act as a link between the water and the grease, and allow the grease to wash away with the water.",
"The membranes of cells are composed of similar molecules (called phospholipids). Soap can dissolve these membranes, causing the cells to burst open, killing bacteria. Don't worry, your skin is protected (but don't go injecting soap into your bloodstream)."
] |
[
"Soap consists of molecules which have two kinds of ends, one end which \"likes\" water and similar molecules (hydrophilic), and one end which \"likes\" oil and similar molecules (hydrophobic). One of the challenges to removing dirt and some organisms from your skin is that they are oily and repel water, so they are more prone to stick to your skin than be washed off. One end of molecules in the soap is able to interact with these molecules more effectively than water is. Molecules in the soap surround these normally water-hating substances. But, because the soap molecules also have a \"water loving\" end, they can be readily washed away by water, along with the gunk that was on your hands."
] |
[
"How come skydivers, astronauts and pilots don't suffer from an equivalent of \"the bends\" when they are hurtling towards the ground?"
] |
[
false
] |
[deleted]
|
[
"Keep in mind the relative differences in pressure - even if you go into space, you only decrease by 1 atmosphere. But the overpressure at even 100 feet deep (which is well within the reach of a scuba diver) is ",
"over 9 atm",
" ",
"over 3 atm",
". ",
"Edit: Fixed to underwater, not underground."
] |
[
"Astronauts (and presumably Felix Baumgartner) do have to worry about the bends, although not when hurtling towards the ground (the bends, if I understand correctly, only occur due to a rapid decrease in pressure. I'm not aware of any equivalent problem for a rapid increase in pressure). Before spacewalks, astronauts used to breath pure oxygen through a mask for several hours (see ",
"this",
", for example). This would purge their blood of nitrogen and allow them to perform the spacewalk in suits that are generally around 4-5 PSI pure oxygen (as opposed to the ~14.7 PSI oxygen/nitrogen environment that the ISS/Shuttle operate at).",
"The oxygen pre-breathing procedure was changed in favor of a campout in the airlock, in a reduced pressure environment. The EVA astronauts would spend the night before the EVA in the airlock at a reduced (10.2 PSI) ambient pressure; this would effectively purge their blood of dissolved nitrogen as they slept. This is the current procedure used on the ISS for EVAs. For some info about the campout procedures, see ",
"this PDF",
" (n.b., I only skimmed the document. I'm not sure of how much it really says about the procedure).",
"As for skydivers, someone else will have to answer. I'd ",
" that it's similar to high(ish) altitude mountaineers, in that the pressure never really gets so low that dissolved nitrogen becomes a problem. Remember, there are Himalayan tribes that live at well above 15,000 feet, and most skydivers don't really get even that high. But that's a layman's guess."
] |
[
"The pressure of water vs. the pressure of air are different."
] |
[
"Does birth order have an impact on someone's personality?"
] |
[
false
] | null |
[
"the answer is either \"no\" or \"not really\". many studies of this exist, it's an old and popular question. here's one:",
"https://journals.sagepub.com/doi/pdf/10.1002/per.2285",
"there they find no effect of birth order on the Big Five personality dimensions (extraversion, conscientiousness, neuroticism, openness, agreeableness) or other factors (intelligence, risk aversion).",
"here's another study showing no difference in personality traits, but confirming a previously-reported ",
" decline [",
" this meaning 'small negative correlation'] in intelligence with birth order\n",
"https://www.pnas.org/content/pnas/112/46/14224.full.pdf",
"Both of those studies were based on samples of thousands of people. Both are relatively recent (previous decade). You can find many more along those lines, generally in agreement:",
"https://scholar.google.com/scholar?hl=en&as_sdt=0%2C50&q=big+five+personality%2C+birth+order&btnG=",
"If you look back further, there were ",
" studies showing effects of birth order on Big Five dimensions, e.g. this was one of the latest:\n",
"https://journals.sagepub.com/doi/pdf/10.1111/1467-9280.00193",
"but that study is based in third-person data, i.e. having individuals rate their ",
" on personality traits.",
"So, some confirmation that people ",
" in birth-order effects on personality, in consistent ways - but little evidence that such effects are actually real. from an observer's viewpoint, 'personality' might get confounded with sibling dynamics, where elder and younger siblings do indeed behave differently. but those differences may not be attributable to personality per se, rather, to place in the sibling hierarchy (favoritism, struggle for access to resources, etc etc etc).",
"I found this as well, ",
"a commentary by Sulloway from 1995",
", detailing why many evolutionary theorists have postulated that there ",
" be effects of birth order on personality; but also critiquing how such theoretical approaches might have affected how data are published...",
"Also on that GoogleScholar search page, you can find this review by Sulloway from 1999:\n",
"http://www.sulloway.org/BirthOrder-Sulloway-1999a.pdf",
"There he lists what he thinks are good estimates of correlations between birth order and personality characteristics - all significant! but ",
". and, remember, if you have a large enough sample size, you can find significant correlation between just about any two variables that exist in the same world. but is it meaningful? (oh plus, it seems that this data, as well, is based on intersubjective ratings, i.e. siblings rating themselves and their siblings)..."
] |
[
"https://time.com/5953372/birth-order-personality-traits/",
"I had a college sociology professor who stated order did determine certain personality traits. He gave the specific example that first-born children were more likely to fly a plane with a team, while a youngest child would be more likely to become a solo fighter pilot. Something about the idea the first-born never really feels totally sure of themselves due to extra coddling in childhood, while subsequent children have less and less coddling. I suppose the parent is more knowledgeable and more tired. It's an interesting idea, but I do think that with all things there are anomalies, like what if the first two children are boys, but the youngest is a girl. Would the parents treat them differently because they may be the baby, but the first girl? It's a lot to think about. \nLong story short, I'd say \"yes.\""
] |
[
"Your formative experiences are shaped by the people in your immediate household. No one can deny that.",
"Those experiences are going to be wildly different depending on the number of people raising you, ",
" personalities, and their dynamic.",
"The factors that shape our personalities are so varied and so situational, as are our relationships with family --so I don't think there's any reasonable way to study it comparatively and draw hard and fast rules."
] |
[
"When I hear a sonic boom, am I hearing all the sound generated by the speeding projectile over a certain distance all in one go?"
] |
[
false
] |
This is how I interpret this diagram of a mach cone if we place ourselves at the red dot, but I haven't yet (after some brief internet searching) found anywhere that explains it this way.
|
[
"No. This is a common misunderstanding about what the source of the noise you hear as the result of the passage of a shock wave is.",
"Those circles don't represent noise as you think of it - stuff like birdsong of even the roar of the plane's engines. Instead, they represent the disturbance of the air generated by the <thing> as it moves. Even things that are inherently silent - like a bullet - generate shock waves, and therefore sonic booms. ",
"As something moves through air (or water, or jello, etc.) it generates a pressure wave - it has to provide force to move the air. That pressure wave moves at the speed of sound away from the object. If the object is moving slower than the speed of sound, the air \"gets the news\" that it's coming from the presence of this pressure wave - in principle, if the object moves at a small fraction of the speed of sound, even the air tens or hundreds of feet away can respond to the movement of the object. As the object gets closer and closer to the speed of sound, the \"advance notice\" that the air gets comes closer and closer in time to the actual physical passage of the object - the air doesn't start moving 1 second in advance of the object, it starts moving half a second in advance, or a quarter of a second, etc. At the speed of sound, we have a problem: even the air that is just about to be shoved out of the way has no idea there's an object coming. It can't adjust its position beforehand. When it gets hit, it has to move ",
" quickly (because the object is moving very quickly), and this requires a ",
" of force -- that is, a strong pressure wave is generated. This is the ",
" - it's actually very nearly a physical discontinuity. In the space of only a few hundred nanometers (about the size of the smallest bacteria), the pressure and temperature of the air increase dramatically. The entire time an object is moving supersonically it's dragging a shock like this around.",
"The shock wave is what you perceive as a \"sonic boom\" - it's essentially an impulse change in pressure (i.e. the pressure changes almost instantaneously), which your brain interprets as broad-spectrum noise - the same type of noise a balloon makes when it pops, only generally much louder. But as I said, this shock wave doesn't rely on the object making noise - again, a bullet makes no noise that isn't due to its interaction with the air. It's simply a consequence of the passage of the object. ",
"e: Maybe this is a shorter way to explain it:",
"No, you're definitely not hearing all the sound the object has made because ",
" - it's moving so fast that it reaches you ",
" any sound it makes! Only after it passes can you begin to hear any sound that it made."
] |
[
"This is really a great explanation, thank you. I can see now why I kept seeing bow-wave comparisons in articles.",
"I just have one question: what is a physical discontinuity?"
] |
[
"A discontinuity is when the value of some property changes instantly. In reality, there don't appear to be any real discontinuities, but some things can change so quickly or across such short distances that they are very, very close to the concept of a mathematical discontinuity, and we use that as an approximation in physics all the time so we don't have to worry about the details of how a system is changing if it happens very quickly.",
"This",
" is an example of what a discontinuity is. This \"step function\" has a value of -1 for values of x <= to 0, but then suddenly is equal to +1 for x > 0, without ever transitioning between the two."
] |
[
"Why is exercise painful?"
] |
[
false
] |
Exercise is supposed to be healthy; so why is it painful? Surely if it increased our chances of survival, wouldn't it make more sense for exercise to be pleasurable, thus encouraging us to do it more often? Are there any benefits at all to having it this way?
|
[
"Exercise involves slightly breaking down muscle tissue by forming micro-tears. Then the body rebuilds the muscles, over shooting a bit so that it can deal with the increased load. Repeat many cycles of that and the muscles become stronger."
] |
[
"For some people it is pleasurable... You produce endorphins when you exercise which give you a feeling of well being... When I am stressed out I go lift weight or run and it defiantly improves my mood.",
"You are probably out of shape and trying to push yourself too much thus having cramping and pain."
] |
[
"Due to the excess demand for energy in exercise, pyruvate is reduced to lactic acid in anaerobic respiration in muscle cells. This happens when not enough oxygen is present. Lactic acid causes a feeling of soreness and pain.",
"Can someone please go in more detail? Or correct me if I'm wrong. It's been a while ><"
] |
[
"If something is being changed over time by Oxygen (and its binding properties), it is oxidized. What happens when Fluorine (a much friendlier element) does the same thing? (What is it called?)"
] |
[
false
] |
Also, are there any really interesting cases of fluoride interactions in daily life?
|
[
"Fluorine has a higher electronegativity than oxygen",
", and is a stronger, more reactive oxidant than oxygen. The term ",
", or ",
" has a specific meaning apart from its association with oxygen:",
"http://en.m.wikipedia.org/wiki/Oxidizing_agent",
"An oxidizing agent (also called an oxidant, oxidizer or oxidiser) can be defined as a substance that removes electrons from another reactant in a redox chemical reaction. The oxidizing agent is \"reduced\" by taking electrons onto itself and the reactant is \"oxidized\" by having its electrons taken away. Oxygen is the prime example of an oxidizing agent, but it is only one among many."
] |
[
"In my line of work we call it fluorination, emphasis on the n for the atom not the ion.",
"In the molten salt reactor experiment when they used H",
"+H2 to create a reduction oxidation reaction it was called the hydro-fluorination process.",
"Its also very acceptable to call it oxidation as well. Oxidation just means when an atom accepts an electron from an atom with an extra valance electron.",
"Also, why do you consider fluorine to be friendly? Its in my opinion the worst industrial (non-rare) element there is."
] |
[
"The idea that it is friendly to other atoms by binding to them often (due to its electronegativity).",
"Especially because it is so friendly that hexafluorides are a possibility."
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary 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!
|
[
"No, the only limit is what you choose to call a \"moon\". Each of the ice particles in Saturn's rings is technically a moon, and there are a squijillion of them."
] |
[
"Yes. In fact, it already is; it's just barely noticeable - although it should be noted that it will oscillate with a period of twice the tides. High tide is when the moon is either overhead ",
" directly opposite, while gravity will be strongest with the moon directly overhead but weakest with it on the opposite side of the Earth.",
"Rough calculations put the current acceleration due to the moon's gravity at GM/r",
" = 3*10",
" ms",
" - 6 orders of magnitude less than Earth's gravity."
] |
[
"It'd probably help if you could link to the particular article you are talking about. People are mostly interested in studying the climate and atmosphere of Mars to understand how it works on Mars, rather than to apply back to earth directly."
] |
[
"If we can find hundreds of exoplanets orbiting stars hundreds of light-years away, why do we have a hard time conclusively confirming Planet Nine within our own solar system?"
] |
[
false
] |
[deleted]
|
[
"That's not an ideal comparison for a few reasons:",
"-There are billions of stars to look at, a small fraction have detectable planets but most of them do not. There is only one sun so we can't get statistics on multiple versions of our solar system.",
"-Most planets are detected by the light they block as they pass in front of their host star. That doesn't work for something farther from the sun than the Earth.",
"-Most planets we detect have very short orbits compared to our solar system, so that periodic signals can be observed. Planet Nine is expected to have an orbit of thousands of years."
] |
[
"We have discovered 56 exoplanets within 10 parsecs. It's likely that there are actually thousands of exoplanets within that distance. So we have only discovered a few percent (perhaps 1-5%) of the exoplanets within 10 parsecs.",
"If there is a 9th planet in our system, then we have discovered 8/9 of the planets in our solar system. That's 89%, which is pretty good.",
"So as you would expect, we are way better at finding planets in our own solar system because they are much closer to us, so they are brighter, and not lost in the Sun's glare. This makes direct observation of these planets possible, unlike all but a few exoplanets. And the methods we use to detect exoplanets (RV and transit, primarily) work best for larger planets closer to their star. Planet Nine would not be detectable by either of these methods if it were an exoplanet.",
"In fact, if a nearby star had a solar system exactly like ours, we would probably have discovered none of its planets yet. Maybe Jupiter if we were lucky."
] |
[
"There are lots of planets, so finding many planets isn't hard. Confirming or refuting the existence of a specific planet is much more difficult, however.",
"Planet 9 is far away, if we knew exactly where it was we could just look at it with a telescope powerful enough to see it (which are unfortunately few) and confirm its existence. But we don't know exactly where it is, we only know generally where it is, so we need to look at all of the places where it might be, over many nights, to find it. And that's a very extravagant use of expensive telescopic resources. Even so, searches for Planet 9 are being performed, but because of the nature of ground based observatories not all of the target area is visible by the observatories on every single night, and not all nights have clear skies, so it's going to take a while to perform all of the necessary observations.",
"As for exoplanet searches they aren't really a good comparison. For one we don't discover those planets the same way (direct detection) we discover them indirectly (via stellar transit or stellar radial velocity variations). Those particular techniques won't work for finding Planet 9 for several reasons, not least of which that they require multiple orbital periods be observed, which would require thousands of years of observations. Additionally, those techniques cannot discover all planets around distant stars, only some of them. We tend to discover the closest and fastest orbiting planets. And we preferentially discover planets that have their orbital planes nearly edge on to our line of sight.",
"Indeed, the vast majority of planets around the stars we have looked for planets around remain undetected, by a factor of 100s. We cannot see Earth-like planets that don't have fortuitously aligned orbital planes. We cannot detect planets that have very long orbital periods (e.g. Saturn and beyond) because we haven't been observing long enough. If we pointed our instruments at a distant duplicate of our Solar System we would have around a 1 in 200 chance of detected Earth and Venus. We would not detect Mars or Mercury at all, most likely. If we observed for decades we could maybe detect Jupiter. Saturn, Uranus, and Neptune would not be detected. And Planet 9 (assuming it exists) would have no hope of being spotted.",
"It's very different being able to detect some planets given that planets are not rare (the haystack) versus being able to conclusively confirm the existence or not of a specific planet (the needle). Similarly, there are lots of rocks everywhere on Earth, you probably see hundreds and hundreds of rocks every day (gravel, natural rocks, pebbles, river rocks, boulders, etc.) But if I were to ask you to track down the location of a very specific boulder that could be anywhere in North America it would be a daunting prospect to do so."
] |
[
"I've heard that humans share 50% of our DNA with bananas. What living organism on Earth shares the LEAST amount of human DNA?"
] |
[
false
] |
[deleted]
|
[
"It's important to realize that the 50% figure refers to actual ",
", not all DNA. A large majority of our genome is not part of any gene, and the same goes for bananas. You wouldn't even be able to compare these non-coding regions in any meaningful sense, since our genomes are about six times larger than those of bananas! Instead, what's being compared is the percentage of the ~20,000 or so human genes that have a corresponding ",
"ortholog",
" in bananas. It's also worth noting that the 50% figure people always quote isn't even accurate, or if it is, it's at least unclear what criteria were used to generate this number. ",
"This article",
" does a good job of explaining this, and also points out that there does not appear to be any reputable source behind the 50% claim. Upon further investigation, the author only finds matches for about 17% of human genes in bananas.",
"As for the organism that shares the ",
" DNA in common with us, it's hard to give a definitive answer since there are so many species without sequenced genomes. However, using the same method outlined in the article above, we can make an attempt at a quantitative estimate. To start, I just picked the organism with the smallest known number of genes (the bacteria ",
", with around 470; ",
"Fookes et al. 2017",
"), and ran it through the OMA orthology database's ",
"genome comparison search",
". The ",
"resulting list",
" contains just ",
" shared across both species, which is very low (fewer than 1% of human genes). But I encourage anyone else to try some other species and see if you can get fewer! It's pretty definitely still going to be a bacterium though."
] |
[
"bananas are Eukaryotes, just like us. This is one of the three most fundamental groups of life that we recognize, alongside Archaea and Bacteria. Eukaryote cells all have nuclei and other organelles enclosed within their own membranes, and that's what we share with bananas. (aside, it's pretty crazy that 50% of our dna is just for getting a basic complex cell to function, right?)\nI think I read that Archaea might be more closely related to eukaryotes than bacteria, but maybe someone with an actual biology degree can answer with more certainty."
] |
[
"I think I read that Archaea might be more closely related to eukaryotes than bacteria, but maybe someone with an actual biology degree can answer with more certainty.",
"Indeed, it is now widely theorized that eukaryotes evolved from archaea. A group of archaea called the \"Asgard archaea\", which were discovered in the deep sea in the last 10 years or so, have been put forth as a missing link of sorts. ",
"Here's an article about it.",
"Part of what makes this a compelling case is that these archaea in particular seem to possess at least some of the genetic machinery* needed to warp their cell membranes around and swallow other cells (",
"phagocytotis",
"). This is a trait otherwise unique to eukaryotes, and indeed it was necessary for eukaryotes as we know them to evolve, given that some of the key organelles in eukaryotes (mitochondria and plastids) evolved from symbiotic bacteria that were probably initially picked up through phagocytosis.",
"*Note: we don't know if Asgard archaea ",
" phagocytose, because nobody has actually seen them. They are, as yet, described entirely from DNA samples from the sea.",
": Oh hey, apparently they have ",
"just recently",
" been ",
"cultured in a lab",
"!"
] |
[
"Does an inductor coil become a capacitor when 1 of the middle loops is cut?"
] |
[
false
] |
It would have no direct path for electrons to cross between the 2 sides of the wire (cut somewhere deep in the coil) so to prevent buildup of static charge the 2 now separate but concentric coils should become oppositely charged, total neutral charge. Do some capacitors work this way? How efficient are they compared to the parallel plate kind? How much efficiency is lost in the transform from inductor to capacitor? What if we put a switch at the break so it could change between capacitor and inductor?
|
[
"It would act like two inductors attached to each side of a very small capacitor. So the capacitor portion would have a huge reactance and you'd very likely end up with a device that had the performance characteristics of an open circuit since the two 'filters' would have an overlapping frequency range."
] |
[
"The physics behind your question is sound, but I have a feeling that the capacitance of these two half-coils would be very small.",
"The rest of your questions would be better answered by an electrical engineer."
] |
[
"The capacitance would be tiny depending on separation distance and surface area on the separation, which would be very small. Ideally a capacitor should be two parallel sheets. "
] |
[
"When I fire a gun does the bullet slide down the barrel, or does it float/fly down the barrel?"
] |
[
false
] |
[deleted]
|
[
"Most bullets are slightly wider than the barrel diameter. For example, the .45ACP bullet is .452 inches in diameter, while the bore is generally (and this varies slightly depending on the gun, and rifling type) .451 inches. The 21,000 psi in the chamber squeezes the bullet into the rifling, preventing gas blow by and accelerating the projectile.",
"To expand, the nominal bore diameter, , for example, .30 cal, is the distance between the lands (high points) in the rifling. In the case of the .308 rifle, the grooves are .004 inches deep, the bullet diameter will be .30 +( .004 x2) = .308in. The bullet will force itself into the rifling, 62,000 psi in the case of this round. It makes a gastight seal. "
] |
[
"In modern guns the bullet is squeezed through the barrel.",
"In the era of muzzle loaded flintlocks and similar firearms the bullet would be smaller than the barrel, in order to be able to be loaded. Sometimes wadding would be added to help the bullet fit more snugly. This is necessary for two reasons. One, if the bullet bounces down the barrel it would be far less accurate. Two, if the bullet does not seal the barrel well then the hot gases from the combustion of the gunpowder will escape out ahead of the bullet and lead to much less efficient propulsion of the bullet.",
"Most modern guns are breach loaded and have rifled barrels. When fired the bullet actually squeezes into the rifling grooves of the barrel, in doing so the bullet is compelled to spin, to keep lined up with the grooves, which creates a gyroscopic effect that stabilizes the motion of the bullet. The exception to this is shotguns, which are smooth bored, in that case a handful of pellets is pushed out of the barrel by the wadding in the shell behind it."
] |
[
"If you notice the last paragraph of that article, jacketed bullets fired out of rifles are almost always larger than the bore and swage to fit."
] |
[
"Are there any languages that are easier or harder for AI systems to sufficiently \"learn\" for translation purposes? If yes, what are the aspects of a language that make the process easier or harder?"
] |
[
false
] | null |
[
"There aren't really individual languages that are inherently more difficult to learn, as the purpose of modern machine-learning is that we automate the process by which we learn the rules. There are some major practical considerations:",
"Furthermore, translation is between ",
" of languages, and there are pairs of languages that are more difficult than others.",
"Edit: I should also say that there's an ongoing shift within the translation community away from the existing strategy of phrase-based machine translation (meaning that phrases are identified and then the statistical translation occurs for an entire phrase, rather than word-for-word). Instead, neural-network based translation tries to learn end-to-end translations, meaning that input text is not broken down into sub-units like phrases or words, but is instead interpreted as a whole and mapped to an output. Google is implementing this strategy for the first time in a real production system, and they've written a paper about it:",
"https://arxiv.org/pdf/1609.08144.pdf"
] |
[
"In Google's instance, one strategy they used to use is they used to train two pairs of neural networks for each language, one for encoding and one for decoding that work with concepts themselves, and then have a common neural network that works across all languages that only deals with the concepts. What they then did is that for any given pair, one encoding network and one decoding network is connected to both ends of the common neural network, yielding very good translation( because it has a dataset the size of the entire common data set and it deals with concepts directly) but also eliminates the need for bilingual datasets and can instead focus on meaning allowing translations between rarely used together languages possible"
] |
[
"Certain languages, particularly artificial languages, have features whereby you can determine the function of the word just by inspecting it.",
"Esperanto is one such language. All singular subject nouns end in -o (-oj for plural). All singular object nouns end in -on (-ojn for plural). All verbs end in -is (past tense), -as (present tense), -os (future tense), -i (infinitive mood), -us (conditional mood) or -u (jussive mood). Adjectives end in -a. Adverbs end in -e. ",
"That's just a basic example, however it makes it very easy for a computer to pick out the relevant parts of the sentence and determine their syntactic purpose, much moreso than a language like English. Is the English \"mail\" a verb or a noun? In noun form, does it mean an item you put into the post, or a type of armour? Depends on the context. In Esperanto, the verb form (i.e.: to send a letter) is ",
", whereas the noun form would be ",
" (and the armour would be ",
").",
"One of the cool things about encoding the grammar into the words themselves is that you can generally write the words in a clause in any order, without changing the meaning of the sentence. This has potential benefits for computer translation, as different natural languages use different words orders (see ",
"this article",
" for examples). Regardless of word order, you can generally translate from any natural language to Esperanto.",
"Work was done in the 80's and early 90's to perform natural language translation by using a modified version of Esperanto as an intermediate form. This has certain conceptual benefits beyond the grammar encoding mentioned above; to translate between n languages, you only need to write 2n dictionaries/rule sets. If you just write the dictionary/rule sets between the various languages directly, you need n(n-1) (or n",
" dictionaries. The first is linear, whereas the latter is exponential.",
"FWIW I'm to aware of anyone who is practically using this now, except for services that provide a direct translation to and from Esperanto itself (like Google Translate). And there are other natural languages that include part or all of their grammar encoded into words and sentences (Turkish, for example). However, features like this do make it easier for a computer to determine the syntactic function of a given word in a sentence, potentially providing for better translation opportunities."
] |
[
"How does a dried, packaged seed \"know\" when to grow once I've planted it in the ground?"
] |
[
false
] |
[deleted]
|
[
"http://www.ehow.com/about_6695705_respiration-germinating-seeds.html",
"Respiration begins when a seed absorbs water. The enzymes inside seeds have to be in suspension to function. Activated enzymes start respiration and use organic matter stored in the seed during respiration to make ATP molecules needed for growth. Respiration continues in the seed after the sprout has emerged until the seed’s endospermic material is used up and the cotyledons have produced the sprout."
] |
[
"So are said enzymes in the ",
"germ of the plant",
"? "
] |
[
"Imbibition (\"drinking\" or absorption of water) is part of it, but many seeds also have complex germination inhibition systems in place. Some seeds require stratification (to be sown in cold, wet soils over winter, for example) that \"burn up\" various germination-inhibiting compounds. Others require scarification, which means the seed coat must be physically damaged in order to allow water to enter.",
"One of the classic scarification seeds is the lotus, which has a very hard testa. Normally this seed coat can be physically abraded away with a little work and a file; it is dropped into water, and quickly (within 2-3 days) will swell enough to split the seed, and allow the cotyledons to emerge. Other seeds require heat, either to be released (from pine cones, for example), or to be physically \"cracked,\" allowing water to enter and the seed to germinate."
] |
[
"Is every Subatomic particle moving at the speed of light at all times?"
] |
[
false
] |
Ive wondered this for a while now. This question only includes smaller subatomic particles and not matter.
|
[
"No. Only things without mass, like photons, can travel at the speed of light."
] |
[
"There are several kinds of neutrinos. We observe that they change between these kinds. Therefore the neutrinos must experience time, so they can't be traveling at the speed of light - so they have mass."
] |
[
"Massless particles have to move ",
" the speed of light.",
"Massive particles have to move ",
" the speed of light.",
"So no massive particles are moving at the speed of light, and most of the subatomic particles we know of are massive, including quarks, electrons, and various other things which make up most of the stuff in the Universe. Conversely, the mass",
" particles - photons being the most famous - are going to move at the speed of light and can't choose to do any differently."
] |
[
"If I had a treadmill set at a 5% upward grade and someone ran on it for a mile, would they be expending the same amount of energy running up a perfectly straight track that is angled at a 5% grade for a mile?"
] |
[
false
] |
It seems like it is the same, but the problem is that if you take the initial and final state conditions, the person running up the track has gained some potential energy, the person on the treadmill has not moved.
|
[
"Even when we run outside we are still on a treadmill, it's just that we are going the same speed as it and we call it Earth. There isn't enough room on a treadmill to travel the same speed as the belt (if the belt were 10 miles long you would eventually feel no movement as you stood there and you could take off running as normal). This means that the belt is always pushing your legs back as you bound up and down - basically, a treadmill can never accurately recreate running outside.",
"None of this makes sense to me. Can you please try explaining it in a different way?",
"The only difference I can see between running on a treadmill and a stationary (relative to Earth's surface) treadmill surface would be the movement of the air relative to you (where running on a treadmill would be like having the wind blowing in the direction of your movement at the same speed of your movement during a non-treadmill run)"
] |
[
"For a treadmill to accurately simulate running it would need to have a feedback response that can adjust speed to exactly counter your forward movement in a natural way. If you could confidently start sprinting on a treadmill and the belt would move at that exact moment to compensate then you would be using the same amount of energy as running outside. This would be like standing still on a 10 mile long treadmill traveling at 5 miles per hour and then running opposite the belt. You would eventually have no movement relative to the ground yet you began running on your own accord. You can say that when up to speed and neglecting wind resistance a treadmill is accurate. To relate this to gravitational potential energy a section of running time must be taken from the middle where there is NO change in speed in either running scenario. The treadmill runner would also need an large fan providing equivalent wind resistance. In this scenario you could say that the gravitational potential energy gained by the outdoor run at a 5% grade must be equivalent to a certain energy given to the machine at the same 5% grade. The equivalent energy is transferred to increased belt friction, motor and other mechanical resistance. Yes the ways in which the treadmill and outdoor run may be subtle (wind being the largest) but they can change the outcome of a problem like this. "
] |
[
"You're right. It's misleading. I got off track relating it to a gravitational problem. What I should have said was yes but only in specific circumstances beyond just wind. I'll edit."
] |
[
"I just learned about the sinoatrial node. Why does the heart stop in cases like fatal brain aneurisms if the heart has its own pacemaker?"
] |
[
false
] |
If I understand correctly, the sinoatrial node is sort of like a natural pacemaker that generates an electrical impulse and stimulates the heartbeat. I read that even if you separate the heart from the brain, the heart can keep on beating because of the SA node. What is the reason that, for example, in the case of a fatal brain aneurism the heart stops working? Or a broken neck, traumatic head injury, or any number of other things that can kill someone without physically damaging the heart or causing huge amounts of blood loss. Why does the SA node stop stimulating heartbeat in these cases? Am I just misunderstanding the concept?
|
[
"Not a pathologist, but I think it goes something like this:",
"In a brain aneurysm, the leaking blood is pumped into the space between the brain the skull. This puts pressure on the brain and the vessels delivering blood to the brain, reducing blood flow to the brain. This causes the brain cells to die. If the medulla oblongata dies, your brain stops telling your abdominal muscles to breath. Once that happens, it's only a matter of time before your heart stops due to lack of oxygen.",
"Basically the brain controls breathing, and if breathing stops the heart runs out of oxygen to continue pumping."
] |
[
"In cases of ",
" as with (in your example) massive aneurysmal subarachnoid hemorrhage, trauma, or other causes, the heart loses its greatest ally in the cause of controlling cardiovascular system function.",
"Normally a combination of sympathetic and parasympathetic inputs to the heart and to the circulatory system along with neuronal and hormonal inputs elsewhere help regulate cardiac output, systemic resistance, and volume. Antidiuretic hormone levels set by the posterior pituitary help regulate volume and ionic balance. Thyroid hormone released secondarily due to TSH secretion from the anterior pituitary can help regulate heart contractility and energy use.",
"Without pituitary hormone release, inotropic action on the heart is depressed, fluid volume decreases due to diabetes insipidus, and systemic resistance decreases from loss of autonomic innervation. The heart is left in a state in which it certainly ",
" continue to beat regularly with an intact SA node, but in which its ability to intrinsically regulate circulation is low. Starling's law continues to operate but otherwise the heart is at risk of succumbing from a vasodilatory and hypovolaemic circulation and metabolic abnormalities.",
"This is not to even mention the transient bradyarrhythmias from Cushing's response during the onset of brainstem herniation, nor the transient tachyarrhythmias resulting from catecholamine release during destruction of the medulla oblongata.",
"Pathophysiologic Changes after Brain Death",
"Irwin and Rippe's Intensive Care Medicine"
] |
[
"Because the heart also needs other things to function, such as nutrients, and getting adequate quantities of nutrients into your body requires a complex system of actions that involve your brain and digestive system. Similarly, elimination of waste products requires a functioning brain, liver, and kidneys.",
"If you bypass it all with machines, we can maintain a human in a vegetative state for years."
] |
[
"What happens to the muscle and bone when a finger is jammed?"
] |
[
false
] |
Are they sprains or strains and what does it "look like" on a muscular/skeletal level? Bonus question: Why do I feel the need to pop the finger ever 30 seconds to a few minutes? When they are uninjured I pop them maybe 4-5 times a day.
|
[
"There aren't any actual muscle groups in the fingers themselves like you have muscles resting on your arm that bends your elbow. All the muscles that control the fingers are found in your forearm. Each finger has two groups of tendons extending from the forearm, through the wrist, and onto each finger bone. Imagine each finger is a puppet and they are pulled by muscle groups on each side of your forearm. Coordination on the keyboard to type is determined by a few precise muscle twitches on your forearm. Amazing isn't it? ",
"When fingers jam the joints between each bone becomes compressed due to something pushing the finger bones so hard. A strain of the finger muscles would be felt more at the wrist rather than on the fingers themselves. Such as carpal tunnel. ",
"As for the need to pop your injured finger it's most likely a habit. Popping my previously injured fingers feels a lot better than popping the healthy ones. "
] |
[
"The space in between each finger is put under a lot of pressure. There are nerves, blood vessels, and connective tissue in joints. So the swelling is the result of the crushed vessels and the tenderness is from the nerve cells being cramped up by the large increase in fluid in their tissue. The fluid is a mix of blood and damaged cells. When cells die they attract the white blood cells responsible for recycling dead cells and their materials.",
"Recovery it depends. I'm an ER nurse, but I've seen a few jammed fingers come and go. If the finger is jammed to the point, the finger is broken, bent to a very unnatural position, or sidewards then you might need a hand surgeon to take a look, ussually they put on a cast or other device for fingers. But if it's a simple compression to where it's swollen and tender then just follow the acronym RICE. and gradually rehab your finger at home by slowly using it again after resting it."
] |
[
"My mistake, it's been years since my anatomy and physiology class. Thank you for catching that. I think there might also be muscles in between each metacarpal. "
] |
[
"Why do we use sine to calculate refractive index?"
] |
[
false
] |
In class today I learnt about refractive index. We only got as far as a practical and learning the equation (n = sin(i) / sin(r)). I understand why we would need to calculate refractive index, but I don't understand why we use the sine function in the equation. I always thought sine was a wave, so if anyone can explain this to me I would be grateful. Edit: Spelling mistake
|
[
"The sine function gives a wave when plotted in a graph, but it is also the ratio of two specific sides of a triangle for a given angle. The calculation for refraction index uses the second usage of sine. "
] |
[
"Snell's law can be derived from Fermat's principle or Huygen's principle (or a few other ways I'm sure, but I've only had geometrical optics).",
"The definition of the refractive index of a medium is",
"n = c/v",
"Where c is the speed of light in a vacuum, and v is the speed of light in that particular medium. ",
"Huygen's principle states that, on the wavefront of light, every point can be seen as a little point source of waves, where their collective interference causes an effective plane wave. Drawing these wavelets on an interface between two materials leads to ",
"this image",
".",
"The distance between the parallel green and red lines in this image is the wavelength of light in the medium, λ. If you draw two right-angled triangles like in ",
"this shittily drawn image",
", you can use SOH to write two relations:",
"sin(i) = λ1/d -> d = λ1/sin(i)",
"sin(r) = λ2/d -> d = λ2/sin(r)",
"For a wave, the wave speed is the wavelength times the frequency: v = λf. Equating the above relations and inserting λ = v/f:",
"(v1/f)/sin(i) = (v2/f)/sin(r) -> v1/sin(i) = v2/sin(r)",
"Using the definition of the refractive index:",
"(c/n1)/sin(i) = (c/n2)/sin(r)",
"n1*sin(i) = n2*sin(r)",
"The refractive index of air is usually taken to be 1, so inserting n1 = 1 yields your familiar high school formula."
] |
[
"or a few other ways I'm sure, but I've only had geometrical optics",
"If you want to be really fancy about it, you can derive Snell's Law from the boundary conditions on Maxwell's Equations as well (and the law of Reflection, and about all the rest of optics; that derivation was when electrodynamics really \"clicked\" for me)."
] |
[
"Why is Haloperidol absorbed more slowly in individuals with Schizophrenia?"
] |
[
false
] |
So I was reading about some anti-psychotic drugs since I'm not in the medical field and didn't get a joke my friends told, but just read that Haloperidol is absorbed much more slowly in individuals with schizophrenia. This really got me wondering if that had anything to do with Schizophrenia directly or if had more to do with the fact that 50% of schizophrenic cases are heavy users of drugs and alcohol. What specifically about Schizophrenia would cause this?
|
[
"I'm having trouble finding a primary source with that information, but ",
"this paper",
" did a retrospective analysis on a related drug (paliperidone) and found that the pharmacokinetics were influenced by patient BMI, injection site, injection volume, needle length, and creatinine clearance. So it could be due to variations in methodology regarding one or more of those. I'm not sure if BMI or creatinine clearance are significantly altered in schizophrenics specifically, but if they weren't controlled for in whatever study was done to find the difference in Tmax, then it could explain the differences as well.",
"Aside from that, I'm not sure what could cause that. Sorry for the lack of concrete answer."
] |
[
"Actually I'm at work right now and there aren't any psych consults to see so I'm looking at our med search to see if I find anything.",
"Only thing I really see is that oral dose is initially higher for schizophrenia then acute psychosis according to manufacturer label. ",
"IM as decanoate is available that is a monthly injection but that shouldn't effect absorption besides what it intended to as a monthly injection. ",
"Edit: OK so I've checked medscape and lexicomp and neither differentiate peak time. Medscape says 30-60 min whereas lexicomp says 20 min for IM. Will check my drug reference book when I get home. I'm beginning to suspect a wiki error or reference to a study that's not cited.",
"I was a davis drug guide fan and wife was a Mosbys so I checked both we had laying around and neither differentiate between healthy and schizophrenic patients."
] |
[
"Actually I'm at work right now and there aren't any psych consults to see so I'm looking at our med search to see if I find anything.",
"Only thing I really see is that oral dose is initially higher for schizophrenia then acute psychosis according to manufacturer label. ",
"IM as decanoate is available that is a monthly injection but that shouldn't effect absorption besides what it intended to as a monthly injection. ",
"Edit: OK so I've checked medscape and lexicomp and neither differentiate peak time. Medscape says 30-60 min whereas lexicomp says 20 min for IM. Will check my drug reference book when I get home. I'm beginning to suspect a wiki error or reference to a study that's not cited.",
"I was a davis drug guide fan and wife was a Mosbys so I checked both we had laying around and neither differentiate between healthy and schizophrenic patients."
] |
[
"Why Fluorine is a Hydrophobic compound ?"
] |
[
false
] |
[deleted]
|
[
"It has a strong ability to withdraw electron density from what it bonds with. In the case of Teflon (or PTFE), you have a situation where two fluorines are symmetrically bonded to one carbon; both the fluorines are pulling the electrons towards them equally strongly. This limits the electrons' availability to take part in dispersion interactions.",
"Dispersion forces (or London forces) are electron fluctuations that occur in unison. I dunno, the best way to describe this would be to imagine a room full of people with their hands in the air, with everyone moving them from left to right, left to right all at the same time. This movement from left to right and back represents a changing dipole. A dipole means there exists polarity. Water is polar and it is attracted to polar material (or rather, it ",
" polar material).",
"So, in PTFE, having fluorines pulling electrons equally in opposite directions restricts the outer electrons' ability to take part in London interactions.",
"I the case of some other non-stick material, because of fluorine's strong electronegativity, it pulls electrons away from something that would otherwise be quite reactive."
] |
[
"Well, you're comparing apples and oranges there. It's not the Mg-F or Mg-O bond that's important here; it's the additional O-H bond, which is a polar; water, being polar, will naturally be attracted to it."
] |
[
"Well, you're comparing apples and oranges there. It's not the Mg-F or Mg-O bond that's important here; it's the additional O-H bond, which is a polar; water, being polar, will naturally be attracted to it."
] |
[
"[Biology] Why do we sleep better with the lights off then with the lights on?"
] |
[
false
] |
Is this a obtained preference or does this go back to when we slept outdoors during the night or in caves?
|
[
"We produce melatonin from our pineal gland when its dark. It regulates our sleepfulness/wakefulness. Yes it has everything to do with our baser human instincts, as does every aspect of our lives. ",
"We are animals pretending to be above organic lifeforms, but alas, we are still animals."
] |
[
"You also partially open your eyes at times like during REM cycles. REM=Rapid Eye Movements. You go through different stages of sleep. Each cycle lasts about 3 hours. Wearing an eye mask or room darkening curtains helps with this for day sleepers."
] |
[
"This is all due to our evolutionary ancestors who had a pineal eye instead of a pineal gland. The pineal eye has photoreceptors that help regulate the sleep/wake cycle and assist in managing internal body temperature. Our ability to sleep better at night is a holdover from \"lower\" animals. Melatonin and cortisol wane and wax based upon our conditioned sleep/wake cycle. "
] |
[
"Saturation: is it possible to saturate water with several substances?"
] |
[
false
] |
For example, let's say that the saturation point of sugar in water is 50g, and salt is 100g. If I were to dissolve 50g of sugar in 1l of water, how much salt could I add? Is it the full 100g, or is it less?
|
[
"I'm not entirely sure about this example, however adding impurities in your solution can interact with whatever you are trying to dissolve and make them more soluble. "
] |
[
"Sugar does not \"dissolve\" in water but it forms several equilibriums:",
"http://users.wmin.ac.uk/~perryd/ch/glcrings.gif",
"So, what's the effect of salt saturation on a water glucose solution you may ask.",
"Simple, since glucose just make an equilibrium with water while sodium chloride in fact \"dissolves\" or splits in ions the effect is that water will have to coordinate na+ and cl- ions.",
"As you can see sodium chloride needs a lot of molecules to be coordinated by water and stay separate:",
"http://piercecollegeweather.com/img/ci-na+.jpg",
"What's the effect on glucose?",
"The effect on glucose is that you wil have less H2O molecules available to make the water-glucose equilibrium.",
"Same applies to sodium chloride, the effect of glucose presence shifts the equilibrium to reagents a bit ( so NaCl <-> H2O) more then when you have only NaCl.",
"So the effect of adding substances to water is that any of them \"steals\" more or less water from the other reaction.",
"Actually calculating exactly the equilibrium between a saccaryde and a salt in water is not completely easy since they are not both salts but for your reaction we can easily say that they are both \"dissolved\" ( I repeat glucose does not dissolve, but just to let you understand..).",
"But don't forget that the equilibrium is extremely slow so if you wanna try adding 50g of glucose and 100 g of salt in water you may wait a lot at 300K. "
] |
[
"Reasonably good explanation of ion activity and salting out effect and their effect on solubility. For point of clarity - glucose does dissolve, it just doesn't do so by ionization like acids, bases and salts. Rather it does so by hydrogen bonding - the same type of reaction that water has with itself. Further, unless you are talking about some really extreme pHs, glucose will not form zwitterions (you show glycine, which is an amino acid, not a saccharide). Were zwitterionic forms a significant contributor to glucose solubility, you would still know max solubility, but you would have to state a pH at which you were performing the experiment. In that case, the solubility would be driven by ionic forces as well as hydrogen bonding."
] |
[
"Is there any evidence to suggest that galaxies are just young super-massive \"solar\" systems?"
] |
[
false
] |
While looking at the formation of solar systems and the current state of galactic formations I noticed that they both appear to form similarly from dust and particles eventually combining around a large gravitational object at the center. Could galaxies just be young super-massive "solar" systems so-to-speak? Obviously they wouldn't be called solar systems since the gravitational center would be based around a super massive black hole. However, are there any physical limits on the size of planets/stars? Such as the core becoming too compressed by the mass of the entire object? tl:dr version- Given enough time, could the Milky Way or other galaxies form massive "solar systems" around a super-massive black hole at the center with revolving bodies being roughly the equivalence in size to VY-Canis Majoris? Edit for clarity: Our galaxy still has a vast amount of cosmic dust. Given enough time (in the neighborhood of billions to trillions of years), would that clear away and form a more solar system-esque structure. In my mind it looks like our current solar system but with a super-massive blackhole where our Sun is and orbiting that would be billions of stars, some as large as VY-Canis Majoris and some just the size of a white dwarf, with trillions of moons surrounding those. I suppose a somewhat condensed, cleaner and more structured/organized galaxy is what I'm trying to represent as the image.
|
[
"I don't understand what you're asking really.",
"Imagine it this way: the moon orbits the earth, the earth orbits the sun, the sun orbits the black hole at the center of the Milky Way, and the galaxy orbits the center of mass of the local galaxy cluster. That's the way things are. ",
"Are you asking if all the stars will collide together to form bigger stars? Well some will, yes. We have binary star systems. Sometimes stars spiral into each other, siphoning off each others' plasma. ",
"But not all stars will crash into each other. They are just too far apart. Just like earth will never crash into Jupiter (within the foreseeable future), just like Jupiter's moons don't crash into each other anymore. "
] |
[
"Sorry for the lack of a straightforward question. What I'm trying to ask is that given enough time (on the scale of billions to trillions of years) if all the solar systems within a galaxy would roughly form into a large, multi-billion planet, macro solar system with the black hole at the center. Given the time it took to form ours, I find this to a be a reasonable conclusion."
] |
[
"all the solar systems within a galaxy would roughly form into a large, multi-billion planet, macro solar system with the black hole at the center. ",
"That's what we already have.",
"Unless you mean, will all the stars burn out and all the planets stop orbiting stars and just orbit the block hole? I don't think so. Even in solar systems where only a white dwarf remains, planets can still orbit the white dwarf pretty much forever. That's because the white dwarf still has mass, the planet still has mass, and they each still have their respective angular momentum. The same goes for moons orbiting a planet."
] |
[
"If you stacked a lot of microscopic organisms, would you eventually be able to see them? What would they look like?"
] |
[
false
] |
Assuming they don't move or run away, what would happen if you stacked (or piled up) a of microscopic organismic or just microscopic "things" in general. Disregarding the improbability/impossibility of finding that many of the organism, would you eventually pile up enough to be able to see them? Would it look like a solid mass? Bonus: what would it feel like?
|
[
"This actually happens all the time, especially in labs when you're growing up a culture of bacteria to use for something. ",
"And you can definitely see them!",
"What they look like depends a lot on what species of organism it is and what environment it's growing in. A lot of bacteria will be a kind of gooey snot-like solid, for example, but a lot of mold ends up looking like a furry powdery substance (you've probably seen this before on bread or forgotten food in the back the fridge). ",
"Most cells are kind of whitish by themselves, but a lot of species also make pigments (they can't see them, but some of the substances they use for photosynthesis, chemical warfare, etc happen to be colorful to us). ",
"Grand Prismatic Spring in Yellowstone",
" gets its colors from the microorganisms that live in it."
] |
[
"So mold is basically what the original post was talking about? Aren't we all giant 'stacks' of microscopic bacteria?"
] |
[
"Well, not bacteria. But stacks of microscopic cells would be accurate. Bacteria is just a particular type of cell."
] |
[
"What exactly can quantum computers do?"
] |
[
false
] |
I know they're based off of quantum mechanics, but I'm a little unsure about their purpose. Are they able to replace modern computers or are they being sought after primarily as an instrument?
|
[
"I will answer your question after a few paragraphs of background. Yay learning!",
"Computer scientists have a theory of complexity with various complexity classes. We take some problem (such as \"what are the factors of this number?\"), and classify it according to properties of some algorithm known to solve it. For instance, the above problem can be computed in what's called exponential time: the number of steps required for a number of length n is bounded by some exponential function. Thus, it is in the class EXP.",
"What's interesting in this case is what problems are ",
", or can be solved practically. The common standard for this is polynomial time computation (as above, this means the number of steps required is bounded by some polynomial), which is represented by the class P. It turns out that due to the way quantum computers work, you really need to consider the class BPP, containing problems that can be solved in polynomial time by a ",
" algorithm, where the algorithm can return wrong answers with probability at most 1/3. But this turns out not to be a huge problem. You can get arbitrarily high certainty by just running the algorithm repeatedly and checking how many of the answers agree, and this among other things has most computer scientists convinced that every problem in BPP is in P.",
"Now, why are quantum computers important? They have their own \"tractable\" class associated with them. It's called BQP: the definition is the same as for BPP, except your algorithm gets to run on a quantum computer. And it's considered highly unlikely that every problem in BQP is in P. So if the suspicions of computer scientists are right, there are things quantum computers can do efficiently that classical computers cannot.",
"But what's more important right now is that quantum computers provide efficient algorithms for problems that don't have any others. Specifically, integer factorization is known to be efficient with a quantum computer. This is a huge deal, because the most common forms of secure encryption today rely on the assumption that you can't do that. It's still not going to be fast, and it's doubtful we'll ever have quantum computers large enough to make it fast enough to be useful. But if we ",
"... obviously, things becoming insecure is a big deal.",
"Again though, we're probably never going to have large scale quantum computers, for the simple reason that keeping large quantum systems coherent is soul-crushingly difficult. Even if engineers rise to the challenge, they're going to be too sensitive to the environment to be used even as lab instruments. You certainly wouldn't be able to expose one to the dust under your desk.",
"So tl;dr: they're theoretically very useful. But it's unlikely anyone will have a big one, and you or I certainly won't."
] |
[
"They can do precisely the same things classical computers can. Further, they'll have less memory, and each operation will be much slower.",
"So why would people be interested? Because while they're slower and smaller, they can do some things with many fewer ",
"-operations and ",
" bits than we can do with classical operations and classical bits. Computer scientists like to talk about the hardness of problems based on how they \"scale\": how hard parameterized problems become as they get bigger. A classical computer can simulate a quantum computer, but it \"scales badly\". Each additional qubit that a quantum computer has basically doubles the size of the problem of simulating it for the classical computer.",
"What sorts of things are they good at? Well, physicists are interested because they are good at simulating quantum systems, which classical computers are bad at. The NSA is throwing money at them, because there are a couple of cryptographic systems that can be broken by quantum computers. It's hard to factor the product of two large primes classically, but it turns out that we can actually take advantage of some hidden symmetries of multiplication to get the quantum computer to factor more efficiently, by using a Fourier transform."
] |
[
"Sure. There's a set of problems that we can solve efficiently with a classical computer, and a set of problems that we can solve with a quantum computer. There are problems that we know are in the latter set which we do not know are in the former set. This means that there are problems we know how to solve efficiently with a quantum computer, which we do ",
" know how to solve efficiently with a classical one. One of these problems is factoring an arbitrary integer: it's the primary reason why any of this is interesting to laymen, because efficient factorization breaks the most common cryptography algorithms used today.",
"If you want me to elaborate on any details, ask away, but that's the important part."
] |
[
"Does the amount of salt in water effect the time it takes to evaporate?"
] |
[
false
] |
like, does more salt make water take longer to evaporate?
|
[
"Yes, all things being equal . This is mostly due to the ",
"colligative property",
" of boiling point elevation/vapor pressure depression. It's important to keep in mind that when you're trying to predict the rate (kinetics) of a physical process, ",
" things can be a factor. Generally, rate of evaporation will scale with vapor pressure. Other critical factors are the ambient temperature and the rate at which unsaturated gas mixtures (air) is circulated over the solution. In this example, if you blow dry air over the salt water solution, it will evaporate faster.",
"Another \"real life\" type of detail that can affect how fast this solution evaporates would be if a solute crust forms as the solution evaporates and concentrates the solute past the saturation point. The crust would decrease dry air access to the solution surface, decreasing evaporation rate."
] |
[
"Yes, because",
"1) some of the heat energy is absorbed by salt ions, which do not evaporate",
"2) water-salt interactions are stronger than water-water interactions, so as the amount of water decreases, the strength of adhesive forces keeping water molecules in liquid phase increases",
"3) water only evaporates on the surface. If some of the surface area is occupied by salt ions, the number of water molecules escaping per second decreases",
"Could be some more factors that I couldn't think of now."
] |
[
"Yep, like other people have said. It's not a particularly strong effect for amounts of salt you're likely going to run into. So it takes a pretty careful measurement to really notice the difference. you're not really going to notice it very much in normal life."
] |
[
"Why didn't the Greenland ice sheet melt after the ice age?"
] |
[
false
] |
Part of the Greenland ice sheet is at the same latitude as where the ice sheets that covered Canada and northern Europe were and those melted, so why not the Greenland one?
|
[
"Jet streams. The earth isn't a static thing, hot air is blown via jest streams across the globe, cooled and recycled, like an AC.",
"Greenland wasnt getting an equatorial stream north, the air that hit europe ice cooled the air, and warmed the ice, causing it to melt over a few thousand years.",
"That loss of cooling changed the earths temp, and slowly started warming, which caused a shifting jet stream over 5,000 years, and giving us a more current wind model today"
] |
[
"There's also the Gulf stream, north Atlantic drift, and Labrador current. the Gulf stream bring warm water up the eastern seaboard, turns out into the Atlantic at the boundary between it and the Labrador current, and the goes across the ocean to warm much of Europe. The Labrador current brings cold Arctic water south, cooling Greenland and the waters off the Atlantic coast down to Massachusetts."
] |
[
"You can't equate latitude directly with temperature, due to jet streams and ocean currents. The ",
"Gulf Stream and North Atlantic Drift",
" bring warm water (and accompanying air masses) to Europe and along much of the coast of North America. Note in the image that Greenland is bordered almost completely by a cold current from the pole instead.",
"These ocean currents can have a huge impact on nearby land climate. London England is 51deg north and the coldest month's average low is 5C (41F). That's farther north than Winnipeg Canada at 50 deg north, where the coldest month average low is -21C (-6.5F)."
] |
[
"2 part question here: First, how does a black hole become charged? And second, why do some rotate but others do not?"
] |
[
false
] |
Basically, I just want to know what the mechanism behind "charging" a BH is, because I thought that all matter was ripped apart to the quark level or whatever. How does is gain a charge? And what causes some to rotate but not all of them?
|
[
"Just toss electrically charged matter into it so that it gains a net charge. If you initially have an electrically neutral black hole, perhaps made by the gravitational collapse of an equal number of protons and electrons, then just shoot an electron beam at it. By conservation of charge the charge of those electrons is now the charge of the black hole. "
] |
[
"Most black holes probably rotate—",
"some even near a fundamental maximum",
"—because the stars that produced them rotated and angular momentum is conversed in all of physics. A rotating black hole is a strange beast with some truly bizarre properties."
] |
[
"All black holes rotate. Some rotate more than others, but everything rotates a little, and when you compress it that much, it will start rotating very fast. We study non-rotating black holes because the symmetry makes the math easy, not because they're a thing."
] |
[
"Does wind have the same effect on light that it does sound? Why or why not?"
] |
[
false
] |
We've all heard that wind can interfere with and even direct sound waves, but if all that's true then why wouldn't wind affect light? "Light is both a particle and a wave." Okay, well we KNOW that wind can carry particles . . . And if wind can carry a sound wave, why not a 'light wave'? Forgive me if this a stupid question...
|
[
"The main difference is that the gas particles carry sound waves, while light is a propagating electromagnetic wave that travels ",
" the medium, and not ",
" the medium.",
"The only way that there would be a visible effect by wind would be if it somehow changed the refraction of the air, like in a ",
"mirage",
", but my guess is that wind acts to homogenize the air, so there shouldn't be any noticeable effect."
] |
[
"so the mistake you are basically making is thinking that by 'a particle' the person means is like a ball that you can pick up and throw around. ",
"what they in fact mean when referencing wave/particle duality is that it doesnt follow the rules of the macroscopic world. ",
"when you look around yourself in the 'real' world things act in basically 1 of 2 ways, either like a particle or a wave. the best way most people can understand the difference here is when a ball or a brick, or a t shirt passes through a gap, it just keeps on going. but when a wave of water passes through a gap it makes a new ",
"wave pattern that looks pretty cool",
"but when we look at things on the very small scale, electrons and photons and similar, their behaviour doesnt fit either of those 2 categories. depending on the situation they sometimes 'act' like particles, and sometimes like waves. so the shorthand way of saying that is wave-particle duality.",
"so getting back to your question, you are expecting light to act like pollen or dust in the wind, to be knocked about, but that isnt the case, light is not a particle in the classical sense and understanding. now as ",
"/u/xenneract",
" explained above there could possibly be some measurable interaction because lights travel is not instant, but i dont think thats really what you were getting at."
] |
[
"Light is infact perturbed by air currents, just usually not enough to notice. When using an optical interferometer for example, if you clap or breathe near your photo detector the intensity signal will oscillate up and down as the laser source becomes unalligned and realligned with the semi conductor.",
"This is due to the fact that the perturbation changes the density of the air, and thus changes the refractive index, causing the beam to refract."
] |
[
"Is there definitive scientific evidence that the universe is, in fact, infinitely expanding?"
] |
[
false
] |
Hope it's not a dumb question.
|
[
"There's clear evidence that the expansion is happening and that it's accelerating. ",
"If we assume this will keep going then eventually all galaxies become isolated from each other and something like a ",
"heat death",
" occurs. ",
"But no one knows if the expansion will keep on going. We don't even have a good theory for the acceleration yet."
] |
[
"Didn't know the indefinite expansion was related to the maximization of entropy. Is it really related? I thought it wasn't."
] |
[
"It's not connected, it's just a side effect if you wait long enough. ",
"In an eternally expanding universe the energy density just keeps dropping, causal domains becomes smaller and smaller and everything cools and stop interacting eventually. We asymptotically approach absolute zero.."
] |
[
"How are thermodynamic quantities calculated? Such as enthalpy, internal energy, entropy, chemical potential, etc."
] |
[
false
] | null |
[
"This is a good question. Here's the general procedure for simple thermodynamic systems:",
"First you start by defining your ensemble. What are you dealing with, what are your independent variables, what's being held constant, etc. For example, you might say that you have a box of gas where your independent variables (the knobs you turn) are the volume and the temperature. And you say you want to study your system at equilibrium, so you allow the gas to reach thermal equilibrium with an external system at temperature T. This is the ",
", just as an example.",
"Then you dive into statistical mechanics and begin counting states. Yes, literally counting. For systems with a finite number of states, you can count them on your fingers. For continuous spectra, you integrate over phase space (combination of 3N-dimensional coordinate space and 3N-dimensional momentum space).",
"The quantity you're trying to get by counting all these states is called the ",
". For systems with discrete spectra, you just sum over all energy levels (denoted by i) the quantity:",
"g",
"exp[-βE",
"], where β = 1/kT, and g is the degeneracy (number of quantum states with this particular energy).",
"For a system with a continuous spectrum, you integrate",
"exp[-βH] d",
"x d",
"p over the entire 6N-dimensional phase space for your system, where H is the Hamiltonian for your system.",
"Once you have the partition function, you can get pretty much any thermodynamic quantity you want from it. For example, the average internal energy is:",
"E = - d(ln Z)/dβ, where Z is the partition function, and the derivative should be a partial rather than a total.",
"This gives you the average energy as a function of beta, which is essentially just temperature.",
"The typical way to proceed from here for the canonical ensemble would be to find the Helmholtz free energy:",
"F = - kT ln(Z).",
"Then the entropy is just:",
"S = - dF/dT, where the derivative is a partial.",
"The chemical potential is:",
"μ = dF/dN.",
"The pressure:",
"P = - dF/dV.",
"Then the Gibbs free energy is:",
"G = F + PV. We found F and P above, and V is a variable that we control, so we know everything we need to know to calculate G if we want it.",
"The enthalpy is:",
"H = G + TS, again we know everything we need.",
"Then to go further, we can get things like the heat capacities, thermal expansion coefficients, compressibilities, the speed of sound, whatever.",
"So starting with counting states and finding the partition function, we get all the quantities of interest in equilibrium thermodynamics."
] |
[
"To give a slightly more compressed answer.",
"The way we go about calculating various thermodynamic variables is by relating them back to quantities we can readily determine. For instance variables we can easily measure in a system are things such as pressure, temperature, volume, etc. ",
"So what we do is find the relationships between those variables and other thermodynamical variables such as the enthalpy. For instance the relation between temperature and the enthalpy is the heat capacity of the system. ",
"By creating a network of relationships we can figure out the variable we need from the variables we know. "
] |
[
"It is conceptually simpler to start from statistics: start with the multiplicity Omega of macrosystems. Two systems with the same temperature have the same relative change in Omega with internal energy. Entropy is proportional to log Omega."
] |
[
"The electromagnetic field is one where the electric field is 0 but the The Higgs field has a non-0 value everywhere. What does that mean? It's an energy field with constant charge?"
] |
[
false
] | null |
[
"It's simpler than that.",
"The the level of water on a swimming pool. This is a field, it's a number that takes some value everywhere on the lake. If you have a windy day, this number can change very dramatically because you can have waves forming, but if you average out the waves, you have something which is the expectation value of the field, which is the level of the pool on a sunny day with no wind or kids jumping around.",
"You can change the level of the pool by opening a hose on it and letting water flow. In a world without friction, if you just open and close the water source in a tiny fraction of seconds, you will a localized flow of water propagating through the swimming pool. And if you have a drain, this flow of water can just propagate until it reaches the drain and is reabsorbed.",
"The electric field has a 0 expectation value, which means that it corresponds to an empty swimming pool. Whenever you wiggle around a charged particle, it's as if you opened a hose on the field, you create a localized excitation (the photon), and it travels until it is absorbed somewhere else. ",
"The Higgs field is like a swimming pool filled with water. You can create a localized excitation on top of it, but if you average out these excitations, the expectation value is still non-0. ",
"So yes, the vacuum of the universe is filled with this invisible matter that is constantly interacting with everything that is."
] |
[
"where the electric field is 0 but the The Higgs field has a non-0 value everywhere. ",
"This is not a description of an electromagnetic field. It is a description of the field configuration that makes up the (classical) vacuum."
] |
[
"is the \"expectation value\" a number that represents energy?"
] |
[
"Help me reddit! Wondering why water always feels colder than the room temperature. Wet fabric always feels cool. A glass of water left in a warm room feels cool for hours after. What's the deal?"
] |
[
false
] | null |
[
"Water simply has a better capacity than air to absorb heat from your fingers. Water has a much higher ",
"thermal conductivity",
" than air. Air will suck ",
" heat from your hands considering the difference between room temperature and body temperature. Water will absorb ",
" heat with the same temperature difference, simply because it can store much more of that heat."
] |
[
"On top of its greater heat capacity, as unonimus said, evaporative cooling also leaves water cooler than room temperature. This is much more of an effect if the water is in a thin layer (i.e. wet fabric), because it has a much greater surface to volume ratio."
] |
[
"There's two different phenomena at work here. The first is thermal conductivity and thermal storage capacity. The second involves phase change and heat transfer.",
"Wood has little capacity to either store heat nor conduct it. It is somewhat insulative. All insulators have that property, and air is one of the best insulators--especially when it's kept in small pockets to prevent convection. Glass has a high heat storage capacity but low heat conductivity--which is why a glass artist is able to heat a rod of glass to the melting point to sculpt all sorts of things while just a few inches away the same piece of glass stays cool enough to hold in your hand safely (albeit with gloves). Stone, water, and many metals all have both a high heat storage capacity and high heat conductivity, which is why, when you set a block of stone and a block of wood side by side in strong sunlight for a few hours, the wood will still be comfortable to the touch while the stone will feel painfully hot.",
"The other phenomena is phase change. This has to do with the different thermal properties of a solid, liquid, gas. It takes a lot of energy to change the state of a material from a solid to a liquid, or from a liquid to a gas. Heat energy. So, when water evaporates, much of the heat energy in the liquid water is transferred to the water vapor, leaving the remaining liquid colder. ",
"You can see this at work with certain aerosol spray cans--spray long enough, and even on a hot day the can itself can cool down so much that frost--ice--will actually form on the can's surface. This is because heat is being transferred from the metal of the can to the escaping gas.",
"Many refrigerators work on this principal, also. They use a refrigerant material that changes state at a certain temperature. In its liquid state, it absorbs heat, cooling the surroundings. The absorbed heat then converts the liquid into a gas, which flows to a radiator where it gives off heat, warming the surroundings there, which cools the gas converting it back to liquid again where it is pumped back to the area being cooled.",
"Those old-fashioned steam radiators you seen in many Victorian era houses work exactly this way. Steam rises. Water is denser than steam and falls. Steam rises into the radiator, releasing heat into the room, warming the room and cooling the steam until it becomes condensed water, which is dense and heavy, so it falls back down the pipe down into the boiler in the basement where it is heated back up into steam again."
] |
[
"Do computers access familiar memory addresses faster the second time around?"
] |
[
false
] |
It appears when I open a file a second time around, it opens faster. Why is this? Or is it my imagination?
|
[
"Computers usually cache oft-used data in a portion of memory that's much faster to read than your mass storage device - but the memory itself is not the same type. Most operating system will cache things like opened files in RAM and will keep them there until the memory is needed by other things. Therefore, the first time you open the file the computer is reading it off the (slow) hard disk, recording it in (fast) RAM, and displaying it; the second time it only needs to fish it back out from the RAM. Unless something's taken its place - in which case, back to the hard disk it goes.",
"This gets a bit murkier if the hard disk is replaced by a solid-state drive, which is ",
" faster for this sort of operation. The system will still cache to RAM, but the difference will be a lot less noticeable."
] |
[
"From your point of view - yes... but the third time is a crap shoot.",
"For files especially there's a lot of places that a computer will tuck data about that file that are much higher speed than actually reading it from the disk. Even the disk itself has some RAM on it that's a few orders of magnitude faster than the spinning platters for holding on to whatever it just read (or is about to write). ",
"This actually holds for other parts of the computer too - like fetching data from RAM for the CPU to process on. ",
"The whole concept is called cache. IronMew explained it pretty well so I'll leave off here."
] |
[
"/u/IronMew",
" partially explained caching, but didn't take it to its most effective level. ",
"A computer typically contains several levels of cache memory. The lowest levels are inside of the microprocessor itself. Once data/instructions have been fetched from RAM, it will store a copy on the chip itself. It uses fairly sophisticated algorithms to try to identify and keep memory that will be accessed often. When it is successful, there's a huge performance boost, since it takes roughly 1000x as long to get information from off-chip than it does from internal cache memory. This is such a benefit that about 1/2 of a modern microprocessor is internal cache memory. ",
"When the processor needs instructions/data, it will first look in its internal caches to see if it is there. If not, that's a \"cache miss\" and it is forced to go off-chip to get it. ",
"There's also an overhead associated with this. Since it is possible for data (and even instructions) to be changed by the program being executed, the processor must keep track of whether or not the copy it has is certain to be the right one....whether the cache locations are \"dirty\" or \"clean\". This process of maintaining \"cache coherency\" is very complicated, since there are various levels of cache memory. But it is worth the complexity required to do it. One of the big performance limiters for a processor is the ability to quickly get/send information to and from the outside world...the \"Input/Output bottleneck\". If a processor has to wait for information it needs to proceed, it \"stalls\" until it arrives. "
] |
[
"To increase power, why do gasoline engines add to the number of cylinders while diesel engines add to the size of the cylinders/engine block?"
] |
[
false
] |
What would happen if you modeled a diesel engine like a V12 sports car engine? Conversely, if you modeled a gasoline engine like a large Detroit diesel engine?
|
[
"Diesel engines compress the fuel air until it combusts. Petrol engines compress them less and use a spark to combust them. So in a diesel engine you get more benefit from compressing more fuel/air to combustion so bigger cylinders = more power because you get longer strokes on the piston.",
"For petrol engines you don't want to compress so much. So bigger cylinders would give some more power but still only one stroke and you can't make the stroke a lot longer without compressing too much. So more cylinders gets you more power more efficiently. ",
"This is also why diesel engines have more torque - longer strokes on each piston - while petrol engines can go faster - more rapid strokes."
] |
[
"Not quite. A diesel compresses air until it gets very hot and then injects the fuel into the hot air causing it to burn. The fuel is not mixed with air ahead of time. "
] |
[
"they don't necessarily, The GMC Duramax diesel is comparable to their gasoline engines in bore to stroke ratio and displacement. Diesel engines have to be stronger because of the increased force of compression which makes them heavier than a comparable gasoline engine."
] |
[
"Has any real scientific research been done to study meditation, yoga and other mystical phenomenon?"
] |
[
false
] |
Amongst supposed spiritual and mystical phenomenon meditation and yoga seem to be fairly well accepted as having tangible benefit to the practitioner. Has there been any studies to measure or validate their effectiveness and/or to try to discover their physiological mechanisms. Obviously some elements of yogic practice have obvious physical benefit to strengthening muscles and stretching and opening up connective tissue but there are also claims of having positive effects on organ function and glandular function.
|
[
"I feel almost guilty doing this, and if I'm in error I'm very sorry, but that doesn't sound like a medical abstract to me. It reads like some of the crazier stuff from my liberal arts days. Especially the criticism of things as \"reductionist\" and the frequent use of the word paradigm.",
"Can I have a link to the study in a journal? Or at least its title and authors?"
] |
[
"There's been quite a lot of research into exactly what's happening in the brain during meditation. One example would be this study:",
"http://journals.lww.com/neuroreport/Abstract/2000/05150/Functional_brain_mapping_of_the_relaxation.41.aspx",
"There are a bunch like that. Typically they get some practitioners in an fMRI machine and see some sort of change. This one claims a significant increase in activity in the areas of the brain regarding attention, and controlling the automatic nervous system. ",
"I can't think of any studies I've seen regarding organ/glandular function, unless you count the heart. Exercise helping cardiovascular function seems like kind of a given doesn't it? "
] |
[
"A study from earlier this year on the impact of an 8 weeks training course in Mindfulness Based Stress Reduction (a secular meditation technique) on the brain.",
"Impact of Mindfulness-Based Stress Reduction training on intrinsic brain connectivity.",
"findings suggest that 8 weeks of mindfulness meditation training alters intrinsic functional connectivity in ways that may reflect a more consistent attentional focus, enhanced sensory processing, and reflective awareness of sensory experience."
] |
[
"Do germs end up in the air after they have settled?"
] |
[
false
] |
Not sure if I posed the question correctly, but, I'm basically wondering how germs work, particularly COVID at this time. Suppose there was a warehouse of boxes just completely contaminated with COVID and they transferred it to a second warehouse, which previously had no COVID whatsoever. What would be the risk of someone getting the virus by walking around the second warehouse if he/she does not touch anything at all?
|
[
"Not highly likely, due to adhesive forces that would bind the virus to surfaces. One way that this could happen is the virus settles and adheres to some loose particulates (e.g., dust), which can be kicked up into the air, and carry the virus as a vector."
] |
[
"In theory yes,but viruses also DIE fairly quickly if they dry out, so it's very difficult to reconcile those factors. It probably COUlD BE DONE intentionally, but it hasnt been seen with Covid"
] |
[
"Covid is not a germ, it is a virus. Corona viruses only propagate through fairly large water droplets, and briefly in surfaces. They have never been seen to pass through the air in atomized air (some viruses do). Hence the 2m social distancing argument, since a cough or sneeze falls to the ground in less than that distance. Therefore, it takes direct physical contact between a contaminated surface and your face. In theory, IF someone sneezed onto the ground and you then touched that ground, you would contaminate your hand. You could even do it by walking over a spot where someone peed or vomited, and then touching your shoes. They are now warning us not to wear outside shoes indoors. But the virus is not going to jump up off the ground and chase you down."
] |
[
"Why does fire behave this way in zero gravity?"
] |
[
false
] | null |
[
"The flame is actually hot gas undergoing convection. Convection depends on the ",
"Rayleigh Number",
" which depends on gravity. Zero gravity means 0 Ra Number, which means no convection, giving a spherical flame."
] |
[
"I can't do any better than ",
"Wikipedia",
"."
] |
[
"I was confused until I realised you weren't talking about the Reynold's number... there are too many numbers..."
] |
[
"If a car acts as a faraday cage, why can I get radio signals through the antenna?"
] |
[
false
] |
And why does lightning not propagate through the antenna?
|
[
"Well, ideally, the antenna will be on the outside of the car. Then the signal will be carried inside the 'Faraday cage' of the car by wires. (Modern cars tend to have very compact antennas instead of the long whip antennas of yore, but they're typically either on the top of the car, front windshield or incorporated into the rear window defroster.)",
"It's important to note, though, that a Faraday cage is only effective for a range of frequencies of EM waves. For example, your windows are big holes in the cage, so wavelengths smaller than about a meter have no trouble getting inside. (Your GPS and cell phone antennas still work inside your car---wavelengths around 20 cm.)",
"Lightning is much lower-frequency (it's basically DC current, not even radiation) so it just wants to find a path to the ground. If the antenna is the best way to get there, it'll certainly use it, but more likely it will distribute its current over the whole car frame before jumping to the ground from the undercarriage. (This is my best guess---not an expert in lightning propagation through cars.)"
] |
[
"I'm pretty sure yoh are picturing EM waves wrong. Amplitude is not a height like it is with say water waves, it has no spacial measurement or size. We merely visualize the amplitude of a EM wave in a diagram as a height, the axis is not distance though but rather field strength. Same as if you plotted say temperature on paper, higher doesn't mean the temperature was longer. It doesn't matter what amplitude the EM wave is, it doesn't effect it's size so it doesn't make a difference for how it behaves in this way. On the other hand, wavelength is an actual spacial size measurement of a EM wave. "
] |
[
"I'm pretty sure yoh are picturing EM waves wrong. Amplitude is not a height like it is with say water waves, it has no spacial measurement or size. We merely visualize the amplitude of a EM wave in a diagram as a height, the axis is not distance though but rather field strength. Same as if you plotted say temperature on paper, higher doesn't mean the temperature was longer. It doesn't matter what amplitude the EM wave is, it doesn't effect it's size so it doesn't make a difference for how it behaves in this way. On the other hand, wavelength is an actual spacial size measurement of a EM wave. "
] |
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