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[
"I would like a very basic summary of the Quantum Field theory."
] |
[
false
] |
Hello Reddit. I am sophomore in high school. I was in my Chemistry period and we were discussing the emission of photons from electrons when enough energy is given. My instructor mentioned the Quantum Field, but VERY briefly. The idea of the theory really intruiged me, but my instructor held off from talking about it due to the number of people in my class that could be offended (religious affiliation and whatnot). So Reddit, could you give me very simple (if possible) summary/understanding of the Quantum Field theory? Thanks!
|
[
"I wrote up a description a while back ",
"here",
"."
] |
[
"Let me give it a go.",
"Imagine you have a guitar. Each string you can pluck makes a certain note. When struck together, you get a cord. When you're not strumming the strings, they themselves have properties. The properties that allow the note to emerge when it strums are fairly complicated to envision directly, so lets step back. Lets look at the density of each guitar string instead.",
"Now in QFT it isn't truly density, but in a roundabout way it is. Because if you think of frequency, it's a wave that oscillates with a high and low at a rate. When you talk about getting these outcomes for energy, you're essentially talking about whether or not something is playing one note or the other, or a chord.",
"If you want to get a bit more advanced, though still abstract, lets go on to how waves interact with matter. In order for a 'free wave' like a photon to interact with a 'chord' like an oxygen atom, it has to collapse. When the wave hits the 'surface' of the atom, it's actually hitting the first peak of the wave created by the chord that is the oxygen atom. If you want to visualize it, think of what the ocean looks like and imagine dropping something into it. The first part it hits is going to be the little ridge of water closest to it.",
"Now when that photon hits the oxygen atom, it's kind of like of like a new note playing over a chord. No matter what happens the two will briefly make a new chord, whether or not it's in harmony. If it is in harmony, then you get that effect where the chord being played suddenly sounds just a little louder. The amplitude of the frequency goes up and it just sort of flows. So to put that in QFT terms, things are in agreement, they'll resonate and a note to a chord can grow briefly into something more. If not, they'll repulse each other and create a moment of discord.",
"Now of course, the actual depth of this is absurdly more complicated than what I've conveyed. This is more of an exercise for visualizing what's taking place in a macroscopic sense. Still, it all boils down to these sort of oscillating waves of energy acting like either agree with each other in certain configurations or don't. And what happens when they do, or don't."
] |
[
"QFT is a pretty advanced topic, not usually taught until graduate school (masters/PhD level). It combines quantum mechanics (which tell us, for example, how electrons are arranged around an atom) with special relativity (which tells us how things behave when they're going really fast relative to each other), so together these things tell you, for example, what happens when two electrons approach each other at high speed. The mathematics are generally described in terms of Lagrangian mechanics and tensor calculus, but are visualized in terms of ",
"Feynman diagrams",
". You might want to check out the articles on Matt Strassler's website: ",
"http://profmattstrassler.com/"
] |
[
"Please, if somebody knows about the physics of black holes, can you explain a bit regarding their mass? (Resubmitted)"
] |
[
false
] |
I recently watched some documentary on Youtube about black holes. In the film, Kip Thorne stated that the notion that a black hole is a super-dense sphere of condensed matter is wrong, and that any matter that falls into the black hole is destroyed, and ceases to exist. If this is the case, how is it that the more matter that enters a black hole, the more the mass of the black hole increases and in-fact, black holes come in many different masses, from the mass of a small town, to many billions of solar masses. Why aren't all black holes the same? Please keep in mind I know almost nothing about the physics of black holes, and may have stated some of the question incorrectly, or noob-like. I do however understand that matter/energy (information?) is always conserved, so I guess I am really questioning exactly what he meant. Thanks!
|
[
"Some qualities are expected to be conserved, such as momentum and charge"
] |
[
"There's no telling, but another thing we know of where all matter is obliterated is the beginning of the universe, so some people think there might be a universe inside a black hole, and conversely, that our ",
"own universe might be inside a black hole",
"."
] |
[
"Matter falling into a black hole is not destroyed, nor does it cease to exist. No one actually knows what happens to matter besides that, however, it may be that when people say matter is \"destroyed\", they really mean it is ",
". The quality that makes it massive remains, but any other qualities it had outside the black hole are obliterated. Maybe. I mean, how would we know?"
] |
[
"How is it that Jupiter can keep earth safe when they orbit the sun differently?"
] |
[
false
] | null |
[
"In addition it's worth noting: ",
"1) Jupiter can attract and \"suck\" in an inbound comet or asteroid as you mentioned. ",
"2) But more often, Jupiter simply deflects and bends the orbit of asteroids and comets so that they are flung out of the solar system entirely. ",
"3) Finally, Jupiter can also bend/fling a comet's orbit directly at us on a collision course! ",
"So it's not a perfect guardian! ",
"However, the number of possible directions and angles that Jupiter can sling an object safely away from us, vastly outnumbers the narrow band of trajectories that leads to a direct impact with Earth. ",
"So... for now... it seems like Jupiter does far more good than harm, on average, in protecting the Earth. ",
"(I think astrophysicists are still debating this issue somewhat, as to whether or not Jupiter does more harm, or more good.)"
] |
[
"You can imagine the gravity of the sun being like a cone with the sun at the pointy end. All the planets are spinning along the inside of that cone at different heights.",
"Something small that would keep falling down while spinning in circles towards the sun will usually eventually get near to Jupiter and get sucked in to it before it gets to us"
] |
[
"I think I remember some discussion that early in the solar system Jupiter contributed to the bombardment of Earth. While clearing parts of the solar system it threw all sorts of things into the inner solar system, but since there are less objects now it deflects more away? I'll try to find a citation of what I saw if I can find it"
] |
[
"What causes stars to switch from Hydrogen fusion to using heavier elements?"
] |
[
false
] |
When talking about the life cycle of stars, people often say something along the lines of “when a star runs out of hydrogen to fuse into helium, it has to start performing fusion with heavier elements to keep producing energy.” But this glides over a lot of details and also frames the star as having some sort of agency, which is obviously not the case. So my questions are: Thanks in advance!
|
[
"In short, gravity compresses the core as fuel is exhausted, which raises the temperature, which eventually gets it hot enough to make the ash from the previous fusion burning stage to itself start fusing.",
"During the main sequence hydrogen slowly burns to helium, so helium is accumulating in the core. The star is in an equilibrium, where the thermal pressure is sufficient to drive H to He fusion (but not much He to C/O fusion) which balances gravity. But that's just a story we tell to children so they can sleep at time. ",
"Over the course of the H-burning main sequence life, you can see that the H is slowly getting exhausted. In order to keep up the rate of energy production to balance gravity, the core does have to get a bit hotter and denser because it has less H. So in reality, over the main sequence life of the star the core density and pressure are slowly increasing in order to maintain the balance- the core slowly contracts, increasing the density and pressure, and the equilibrium output moves slowly to a greater luminosity. As a result, the star finds a new balance- it gets more luminous and it grows, so its surface temperature decreases. This is very very gradual, and is not the transition to a giant phase yet. For most purposes, you can pretend that the luminosity during the main sequence part of the star's life is effectively constant. But if we're being honest, our sun is halfway through it's life and it is actually a few percent more luminous (and redder) than when it formed. ",
"If you repeat this process until the point where H fusion is not sufficient to balance the star, you'll find that the core contracts due to gravity. This drives it to greater luminosity, coincidentally, causing the star to slowly grow in a giant phase. Most importantly, the contraction causes the core to reach higher temperatures, and this is the key to getting your next stage of fusion burning. Due to the greater Coulomb repulsion between larger nuclei, they need greater kinetic energies (and thus temperatures) in order to burn efficiently. It is ultimately the core contraction (inside a growing star!) which heats the core enough to 'unlock' the next stage in nuclear burning. ",
"If you want to know more, the 'helium flash' is a really interesting feature of low mass stars as they make the transition to a giant phase and helium burning."
] |
[
"Fine explanation by ",
"u/VeryLittle",
". ",
"I'd just like to add that the equilibrium he mentions, is a balance thing between outward pressure and inward pressure from gravity. ",
"Outward pressure comes from the energy released by fusion of hydrogen and then increasingly heavier elements.",
"As the lighter elements are spent, the relative density near the core increase, resulting in higher pressure, enabling fusion of heavier elements. If a star has enough mass to have a high core density to start with, it will produce small amounts of heavier elements while burning through it's hydrogen, but the outward pressure from the fusion of hydrogen is sufficient to limit the core pressure enough, that hydrogen is the predominant fuel.",
"Stars with little mass like red dwarfs doesn't have the amount of stuff required to build internal pressures to such a degree, that fusion of helium is possible, so they indeed just \"die\"",
"Really massive stars can produce energy by fusing elements all the way up to iron."
] |
[
"Switching maybe isn't the best expression, after hydrogen burning doesn't stop. It just moves to outer regions, where there is more hydrogen left.\nSo there only is an additional process, when the needed temperature is reached."
] |
[
"Is there a way of calculating how much energy is released when speaking?"
] |
[
false
] |
[deleted]
|
[
"Are you more interested in the energy embodied in the actual sound produced, or the energy your body uses in producing it? The first one is easier to answer."
] |
[
"You can convert the dB level back to sound intensity. That, if you know how far the dB level is from your mouth, you can roughly know the original required power. Then you have to factor in losses in several assumptions you make."
] |
[
"There are a couple useful equations here.",
"First is how we calculate sound intensity:",
"L (in dB) = 10 x log (I/I0), where I0 is the \"standard reference sound intensity\" of 10",
" W/m",
" . ",
"The second is what relates intensity to power:",
"I = Power/Area ",
"If we assume a spherical distribution of sound from the source, then we have",
"I = Power/4xpixr",
"If we assume you speak at 70 dB, this corresponds with an intensity of 10",
" W/m",
" . If this corresponds with a speaking distance of about 1 m, this would be a power of about 10",
" W. If you speak for one second, that would be 10",
" J. "
] |
[
"Is there a reason why radio towers aren't used for wifi?"
] |
[
false
] |
The title says it all really. Is there a physical reason why radio towers aren't used for wifi. It seems to me that something like Google fiber, where they are trying to provide high speed Internet to people at a low cost could be mitigated by providing high power radio waves. I know about the inverse square law, but something like having the main depo the same as the exchange point (which can provide much more than 1gbps, probably closer to 1tbps in total) would be able to blast out a decent wifi signal with Google instead handing out cheap repeaters. It gets rid of the cost of wiring up to individual houses, speed boosts are all there still and the range is arguably better, since no longer do you need to be in your house to get signal. Anywhere in your town is fair game.
|
[
"wifi is in what is commonly referred to as the \"junk band\" - reserved for consumer use. The FCC limits how far the signals can propagate for that spectrum. and the reason for that is there is a limited amount of it. You don't want signals interfering with one another. You know how if you close neighbor is using band 2 for his wifi, you have to pick another band for your own? (perhaps you don't - just occurred to me most modern wifi access point have an auto band select mode) If someone put up wifi on a tower, no one in the area would be able to have their own wifi on whatever band was being used."
] |
[
"Radio towers (specifically, cell towers) are certainly used for ",
". It's just called GPRS or HSDPA or 3G or 4G or what have you. \"Wi-fi\" (that is, IEEE 802.11 wireless LAN) is optimized for local area usage and would not be a good choice for long-distance data transfer. Of course, as the number of users per tower, and the distance to the tower, are both much higher than with Wi-fi, you can't except the same sort of speeds."
] |
[
"To add, the radio signal is very low bandwidth when it travels. Best analogy I've heard. ",
"Stand on top of a mountain and shout down with a megaphone to a crowd below. They can hear you perfect right? Now imagine all them shouting back at you, hard to hear right?",
"It is easy to send out signals to places (hence why download is always faster than upload) but harder to \"push\" the signal from you to the radio tower"
] |
[
"Are all the particles of the same kind in the universe, say protons, identical? If not, what makes them unique?"
] |
[
false
] | null |
[
"There is no evidence to support otherwise",
"In fact, there is ",
" of evidence to support the fact that they ",
" identical."
] |
[
"It's not just that we haven't noticed a difference. Quantum waveforms don't add like regular probabilities. If you get the same state two different ways, they'll interfere. If you have two different states, they won't. Two \"different\" protons will interfere with each other, so we know they must be identical."
] |
[
"Yes, they are fundamentally identical."
] |
[
"What would a highly curved universe look like to an inside observer?"
] |
[
false
] |
This might be more of a mathematics question than a physics question. Under the FLRW model there are two possibilities for a non-flat universe: positive curvature (3-sphere) or negative curvature (hyperbolic space). Let's assume a fixed static metric for simplicity, that the universe has existed forever, and that the curvature is high enough to be noticeable. Reasoning by analogy with the two dimensional case, I'd expect far away objects in the sphere to look bigger than in flat space, eventually covering all your field of vision when the object is at the antipode. Also, I think you would see an (inverted?) image of your back in the background at all times. In contrast, objects in the hyperbolic space would look much smaller than in flat space the further they are, since parallel lightrays eventually diverge. Is this correct? Or are there other effects due to the finiteness of the speed of light? Does anything interesting happen if the observer is moving at relativistic speeds, and/or if we include a slight metric expansion? I'm basically trying to get a feel for the global aspects of the geometry from the perspective of someone inside.
|
[
"The program ",
"Curved Spaces",
" shows this well for both positive and negative curvature. Your second paragraph is correct."
] |
[
"All of what you guessed for the 3-sphere and hyperbolic space is correct. ",
"The other questions are a bit too much for my puny brain to work out. You might be interested in googling 'angular diameter distance' and reading as much as you can about it, and see if there's any good treatment for a spatially curved FLRW expanding Universe."
] |
[
"That's deceivingly simple, t must be the retarded time, that is the time at which the light from the object has to have been emitted for you to get it now. Computing this involves an integral over time including the behaviour of the scale factor at all intermediate times."
] |
[
"You hold Vitamin B12 under your tongue to absorb faster. Would the same apply to alcohol or caffeine?"
] |
[
false
] |
[deleted]
|
[
"It works for a lot os substances. What happens is the by putting something under your tongue that substance eventually gets absorbed directly in the bloodstream, while if it is ingested, it first goes to the stomach and intestines, then to the liver, and only then to the main blood supply, after suffering some transformation/filtering by the liver.",
"The same \"shortcut\" can happen in other mucous tissue of the body, like rectum, nose and lungs, so thats why we have several formulations that can use these tissues to be delivered. "
] |
[
"Works for nitroglycerine very well."
] |
[
"Sublingual absorbtion definitely works well for caffeine. I don't know about alcohol, but I know holding it under your tongue wouldn't be pleasant!"
] |
[
"How are we affected by the speed of our travel through the universe?"
] |
[
false
] |
Let me be more specific. If we're travelling at insane speeds through the universe (due to the earth's spin, the rotation of the solar system and the speed of the solar system around the galaxy and then the galaxy's motion through the universe) then how do we accurately measure the speed of light due to the fact that the tools to measure it are also moving through space but the speed of light is constant and therefore what we perceive to be the speed of light might be faster or slower depending on our velocity through space. Also, how are we affected by the time dilation of this motion and could we therefore be experiencing our universe slower or faster than other objects in the universe? Thanks guys
|
[
"speed of light is constant and therefore what we perceive to be the speed of light might be faster or slower depending on our velocity through space",
"Nope. The speed of light is constant ",
". (Inertial means no rotation or acceleration) It is what is known as a Lorentz-invariant quantity.",
"Two observers moving at a constant 0.999",
" relative to one another will both measure light to travel at ",
".",
"There is no such thing as absolute velocity. All inertial frames can equally claim to be stationary. Therefore all velocities have to be quoted with respect to something else (e.g. the Earth), otherwise they're meaningless.",
"This is an axiom of special relativity, and is essentially where all the weird effects like time dilation and length contraction come from."
] |
[
"If we're travelling at insane speeds through the universe",
"Compared to what?",
"Also, how are we affected by the time dilation of this motion and could we therefore be experiencing our universe slower or faster than other objects in the universe? Thanks guys",
"Time dilation is only defined with respect to another frame. So from our point of view, anything that's moving with respect to us will have their clocks running slow compared to our clocks.",
"Since there is no absolute measure of time in the universe, there is no absolute measure of time dilation."
] |
[
"Compared to what?",
"There was an article on IFLS where they showed how fast we are moving in total relative to our nearest galaxy which the milky way is heading towards. It's a couple of million mph.",
"As for time dilation it looks like I'll have to try understand a bit more about relativity before being able to ask some questions on it that are more meaningful. Thanks"
] |
[
"What would a pipe organ sound like on planets with wildly different atmospheres than Earth's?"
] |
[
false
] |
I found and which both focused on the sounds of a pipe organ on Earth, Venus, Titan, and Mars. The pitch and effective propagation of the sound changed due to the atmospheric differences. I would like to find out more about this subject and predict what this same pipe organ might sound in more extreme environments such as the gas giants of our solar system or some of the exoplanets discovered by the Kepler telescope. I am a sound design student who is very interested in space and these concepts, but the physics and equations involved in the paper that I shared is not something that comes easy to me.
|
[
"Lighter gasses cause higher frequencies. heavier gasses cause lower frequencies. higher air pressures cause a higher speed of sound.",
"We have no working microphones near the surface of mars because all mics we send down broke or have been shut down early. But a few mars orbiters could hear good enough to hear large storms and anything that enters mars atmosphere.",
"Huge gas nebulas can carry low frequency sound waves, caused by nearby suns and supernovae, pretty far.",
"some audio recordings from other planets:",
"http://www.youtube.com/watch?v=36ffV-CI3Mo#t=95",
"damn i didn't find more. there is so much nonsense about this."
] |
[
"The speed of sound is\n sos=sqrt(gamma*pressure/density) ",
"Gamma is cp/cv which depends which gasses you have in your medium. You can probably look up all three or just Google speed of sound Jupiter. You can calculate this and then find your change of pitch accordingly! "
] |
[
"Yes I noticed the correlation and read within the linked paper what caused the pitch change. My question is what would the pipe organ sound like elsewhere; how would I calculate that? I can find atmosphere variables for other bodies but I literally don't understand the equations :/",
"Edit: there is a lot of nonsense out there. I spent a few hours wading through information that didn't have explanations behind how the sounds were created. It's amazing how little information there is with documented processes. I wonder if a sound designer can have a career in space research."
] |
[
"What's the highest frequency laser?"
] |
[
false
] |
I've been playing the game Stellaris which has a late-game technology you can research, gamma-ray lasers, which got me thinking about laser frequencies. The certainly makes them sound like a difficult research project, not something in production. The graphic they have seems to imply the highest-freq commercially available laser is pretty solidly ultraviolet. Are there higher-freq research laser, and if so, what are they used for? Is the trouble in producing higher frequencies finding an appropriate gain medium? If so, what research is there in finding such materials? If not, what IS the main obstacle? Further questions: if we had such a laser (gaser?) what would be some of the research, industrial, commercial, and military applications that we couldn't do with a UV laser? In particular, would this have applications in laser fusion? Also, searching this subreddit, I found , which doesn't sound that hard in the thread. Could this method, or some other method of raising a lasers frequency, other than the brute force approach of just accelerating the emitting device relative to the target, be used in production of a high-freq laser? How does this apply to the above?
|
[
"It depends what you mean by a laser. If it actually has to work through a lasing mechanism (involving population inversion and whatnot), the current limits are in the ultraviolet. I read a paper a few years ago claiming to get 10 nm radiation...I don't know if that's a record or what.",
"Above that there are free-electron \"lasers\" which don't operate under the same mechanism (they involve wiggling fast electrons with magnets) but still produce coherent radiation, including x-rays. These are used in synchrotron facilities. Gammas rays are the same thing as x-rays except they come from nuclear or particle interactions instead of electronic. Gamma ray sources for radiology are basically just big shielded wads of an unstable isotope with a window in the shielding that can be opened. ",
"In principle nuclear isomers could be used to make a gamma laser...but I don't think that technology is at all close to existing. Now I see that that's what that Wikipedia page is about, but most of the references are from the 80s or earlier. Probably the development of free-electron lasers made that less of a goal. ",
"Here",
" is a proposal to make one out of positronium, where the gamma rays would be produced by electron-positron annihilation. ",
"Here",
" is one talking about exciting nuclear isomers into gamma ray lasing. Both of these rely on Bose-Einstein condensation to make the radiation coherent. Nobody has actually done this, but the second one at least seems possibleish."
] |
[
"You're right that there are X-ray Free Electrons Lasers, although current only two are operational (LCLS, in Stanford CA and SACLA in Japan). They aren't quite the same as synchrotrons; the electron energy produced by those isn't high enough to produce coherent light, as it needs to propagate through the undulator - the spatially oscillating magnetic field - for long enough that the electrons are sorted into bunches by the radiation that they are producing. This generally needs a much longer chain of magnets than the 'wigglers' used to generate synchrotron X-rays. Therefore, XFELs need a long linear accelerator instead - in Stanford, they used the last km of the old linear accelerator.",
"As you note, it's not really a laser as there's no lasing medium etc. but the light produced has many, or even all, of the same properties. The beam size depends on the electron bunch and undulator, I think, but they can be focused down to similarly small spots as lasers - record in Japan is spot sizes of a few nm using Kirkpatrick-Baez mirrors, whereas in LCLS they use beryllium compound refractive lenses (which are pretty cool because the 'lens' bit is actually a hole in the beryllium solid) which I think only get down to spot sizes on the order of microns."
] |
[
"The DESY XFEL is online now too and going into user operations this year, I believe, and the FERMI soft-XFEL at Trieste has been up for a while. Also the XFEL at PSI is now working although not in user-use yet. "
] |
[
"Does the moon have a mantle?"
] |
[
false
] |
If it doesn't why does the earth? Do all planets have a molten core? If they don't what are the circumstances for having one?
|
[
"The moon does have a mantle and a small liquid outer core. ",
"All terrestrial planets have a molten core and mantle to some degree , as do the larger moons. ",
"The mantle and the core are hot due to radioactive decay as well as some residual heat from the formation of the planet. The moons of Jupiter are also heated internally by the strong gravity of the gas giant. Larger terrestrial bodies generally have more radioactive material and a higher initial temperature so they have larger amounts of molten rock under the crust"
] |
[
"If by similar you mean made by the same element ratio, then yes more or less. Otherwise no. It is nowhere near the same relative size nor does it produce a geodynamo magnetic field. ",
"The magnetic field on the moon is very weak and is either due to the remnants of geomagnetism or from large impact events. "
] |
[
"Follow-up, then: Does our Moon have a magnetic field? I assume its core is similar to ours, am I correct?"
] |
[
"Nocturnal Dinosaurs, evidence and how common?"
] |
[
false
] |
We have predators today that are nocturnal. We have raptors (more closely related to dinosaurs than reptiles). It seems almost certain there would have been nocturnal dinosaurs. Are there any studies or evidence of there being nocturnal dinosaurs yet or are we left to speculation and assumption? How common would it have been? What in the fossil record indicates whether a creature was nocturnal or not?
|
[
"Not many publications, and inference based on indirect measurement.",
"For example Michael Menaker applies principles of chronobiology to mammalian fossils in the following paper (using phylogenetic inference to determine the potential biology of extinct species relative to the overall groups they belong to, lead up to, or span).",
"http://rspb.royalsocietypublishing.org/content/280/1765/20130508",
"Schmitz and Motani report in the journal Science a different approach applied to dinosaurs, whereby they infer the function of the dinosaur eye based on the size of the scleral ring (the assumption being that the pupil size is more or less strongly related... and thus nocturnal (big pupils associated ring size), diurnal small (concordant change).",
"http://science.sciencemag.org/content/sci/early/2011/04/13/science.1200043.full.pdf?explicitversion=true",
"They also report a combined approach (phylogenetics and form/function) here, but no real strong inference about how dinosaurs went about their business. More a technical description of how you could strongly support the kind of science you are interested in.",
"http://onlinelibrary.wiley.com/enhanced/doi/10.1111/j.1558-5646.2011.01271.x/"
] |
[
"No problemo. If I spot any other publications (got me interested in it frankly) I'll report here."
] |
[
"Thank you."
] |
[
"Are Bill Nye and Neil deGrasse Tyson wrong on DeflateGate? Wouldn't a ball cooled from 80F to 50F be 2 psi under 13 psi?"
] |
[
false
] |
If a football had a (gauge) pressure of 12.5 psi inside at 80F and brought outside to cool to 50F what would its pressure be? I am asking because two science populists have publicly gotten this straightforward calculation wrong. has publicly stated a football to deflate 15% (note the accusation is 2 psi which is about 15% of the gauge pressure) it would need to cool from 125F to 50F. has said "Rubbing the football, I don't think you can change the pressure. To really change the pressure, what you really need to change the pressure is one of these – the inflation needle" . (Despite that rubbing the football can by friction warm the football, which by the ideal gas law would increase the pressure). EDIT: I should add that other people accept the physics argument from the Patriots correct. lists: Of interest, one of the professors in this article made the common mistake of forgetting to account for atmospheric pressure and calculated a ball cooling from 80F to 53 F would change from 12.5 psi to 11.9 psi (which is what you'd get if you didn't factor in atmospheric pressure. The mistaken calculation: 12.5 psi (53+459.67)/(80+459.67) ~ 11.9 psi. As for the Boston-area professors, could they be influenced by their football allegiances? They all said no. Naughton is a lifelong Buffalo Bills fan, but said, “My answers to any of these questions don’t change regardless of whether I’m a fan or not.” : Neil deGrasse Tyson and states a ball cooling from 90F to 50F would account for a 2 psi loss in pressure.
|
[
"I don't think you can assume constant volume here. The ball is elastic and the relationship between pressure and volume is almost certainly non-linear."
] |
[
"I think the assumptions that the starting temperature of the ball was 80F and the end temperature of the ball was 50F can be challenged. ",
"Dropping from 85 F to 45 F would take a 12.5 PSIg football to 10.5 PSIg \n. That doesn't seem outside the realm of possibility. "
] |
[
"This Youtube experiment",
" conducted by HeadSmart Labs shows that a football inflated to 12.5 PSI at 75 degrees loses 1.80-1.95 PSI at 50 degrees when damp, simulating conditions at Gillette Stadium last Sunday.",
"The coach of the Patriots says that a \"rubbing\" process performed on the balls shortly before they were presented for inspected temporarily increased their pressure by 1 PSI due to frictional heat. To give everyone an idea of what this \"rubbing\" might look like, ",
"here's a video",
" of 7 ball boys from the Green Bay Packers power-scrubbing their balls just before inspection.",
"Also, ",
"a new report yesterday",
" claims that the balls were measured at halftime at \"closer to one pound below 12.5 PSI.\" I interpret this to mean the balls came in at 11.0-11.5 rather than 10.5 PSI."
] |
[
"Is there a limit to how loud a sound can be?"
] |
[
false
] |
For example, if I'm in a sealed room, is there a limit to how loud something could be in that room? Is there a different limit for different mediums?
|
[
"Sound waves are compression waves that propagate as deviations in the pressure of a medium. The amplitude of a sound wave is related to how much of a deviation in pressure there is in the sound wave relative to the \"reference\" pressure (the pressure inside the room when it is \"silent\"). Therefore, the loudness of the sound is limited by how much of a change in pressure it can cause to the air in the room.",
"If your room is filled with air at sea level, we can assume that the reference pressure is atmospheric pressure (101.3 kPa). Therefore, a simple theoretical limit on the amplitude of a pressure wave without it becoming distorted at the lower end is 101.3 kPa, because it can't go lower than 0 pressure. ",
"This corresponds to about 194 dB",
" as a maximum volume. ",
"This website",
" puts that into perspective. A shotgun blast is about 165 dB and the tissue in your ears die after 180 dB.",
"This limit will change for different mediums and different pressures. For example, it would be lower at a higher elevation, where there is less atmospheric pressure. If you go to space (which we can treat as a vacuum), the limit effectively becomes zero as there is very little pressure. "
] |
[
"Just a reminder for OP, db is a log scale. So the 15 db difference between a shot gun and \"ear-death\" is a whole lot ",
" than the 14db difference of the theoretical max."
] |
[
"So above ear death we get to \"blow your skin off\" sound levels?"
] |
[
"What is actually going on with new COVID-19 variants and their mortality rate?"
] |
[
false
] |
There seems to be a new variant each week, which are being labelled as 'variants of concern'. I understand that they're usually related to the vaccination efforts and ensuring people will be protected against new variants, long enough for the vaccines to be tweaked when an inevitable, vaccine-resistant strain emerges. I'm not worried about that, because each of these new variants don't seem to fully bypass any of the vaccines yet. What I am worried about is some variants being reported as more lethal, for example the UK and California ones. I understand the news will use sensational headlines to catch people's attention, but shouldn't a virus start mutating to be dangerous? And if this isn't the case for coronavirus, will there be a peak mortality rate or will it continue to climb?
|
[
"The more people get infected, the more variants we will see appearing. It’s not the same having a 0,001% probability in a hundred cases than in a few millions. Generally, being less deadly and less noticeable means that one infected person will be able to spread the virus more before feeling sick and retreating from their social environment. But in this case, coronavirus already has a long incubation period where most of the infections happen. And if one, or anyone around them, shows any symptoms, they will likely be put into quarantine or hospitalized. So I think (and this is my opinion) that the variants that become dominant will be those that have a bigger chance to spread on those two weeks, regardless of what happens to the host after that point."
] |
[
"\"No evidence [yet] that vaccines reduce community spread\" is much different from \"evidence that vaccines don't reduce community spread\".",
"This is a difficult thing to study in a controlled way, and unethical given the ongoing pandemic, but ",
"observational data strongly suggest that vaccination with the Astra-Zeneca vaccine substantially reduces transmission",
" (pg. 18) and ",
"Israeli data on the Pfizer vaccine is strongly suggestive of the same thing",
".",
"The same mechanisms that allow a vaccine to provide protection to an immunized person will ",
" tend to reduce contagiousness, as transmission is a numbers game and fewer virus particles (a product of the vaccine) ",
"means fewer transmission opportunities",
"."
] |
[
"That's what viruses do. They tend to mutate frequently. It's random process. Some mutations make them more infectious and such viruses become more prevalent logically. Some mutations can make them more deadly (not that viruses have intentions) and some don't change much. Logically mutations that promote spreading are getting dominant over time."
] |
[
"Considering that a mirror changes the direction of photons, is it actually \"deformed\" or even \"used up\" in the process?"
] |
[
false
] | null |
[
"Yes, it's accurate to say that a mirror will be subjected to a ",
"deformation",
" when a beam of light is applied. The reason is that photons have a finite momentum, and because the mirror changes the direction of travel (and hence the momentum) of the photons in the original beam, it itself must experience a change of momentum (due to the ",
"conservation of momentum",
"). By ",
"Newton's second law",
", we can express this change in momentum as a function of time as a force: F = dp/dt. This so-called radiative force in turn will in turn produce a ",
"pressure",
" on the area of the mirror that it impinges on. As an aside, this is the exact scheme that could be used to power spacecraft in space using the light of celestial bodies via ",
"solar sails",
".",
"In other words, the mirror will be slightly bent in the region over which the beam hits it because of the resulting radiation pressure. However, since this pressure is relatively low (because the momentum carried by photons is relatively small), the mirror will usually not be permanently altered by the beam and will return to its equilibrium position once the beam is removed (this is called an ",
"elastic deformation",
" in the language of engineering)."
] |
[
"When photons lose energy, they reduce their frequency. So blue light might turn into red light. All photons go at the same speed in the same medium."
] |
[
"That shouldn't happen. It will be very slightly dimmer and there may be imperfections, but it should look very much like the real world. Remember everything is twice as far away in the mirror. Maybe you need glasses. "
] |
[
"Can you absorb nutrients through the colon?"
] |
[
false
] |
So I have heard of "butt chugging" which is you putting alcohol in your anus and absorbing the alcohol through the bloodstream to get drunk. My questions are: Thanks for all of your help in my morbid curiosity!
|
[
"The short answer is, yes! To some degree you can absorb substances through the rectum, which is why many medicines are made with suppository formulations. Some things such as alcohol and water can also be absorbed. Anything that is absorbed into your body and metabolized, regardless of the route of ingestion, could provide calories. A shot of vodka that is ingested has would have pretty much the same calories if you inhaled it, or put it up your butt! So I guess you could pick your favorite route. The danger with alcohol is that you have no protective response to getting rid of it if you've had too much... your body doesn't have a reflex to \"vomit\" out your butt. I mean you could, but I would never take you out drinking again. Some nutrients would probably not be absorbed rectally, such as fats or nutrients that require cofactors like B12, but I honestly don't know specifics about which things can and can't get absorbed.",
"On a non-academic note, I'm pretty sure that crazy british guy who always drinks his own piss put something hydrating up his butt one time, like seawater or something. If that show stays on the air long enough though, I bet that man will butt chug his own piss... which I would definitely watch... for science. "
] |
[
"I would add that the nutrients need to broken down (or digested) and need to be hydrophilic (fat would be very difficult) in order to be absorbed through the colon. A ",
"TPN",
" formula would be a good example of what state the nutrients need to be in. All fat soluble vitamins would not be absorbed (except perhaps K) as well as most water soluble nutrients due to the specific uptake mechanisms involved. In fact the only nutrient that I am reasonably sure would get absorbed is glucose (and water of course)"
] |
[
"I agree entirely. And yes, Bear Grylls is totally nutter butters."
] |
[
"can a butane lighter increase the temperature of aluminum to its heat of vaporisation?"
] |
[
false
] |
I ask because I ran into this thread I tried doing the problem my self, you know Q=(c)(m)(change in T), but I am a bit rusty in physics and some how wound up with an answer of change in T=154596198 kelvin, which is obviously not right.
|
[
"You're asking the wrong question. All you need to do is compare the temperature of the flame to the boiling point of aluminum.",
"From your links, the temp of Butane flame is like 3500C and the boiling point of Al is 2500. So YES, a butane lighter will certainly evaporate Aluminum! ",
"Fyi, the equation you posted is not the latent heat equation, because temperature does not change during a phase change. Heat of vaporization can be defined as how much energy is needed to evaporate X amount of Aluminum. The equation is Q = m*L, where Q is energy input, m is mass, and L is how much energy is needed to change the phase of 1 unit of mass."
] |
[
"I agree that temperature is the main factor, but with many issues about how realistic this is.",
"Aluminum is a pretty good conductor, so any heat you put in will rapidly spread out. So for this to work a very small piece of aluminum would help.",
"Then there is heat loss to the surrounding environment. Any cool air in the region is going to cause heat loss and lowered temperatures.",
"Then don't forget about oxidation. Any exposed Al will rapidly form Al2O3. Wiki tells me that has a mp/bp of about 2000/3000 C so maybe things aren't ruined but that is going to be important. You can't just get rid of the oxygen or your butane won't burn.",
"But going back to the original post from the OP, the whole thing sounds plausible. Al does have a rather low melting/boiling point compared to a lot of other metals (steel in particular). And the post references years of use so even small amount of Al vapor could add up."
] |
[
"ah I see, I should have paid more attention in physics, thank you"
] |
[
"A habitat is built on the moon: if we didn’t put down an artificial floor would air leak out through the ground under the enclosure?"
] |
[
false
] |
I doubt it would be fast, but would the ground act as a semi-vaccuum membrane of sorts?
|
[
"I'll disagree with ",
"u/chodpaba",
" with the caveat that I specifically only know about ",
" sciences. But so far as I know, the soils on mars and the moon are of a granular nature similar to the ones we have on earth, with little to no organic carbon components or water. On Earth there exists the ",
"vadose or unsaturated zone",
" on the land which is a region in the depth of the ground above the water table where air and gasses also exist in the void spaces of the soils. Gasses can flow through these void spaces at times, if they are produced by a chemical process or forced by a pressure difference. H",
"ere is a paper I could find",
" which discusses some of the applications as I mentioned and others.",
"So I will conjecture that if the soil or moon dust under a unsealed habitat would be granular in nature, the vacuum of space would also exist in the pore space of the soil, and so the atmosphere would leak out through the ground. The flow would be restricted by the sizes of the pore space however, and so if you were to compact it or go down to solid rock it would be feasible while the biggest challenge would be sealing the edges of the enclosure. Another note, as the size of the enclosure got bigger, it would be more efficient, as long as it was ",
"contiguous and compact",
" along the ground because the flow of a fluid from the ground in the center of the enclosure would have to travel a much further distance under the same pressure difference. I am basing this mostly on my understanding of ",
"Darcy's Law",
" wrt water in soil, anyone please correct me if I am erroneous."
] |
[
"Soil on the earth and regolith on the moon are porous. Air can travel through."
] |
[
"Thank you for the reply. ",
"I should have clarified that this was a bit of a whimsical question influenced by ",
"this post in retro futurism",
". I just imagined atmosphere leaking out of the habitats in that picture and wondered whether vacuum can extract atmosphere slowly and indirectly. "
] |
[
"Need help translating Chinese publication. side note: chinese using HIV/AIDS in research!?"
] |
[
false
] |
So a hospital in China just published an article about spinal cord injury and I need to see what concentration of LiCl they used in transplantation. I tried skimming over the original document / / and could not find what I was looking for. Then I used google translator, and it completely botched the translation (columns overlapping). If someone who can read chinese could take a look over the article and let me know what concentrations of LiCl they used in vivo, I'd greatly appreciate it. SIDE NOTE: maybe it was google botching the translation, but I kept on reading things about HIV and AIDS. WTF!?
|
[
"It looks like they did a daily injection of 85 mg/kg intraperitoneally.",
"80 只大鼠随机分为 4 组,每组 20 只: (1) 脊髓全横断对照组(A 组, n=20): 仅行T9 平面脊髓全横断, (2) 氯化锂组(B组, n=20): 脊髓全横断+氯化锂(",
"),(3) 细胞移植组: 脊髓全横断+hUCB-SCs 移植(C组, n=20),(4) 氯化锂+细胞移植组(D组, n=20): 脊髓全横断+ hUCB-SCs移植+氯化锂.",
"80 rats were divided into 4 groups, each group containing 20: (1) total spinal cord transection group, control (group A, n=20): only total spinal cord transection performed, (2) LiCl group (group B, n=20): total spinal cord transection + LiCl (",
"), (3) cell transplantation group: total spinal cord transection + hUCB-SCs transplantation (group C, n=20), (4) LiCl + cell transplant group (group D, n=20): total spinal cord transection + huCB-SCs transplant + LiCl.",
"As for the AIDS thing, it's because whenever the authors mention a measurement in microliters or micrometers, the Greek letter for mu (μ) turns into zi (滋) in the Chinese character set, which is part of the transliterated word 艾滋病, for AIDS. It's purely a fuckup from when the code for a character that doesn't exist is crammed into the corresponding value and it just happens to be a character associated with AIDS.",
"Also, part of the reason the translation was fucked up was because the European/North American encoding for the Chinese comma, the Chinese colon, and the Chinese enumeration sets (the 1, 2, 3, 4 with circles around them) translates into an actual word character that ends up adding nonsense gibberish to the final text when it's put through Google translate.",
"Now you know!"
] |
[
"I also saw HIV in there though. Then again Iraq was in there once or twice.",
"thanks for your help though!"
] |
[
"I didn't Google translate the whole thing (only a paragraph to see what you were talking about), but other Chinese grammatical characters will also give you nonsense when put through Google translate (colon, comma, period, etc)."
] |
[
"Help me restore my faith in Maxwell's equations"
] |
[
false
] |
I have trouble wrapping my head around this... One of Maxwell's equations says that the eletric flux through a closed surface is proportional to the amount of charge enclosed by it. But I can imagine a case where that is not true. Suppose you have a uniform, nonzero charge distribution everywhere in the universe. Since all directions are perfectly symmetric with no preferred direction, I guess the electric field would be zero everywhere. So an closed box would have no flux through it but would enclose a net charge. Please help me understand the flaw in this. Thanks to everyone that responded. I think I have a better understanding. No boundary conditions and an indistinguishable scenario from an empty universe. It makes a lot more sense.
|
[
"s2 is just outside",
"o.O How did you know that.... ?"
] |
[
"In brief: Integration by parts ",
" require knowledge of boundary conditions.",
"Luckily, in physics we don't need to be rigorous. We just need to be in agreement with observation."
] |
[
"I only just read your username. My comment is just, well, stupid now."
] |
[
"Are spiders immune to getting stuck in their own webs?"
] |
[
false
] |
And/or does it matter with webs from other spiders?
|
[
"Spiders are able to generate two kinds of silk",
"—one sticky, one not. The spokes of the web are made from the non-sticky silk, and spiders carefully traverse their own web. In addition, ",
"tiny hairs and oils",
" on their leg, as well as how they grasp and release their web with each step, prevent them from sticking."
] |
[
"Crazy... I’ve lived my entire life around a lot of spiders and never known this. Thanks for the great answer and link!"
] |
[
"I don’t know about other spiders, but the shaker spider (aka cellar spider) makes messy tangled 3-D webs that can definitely trap other spiders. Once they’re trapped, the shaker spiders use their long legs to wrap their victims in silk, and then it is chow time. ",
"I generally don’t like spiders, but I used to leave the shaker spiders alone and let them do their thing, as long as they stayed away from me. "
] |
[
"What determines the angle, length and curvature of a rainbow?"
] |
[
false
] |
Does is change depending on where you are in relation to clouds/water molecules?
|
[
"A rainbow is always a circle centered on the shadow of your head, the circle always has a radius of 42",
". The rainbow will be visible whenever water droplets are present in the right place and not blocked. ",
"It's always in that spot because that's where the refraction angles are correct for your particular eyes in your particular position. If you move the rainbow moves with you."
] |
[
"the circle always has a radius of 42 degrees",
"Eh? How is a radius measured in degrees? "
] |
[
"Just like the stars are charted in the sky by their angle from the horizon or other features. The center of the rainbow is a particular direction opposite the sun (a ray from your eyes to the shadow of your head basically) and the rainbow appears in any direction that makes an angle of 42",
" with that center."
] |
[
"Can an isotope have a negative number of neutrons?"
] |
[
false
] |
proton = upQuark + upQuark + downQuark neutron = downQuark + downQuark + upQuark A nucleus can be described by its number of upQuarks and downQuarks, if their positions are a blur. On the other hand, many videos show protons and neutrons as nonoverlapping balls, which I take to mean vibrations that attract and repel at various distances. Can a neutron and proton in the same nucleus swap positions?
|
[
"You cannot have a negative number of neutrons.",
"Can a neutron and proton in the same nucleus swap positions?",
"There are excitations of nuclei in which protons and neutrons vibrate back and forth, out of phase with each other. These are called isovector giant resonances."
] |
[
"No! \nEven a nucleus with protons only could hardly exist. For example 2 protons together as 2,2He can exists for very very short time and next beta+ decays. So even with 0 neutrons is not stable at all. Something is needed to compensate the repulsion of positive protons. And as I see only 2 stable combinations of 1st generation quarks exists like proton and neutron.",
"I guess you are asking are there nucleus with a different combination of quarks, in a such quark mixture that if calculated like the formulas before to give you negative neutron count. There are successful experiments with nucleus with a different kind of quarks, like hypernucleus containing hyperon. ",
"But well how to combine quarks I'm not specialist. Please check theory."
] |
[
"Neutrons are a physical, countable thing. You can't have a negative number of neutrons the same way you can't have a negative number of apples. "
] |
[
"I'm reading about mu-metals and I had this question..."
] |
[
false
] |
Let's pretend I'm holding two magnets close to each other and I'm just barely able to counter the attraction. If another person sticks a mu-metal sheet (of size >> than magnet size) in-between the magnets do I stop feeling any attraction? or is it just that the mu-metal won't feel anything and the rest will go unaffected? Whatever the answer may be, can you suggest good reading on those high "mu" materials (other than wikipedia) ? They've piqued my curiosity...
|
[
"From my understanding you'd still feel an attraction, but instead of the magnets attracting each other, you'd feel the Mu-metal interacting with the magnets individually. ",
"If you got an old hard-drive laying around, rip it open take out the silver metal piece on the drive (",
"http://www.youtube.com/watch?v=3aVxB9oXcEc&feature=fvw",
") and try it out. If I was at home right now I'd go try it for you, I'm curious now."
] |
[
"Where is the mu-metal in a hard drive?"
] |
[
"Well you got me, I don't think its actually mu-metal being used in everyday hard drives, but I am sure it's some kind of shielding and all magnetic shields work the same by providing the magnetic field a really easy path to travel through instead.",
"Well I get a chance, I'll certainly poke around to find out. THE TRUTH "
] |
[
"Why does hot water freeze faster than cold?"
] |
[
false
] |
[deleted]
|
[
"Basically - it doesn't. But if you leave the same volume of hot and cold water out the hot water will freeze first because 1) lots of the hot water evaporates, 2) the hot water shrinks slightly as it cools, so basically there's less water. You end up with such a smaller volume of water in the pot that was originally hot that it actually freezes first (as it has a greater surface area to volume ratio so heat transfers out more quickly). ",
"Sorry, that's written pretty ugly but it's right!"
] |
[
"Check out ",
"this article"
] |
[
"It can actually, it's one of the most famous experimental findings in physics because it was so against conventional wisdom, it's called the 'Mpemba effect' after the Tanzanian school kid who first discovered it in a school lab study on ice-cream in the 1960s. ",
"http://news.discovery.com/tech/water-freezing-point.html",
"http://en.wikipedia.org/wiki/Mpemba_effect",
"This is one theory as to why it happens, positing that heating acts on the 'nucleation sites' around which ice forms, causing ice crystals to form more quickly. "
] |
[
"The video game \"Subnautica\" depicts an alien planet with many exotic underwater ecosystems. One of these is a \"lava zone\" where molten lava stays in liquid form under the sea. Is this possible?"
] |
[
false
] |
The depth of the lava zone is roughly 1200-1500 meters, and the gravity seems similar to Earth's. Could this happen in real life, with or without those conditions?
|
[
"Oh shoot! As a geoscientist and a huge Subnautica fan, I'm sorry to come in late on this.",
", the lava depicted in the lava zone is completely unrealistic (but ",
" cool.) Let me comment on the pieces of the answer that people have already given:",
"As ",
"/u/Little_Mouse",
" points out, real underwater volcanism on Earth doesn't have much glow to it: the water cools the lava so fast that it's almost all dark except for a few glints of red. Their video was taken at shallow depth by a scuba diver: here's a video from 1 km deep, similar to the lava zone in Subnautica:",
"https://www.youtube.com/watch?v=hmMlspNoZMs",
"No glowing pools, no red lava falls. Water is a fantastic reservoir for heat, and the fact that warm water rises lets it carry away heat by convection really ",
" well.",
"/u/PresidentRex",
" has a great analysis of pressures and the phase diagram of water, but there's one thing they didn't realize: ",
", as shown in the graphs ",
"here",
". Thus, there will be no \"stable layer of supercritical water\": it would be buoyant, rise, and be replaced by cool water, carrying away heat by convection.",
"What if the layer of water near the lava surface had a ton of salts dissolved in it, so it was denser? As ",
"/u/Bassmanbiff",
" points out, the thermal radiation law applies to ",
", not just rock: the supercritical water layer ",
" would glow. But that's clearly not what we see in Subnautica, and in any case the water above this layer would still convect, rapidly cooling it just as if it were lava itself.",
"Finally, as ",
"/u/UniqueUserTheSecond",
" points out, there's a thermometer in the game, and it reads 70 degrees C in the active lava zone. That's probably a reasonable temperature, actually -- note that in the video I linked to, the submersible isn't damaged by the volcano's heat, and ",
"/u/Little_Mouse",
" 's video was taken by a scuba diver swimming just a few feet from the lava! But this is nowhere near the temperature at which stuff starts to glow -- no matter what stuff.",
"As a side note, several people are commenting on air pressure and O2. One thing's for sure: the way Subnautica handles air and breathing at depth is completely wrong, and trying to dive the way you can in Subnautica would kill you dead. Nobody in the real world has done a dive on pressurized gas to a depth greater than 700 meters, the people who've done it to a depth below 100 meters only do so with hours of preparation, a special gas mixture, and slow cautious pressure changes, and even then many people who've tried to dive below 300 meters have died. The vehicles and seabases behave as if they are at sea-level pressure (if they weren't, they wouldn't implode if you take them too deep), but you can't just hop from 800 meters of pressure into your sea-level pressure vehicle without dying immediately. And let's not even talk about how moonpools work....",
"Of course, a realistic approach to lava and air pressure wouldn't make for nearly as fun a game!"
] |
[
"I can't speak directly to lava coexisting next to saltwater at depth, but there's some other misinformation thrown about this thread that I wanted to clear up:",
"Lava glows because of ",
"thermal radiation",
". This is linked with the concept of blackbody radiation, where matter emits electromagnetic radiation based on its temperature. All matter emits this radiation above absolute zero, but the color becomes visible to humans around 800 K (980 °F/526 °C) as a dull red. As temperature increases further, objects appear yellow and then white hot (possibly with a tinge of blue).",
"The in-game lava is a deep red, so it's likely on the lower end of visible thermal radiation (800 - 1000 K). So while it's possible the lava doesn't have the same composition as typical earth-like lavas, it can't have a temperature much lower (e.g. lead melts at 600 K, but you can melt lead without it emitting a red glow).",
"The planet in Subnautica could have an atmosphere of anywhere between about 0.4 to maybe 5 atm of pressure. The partial pressures (pp) of various gases in the atmosphere are the important part for humans. ",
"Partial pressure",
" is neat because if you take out the percentage of each gas in a gas mixture, the partial pressure would be equal to that percentage. Earth's atmosphere is (currently) 21% oxygen and basically 1 atm at sea level; that means that the oxygen has a partial pressure of 0.21 atm. On Mount Everest with a pressure around 0.33 atm, that's 0.07 atm of oxygen partial pressure. We need about 0.15 atm of partial pressure to breathe over the long term, but we can survive in less for brief periods (minutes/hours). ",
"On the other extreme, our bodies would suffer if the ",
"composition in a high-pressure environment was not just right",
". Non-noble gases start having detrimental effects at high partial pressures - including oxygen. Oxygen-related problems can start at 0.3 atm pp (aside from a risk of fire, this is one reason why we don't use 100% oxygen atmospheres at earth-like pressures in spacecraft), but up to 2 atm can be used ",
"for short periods",
". Carbon dioxide starts negatively affecting us around 0.06 atm of pp. Nitrogen narcosis is also well known in diving circles. The only somewhat safe options are neon and helium, and they can even start affecting our cell structures at extreme pressures. This really only applies to a human on the surface breathing air, though. ",
"(Tiny edit: I should note that these pressure calculations are based on normal earth gravity. Higher gravity means more pressure for equivalent depth; lighter gravity means less pressure for equivalent depth.)",
"Atmospheric pressure ends up being of little concern once you get deeper. The water pressure exerted at 1300 m of depth is about 130 atm. Adding 0.5 or 4 atm on top of that is miniscule. Water at normal temperatures is still just a normal liquid at this pressure (as we can experience here on earth diving into deep ocean trenches). Nobody is really going to dive that deep on a regulator though; you'd need a pressurized tank to breathe (otherwise the water pressure would collapse your lungs) and the gases will do unpleasant things to your blood and body once you start breathing gases at those pressures. There are reasons the current free dive record is 214 m and the scuba record is 333 m. ",
"As an explanation for the ",
"phase diagram for water",
": Temperature is the horizontal axis (in Kelvin); pressure is the vertical axis (usually in Pa and/or bar). The basic ice/water transition is the vertical line around 273 K (0 °C, naturally). In the big graph on that page, E is basically normal earth conditions (293 K or 20 °C and about 1 atm or 1 bar of pressure). Pressure in water (like any fluid) increases with depth. The rule of thumb is 10 m of water = 1 atm of pressure (technically it's 10.33 m = 1 bar, but everything else I wrote is in atm and 1 bar is just about 1 atm). This means you increase pressure by 1 atm each time you go another 10 m down.",
" ",
"Water is a normal liquid at 130 atm at standard temperature. Water is a supercritical fluid at 130 atm at 800+ K. (I wouldn't recommend swimming in it; it'll do unpleasant things to your body other than just burning you). This means it will be stable and won't turn into steam because it's already a weird mixture of steam and water. Unfortunately, my chemistry isn't good enough to tell you how salt is going to affect this in detail (other than to say that solids tend to dissolve better at higher temperatures and pressures so it could be denser).",
"So, at the very least, it's at least plausible for the lava to sit there covered in a layer of supercritical, denser saltwater."
] |
[
"The other possibility is that if the rocks are certain mixtures of lead and/or mercury and other low melting point metals, the lava could be much cooler than it is on earth. Some have melting points around 30 C."
] |
[
"Does light travel forever?"
] |
[
false
] |
Does the light from stars travel through space indefinitely as long as it isn't blocked? Or is there a limit to how far it can go?
|
[
"As long as it doesn't get absorbed by something, then yes, light will continue to travel indefinitely. However, due to the expansion of the universe that light wave will get stretched out along with the space it travels through, becoming lower in frequency and energy. This is why the Cosmic Microwave Background, which began its existence as ",
" visible light emitted very shortly after the Big Bang, has been reduced down to microwaves after traveling through space for ~13.8 billion years.",
"Edit: Wrong spectrum."
] |
[
"There is no \"point where the big bang occurred\". It happened everywhere at the same time. The microwave background is the light released when the big bang happened, but the points we see it from were ~13.8 billion lightyears away, so it took this long for that light to get to us."
] |
[
"There are definitely places that light will never reach, assuming that the expansion of the universe holds at a certain distance the other object is moving away from us faster then the speed of light (bending spacetime is the only thing that can go faster than the speed of light), so the light will never reach that point. "
] |
[
"[Physics] What happens when light is absorbed?"
] |
[
false
] |
Follow-up question on the "what happens to the photons" question. No doubt probably one I should know the answer to. What actually happens at atomic level when photons get absorbed?
|
[
"The photon is destroyed and its energy and momentum are given to whatever absorbed it."
] |
[
"But how exactly does it cease to exist? Like a bubble popping? Does it tear up into pieces? "
] |
[
"The energy of a photon is given by E=hf. An atom consists of a positively charged nucleus, with surrounding electrons. These electrons can only occupy some discrete orbitals, each with its specific energy level, where the lowest energy levels are closest to the center. If the energy of the incoming photon equals the difference between two energy levels the photon gets absorbed and the electron jumps from a lower energy level to a higher energy level."
] |
[
"Why does my pulse feel \"stronger\" on an area of my body that I recently injured?"
] |
[
false
] |
By "stronger," I'm trying to convey that it feels much more noticeable. For example, I broke in some new shoes, yesterday. This caused a blister on the back of my foot, which burst and exposed the raw skin underneath. Afterwards, I noticed that sensation that the movie "Elf" described (rather well, actually!): "My finger has a heartbeat."
|
[
"Inflammation is a response to injury; and that inflammation is due to increased blood flow to get nutrients and materials to the damaged site. More blood flow is what allows you to feel the stronger pulse."
] |
[
"Inflammation leads to increased blood flow - not the other way around. "
] |
[
"I apologize if I was incorrect, I'm not sure which leads to which. Although the answer in jest does explain why the asker can feel their pulse more strongly."
] |
[
"My seven-year-old would like to know if gels have a \"skin\" (meniscus) like water does?"
] |
[
false
] | null |
[
"A meniscus is caused by the ratio of the strength of the cohesive forces of a fluids molecules to each other and the cohesive forces of the fluids molecules to the container wall.",
"If a fluid has a higher cohesive force attracting it to a container wall than the intermolecular forces then the fluid will have a concave meniscus.\nIf a fluid has a lower cohesive force attracting it to a container wall than the intermolecular forces then the fluid will have a convex meniscus.",
"Since gels behave is a solid-liquid hybrid way, the presence or absence of a meniscus would most likely depend on the physical properties of the gel. It really depends on weather the cohesive forces described above are enough to deform the gels structure.",
"TL;DR: It depends on the gel. 'Fluid' gels such as shower gel stand a much greater chance of presenting a meniscus than 'solid' gels like ballistics gel."
] |
[
"It has to do with surface tension, which tries to maintain the smallest surface area possible. Mercury has a high surface tension, so it tries to form itself into a sphere. The material also matters, if the liquid is more attracted to the container than itself (like glass and water, both polar) the liquid tries to maximize it's contact with the container. "
] |
[
"I was looking at a pressure measuring instrument in the lab full of mercury and remember seeing that the meniscus was inverted (i.e. convex upwards in the tube). Is this due to it's high density?"
] |
[
"Why do we get frustrated?"
] |
[
false
] |
[deleted]
|
[
"Just because we do it, doesn't mean there is an evolutionary advantage or that it is even related to evolution.",
"We get frustrated because we are inherently selfish beings who want to succeed. Failure to succeed or proceed at a pace we like causes frustration."
] |
[
"Birds can get frustrated, for a certain definition of frustration. Parrots can redirect aggression on objects or other birds when prevented from doing something they want to do, and several shorebird species will get stressed about neighbouring birds being too close and vent their frustration by destroying inanimate objects e.g. shredding plants (this has no effect on the distance of their neighbours and so can't be said to be a territorial-defense mechanism).",
"Dogs and horses will also act frustrated when prevented from completing a behaviour. This is especially noticeable during training, when dogs will vocalise loudly and undertake displacement activities when thwarted in some attempt or other."
] |
[
"Yes, think of it more like a consequence of our need to succeed. It's the pain we inflict upon ourselves to as a sort of \"punishment\" for not doing things right. It can be irrational, sure, but it's the result of our need to succeed."
] |
[
"Are hive insects incestuous? If so, how do they deal with inbreeding?"
] |
[
false
] |
A thought just hit me and got me wondering. Bees, ants wasps, etc. have one queen who produces all of the hive's offspring. I'm not sure how it goes with ants but IIRC with bees the queen regularly mates with drones. Are these drones that hatched from the queen's own eggs? Does this lead to inbreeding? Or do drones regularly visit other hives? Edit: Thanks for all the awesome answers guys! The same question really goes for flightless insects too. I'm guessint it'd be a lot harder for a male ant to go about and find a queen he's not related to have invertebrate sex with.
|
[
"Are these drones that hatched from the queen's own eggs? Does this lead to inbreeding? Or do drones regularly visit other hives?",
"The queen uses sperm from drones from another colony. But these drones do not fly over and visit the colony itself. The queen mates during one mating flight early in her life. Sperm is stored at that moment and used for the rest of the life of the colony. Many worker individuals come from unfertilized eggs the queen lays, but they don't reproduce.",
"So no, they are not inbreeding at all. The entire point of the mating flight is to cross genes over a sufficiently diverse geographic distance."
] |
[
"Actually, worker bees are females and are produced from fertilized eggs. Drones are produced from unfertilized eggs. In certain situations (a queenless hive), a few workers can start laying eggs but since they're not fertile eggs, the hive will eventually be filling with drones which leads to eventual loss of the colony. Drones don't collect nectar or pollen, nor do they have stingers, so they cannot defend the hive. They live to reproduce and eat honey. "
] |
[
"They live to reproduce and eat honey. ",
"Sounds like my kind of life!",
"How does an unfertilised egg create an animal that can reproduce? That's the first instance I've heard of it in nature, is there some sort of unusual biology here or did I just not pay enough attention at school? An unfertilised chicken egg for instance just contains the yolk and white, right?"
] |
[
"Why does an infinitely-powered, constant-thrust spaceship never reach 300km/s?"
] |
[
false
] |
We have a spaceship that gets its energy in some unknown way, but it's essentially constant and unending and results in the spaceship not having to carry any fuel. With this energy, it can generate a constant amount of thrust indefinitely. The amount of thrust never varies for as long as the spaceship is traveling. A series of checkpoints is setup in space with each checkpoint 1 million km apart. Each checkpoint records when the spaceship passes by and transmits this time to all of the other checkpoints. The time is synchronized. The average speed of the spaceship is calculated by 1 million km / (end time - start time). The average speed between the first and second checkpoint is calculated to be 100km/s. The speed between the second and third is calculated to be 125km/s. Between the third and fourth, it's 150km/s. At this rate, it wouldn't take long before the spaceship will be going 300km/s. Yet that will never happen. I acknowledge that it's impossible for the spaceship to ever reach that speed. But there's no forces resisting the spaceship as it travels. It has unlimited fuel so that never runs out. It outputs a constant amount of trust, which would give it constant acceleration. Since it can never reach 300km/s, though, that means that at some point, the spaceship stops accelerating, even though none of the conditions have changed. Why? What physically keeps it from accelerating? EDIT: I recognize that variants of this question have absolutely been asked before, but those are invariably answered with variations of "frame of reference" or "not possible to have that much fuel" or similar. I have not seen an answer to this particular question anywhere in AskScience.
|
[
"Hi ",
"/u/az_liberal_geek",
",",
"it can generate a constant amount of thrust indefinitely",
"Sure, we can allow this. Let's pretend we have a constant thrust: our fuel is massless, the engine is perfect, and so forth.",
"It outputs a constant amount of trust, which would give it constant acceleration.",
"This is the misconception that leads to the incorrect answer. The reason this is incorrect is, in some sense, very Newtonian. I'll touch on this in the end, but try to keep this in mind as you read further.",
"When we're doing just special relativity -- our metric is the ",
"Minkowski metric",
" -- we like to do physics in inertial reference frames. In such a frame, an observer looks at the accelerating rocket and notices that its wordline is curved. In particular, it notices that its \"relativistic mass\" is changing. This is definitional, and I'll explain why:",
"I'll begin with a lightning-fast introduction to special relativity. An inertial reference frame is defined so that the ",
"four-velocity",
" is constant. The four-velocity is like the three-velocity you're used to thinking about, only now it contains a time-like component because we're doing relativity. If you look at the components of the four-velocity, ",
"they're all multiplied by this factor of ",
"[; \\gamma ;]",
". That factor is the ",
"Lorentz factor",
", which depends on the velocity of the object relative to an observer. As the object tries to reach c relative to the observer, ",
"[; \\gamma ;]",
" goes to infinity. Maybe you can start to see where this is going.",
"There are two force vectors we need to talk about. The first is ",
", the ",
"four-force",
" that the rocket sees from the engines. The second is ",
", the three-force that tells us information about the actual acceleration of the rocket in the spatial coordinates. Notice that the ",
"four-acceleration",
" ",
", which is related to ",
" by ",
"=m",
", depends on the three acceleration ",
". But ",
" is directly related to ",
" in the Newtonian sense that ",
"=m",
". (All throughout this, I've assumed m is a constant because I'm using massless fuel.)",
"Now when we fix the thrust ",
", it's true that we fix the force we apply to the rocket with the engines. It's ",
" true, however, that the spatial acceleration ",
" of the rocket is likewise fixed. In Newtonian mechanics, the thing \"resisting\" acceleration is the mass of the object. You probably know this from experience: pushing a box full of textbooks is harder than pushing an empty box. However, in Newtonian mechanics, you can in principle apply the same spatial acceleration forever. ",
"Mechanics in special relativity differs from Newtonian mechanics here. In special relativity, accelerating an object becomes increasingly more difficult as it speeds up because its \"relativistic mass\", ",
"[;\\text{m}_{rel}=\\gamma m_{rest} ;]",
", is increasing, and ",
" (the term we called ",
") ",
". In order for the spatial component of ",
", ",
"[; \\gamma_{\\bf{u}}^2\\bf{a}+\\gamma_{\\bf{u}}^4\\frac{\\bf{a}\\cdot\\bf{u}}{c^2}\\bf{u} ;]",
", to remain constant, ",
" must go to zero as ",
"[; \\gamma ;]",
" goes to infinity, and ",
" is the spatial acceleration of the rocket. In short, we've fixed ",
", but we did not fix ",
". Thus, the rocket does not keep accelerating spatially at a constant rate despite the application of a constant thrust by the engines. Indeed, ",
" will approach zero as the speed of the rocket approaches c.",
"You may be wondering why we can't fix ",
". The reason is this: ",
", what we call the \"proper acceleration,\" is the fundamental quantity. It's the \"true acceleration\" that the engines apply to the rocket. It's the thing we have control over. It's the thing accelerometers measure. You can't get a uniform ",
" without an infinite force.",
"NB: Physicists don't like talking about the \"relativistic mass\" of an object because it's frame dependent and because it comes from treating the four-momentum like the three-momentum. Physicists like frame invariant things, like the \"rest mass\" (what we now just call the mass). They also like to distinguish the properties of the four-momentum from the three-momentum. I appreciate and agree with these points, but I think for the sake of brevity it's better to talk about relativistic masses here than to get distracted with the nature of four-vectors and so forth. Suffice it to say that rockets don't actually gain mass and \"relativistic mass\" is conceptually misleading. The math is all the same, but the interpretation differs. The utility of the above explanation is in the analogy to Newtonian mechanics."
] |
[
"The short answer is, as the spaceship gets to relativistic speeds its mass begins to increase, so the constant thrust results in less and less acceleration. Increasing the thrust won't help because as you approach light speed, the mass approaches infinity.",
"From inside the spaceship you wouldn't notice this mass increase, however. The 1 million km markers would appear to keep coming faster and faster, and eventually they'd fly by often enough that you could seemingly clock yourself as superluminal, however at the same time the markers would appear to be closer to each other -- from your frame of reference they'd be less than 1 million km apart, meaning you're not superluminal after all. From the outside world you'd be passing the markers slow enough to be subluminal, but everything inside the spaceship would be observed moving in slow motion, which is consistent with observers inside the spaceship seeing the markers flying by more frequently."
] |
[
"But let's say we are one of the observers at a checkpoint and have a way of measuring the mass of the spaceship as it passes by. Would the measurement show 1,224,321 kg?",
"It depends on how quickly that observer is moving with respect to the spaceship. If the observer shares an instantaneous comoving rest frame with the spaceship at the point where the ship passes the observer, then the observer will identify the first component of the four-momentum -- the \"relativistic mass\" -- as identical to the mass (\"invariant mass\" or \"rest mass\"). If the observer is comoving with the observer that was at rest with the spaceship when the spaceship began to accelerate, then the second observer will agree on the relativistic mass. All of that said, I want to be clear that both observers will measure the same ",
". I say this because I notice you're already using the shorthand \"mass\" when referring to \"relativistic mass,\" and I want to be clear that these two things are not the same.",
"And -- where is it coming from?",
"The nature of relativistic mass is such that it is velocity dependent. This is what distinguishes it from the mass of the object. When computing the first component of the four-momentum of the spaceship, one finds that it equals ",
"[; \\gamma m_{rest}c ;]",
". Up to the conversion factor of c, this is the relativistic mass, i.e. ",
"[; m_{rel}=\\gamma m_{rest} ;]",
". The velocity dependence comes from the Lorentz factor."
] |
[
"Does hot food provide more energy than cold food?"
] |
[
false
] |
Say I have two identical dishes, but one is hot and one is cold. Does the hot one provide more energy to my body than the cold one? I know the dishes have the same amount of calories in the food itself, but if heat is for this purpose energy, wouldn't a dish that is hotter than my body temperature disperse that energy to my body? If I'm in a room with a temperature below my body temperature, would this mean I get more energy from the food since the hot food provides heat rather than my body burning calories to generate body heat? Essentially, does this mean heating your food gives you more energy?
|
[
"It is true that eating hot food will lessen the calories your body needs to burn to maintain body temperature. The extreme would be drinking ice water which has no calories and would chill you, requiring you to burn calories.",
"But the effect is small. To raise the temperature from 0 C to 40 C, you need 40 calories (lower case) for each gram of water. A cup of water is about 240 grams, so that's 9600 calories, or 9.6 kcal, aka food Calories (upper case). That's like a half teaspoon of sugar, or less than one peanut or one potato chip."
] |
[
"While completely factual, you are missing the efficiency factor for food intake versus heat generation in the human body."
] |
[
"The question is not as silly as some people might think. Naturally it is true that warm food contains more energy than cold food. In a sense heating up 200 grams of food from 10 C to 60 C “infuses” it with about 10 kcal extra. That is not much though, and I would bet that in total the difference in effective energy absorbed by the body is significantly smaller than even that."
] |
[
"Is there any trait or property that Earth lacks that would have made life even more likely to develop on it?"
] |
[
false
] |
[deleted]
|
[
"We know so little about how life actually started that it'd be mostly speculation to guess at what would increase the odds. That said, here would be some guesses:",
"Because we don't know how life forms or what stages it takes to get to something resembling a modern cell, it's hard to say if any of these things would actually promote or hinder life from evolving."
] |
[
"I believe the original question was about the probability of ",
" life developing on a planet. Maybe another kind of life than what we find here on Earth is more probable to develop its respective environment. Maybe another planet lacks some of the hurdles early Earth life might have had to go through. I don't think the OP specified ",
" life in the question.",
"Of course, if you define \"life\" in very narrow terms, it could very well mean only the kind of life that Earth has developed, but I don't think that's necessary.",
"Please note that I don't really know anything about the subject, I just thought you missed the point of the question. If you have some input on the issue, I'd love to hear it!"
] |
[
"There have been times in Earths history where Russia was indeed closer to the equator and probably had a lot of forests during those times. There are also periods where the Earth was in a hot house like the Paleocene and the Eocene. During times like these vegetation would be able to thrive with the increase in carbon. "
] |
[
"Why do computers sometimes move slowly?"
] |
[
false
] | null |
[
"I don't have time to give you the whole story but a common reason is that the computer is \"blocking\", is, waiting for a resource. Say you have two programs running, and both need access to the hard disk. The disk can only change one thing on the disk at a time and it takes time to move the head from one place to the other. The computer will try to satisfy both requirements by moving the head back and forth but it will lose performance in the process."
] |
[
"I don't mind that it's not the whole story. I appreciate your response. I've always wondered what it was - in relatively simple yet still sophisticated terms - what's actually going on inside the computer when poor old MacBook has the spinning rainbow wheel."
] |
[
"The real mystery for me (I am a software engineer) is how software keeps track with hardware in keeping computers slow. My slow laptop is a supercomputer from 20 years ago, yet it still takes six seconds for the unity main menu window to display on the screen. I got better subjective performance out of a PDP 11/84 running at 1Mhz. Admittedly the laptop running ubuntu does a lot more work, paining a nice window on the screen with transparency, etc, but another part of the story is the way software is developed now. Where in the past a program might have read like the following:",
"Now they read like this:",
".",
"It is awful stuff to debug and it runs very slow. The sad fact is that software expands to fill the available hardware."
] |
[
"When losing weight, how does the body choose where to pull fat from?"
] |
[
false
] | null |
[
"When we burn fat our fat cells start turning the fat they store into fatty acids which can then be transported by our blood causing the fat cells to shrink. The fatty acids don't come from one specific place, all our fat cells start pumping out fatty acids. How much comes from specific area is determined largly by genetics and not like many people seem to think by the muscles you are using during excercise. So cycling won't make your legs any slimmer than it will make your arms."
] |
[
"If I understand you correctly then no I don't think so, excess visceral fat (fat stored inbetween your organs) does tend to get burned up first though. Your body also maintains a thin layer of fat directly under your skin that you only tend to lose under severe malnutrition, it's more kept as insulation than as energy storage."
] |
[
"Does the surface of the fat store matter? ",
"Bit hard to explain I guess but would you lose more fat in area's that do not have surrounding fat? I mean let's say if you have a lot of belly fat, would the \"inner\" most cells of your belly fat release less fatty acids then the ones more closer to the skin / insides?"
] |
[
"We often hear that the majority of the ocean is unexplored. Are we trying to change that and if so, what are we exploring and finding?"
] |
[
false
] |
As the title says. I've often heard that we know more about the moon than we do our own ocean. Are we actively trying to change that and if so, what are some of the exciting projects ongoing which are giving us some new insights in the oceans.
|
[
"We are literally ",
"live-streaming",
" right now from the bottom of the ocean, from hydrothermal vents on the East Pacific Rise. There are often live events like this, check out ",
"Nautilus Live",
" also some time, from the Ocean Exploration Trust.",
"There is a big push to map, explore and characterize the ocean in the US EEZ.",
"There is an international effort map the entire ocean, ",
"SeaBed 2030.",
"Yes, there is better ",
" of the surface of the moon, or mars, than of the seafloor. However, we ",
" a lot more about the seafloor than those. There are many tons of samples, detailed 3-dimensional sub-seafloor images, models for oceanic crust formation and recycling, etc. that are simply not possible with current information for the moon or mars.",
"Any metric for knowledge, other than high-resolution pictures, demonstrates the depth of understanding of seafloor processes."
] |
[
"Then why do I hear that asserted in many reputable documentaries? ",
"Because its a good sound bite and its a vague enough claim it can be made without factual evidence either way to back it up or refute it on the part of ocean advocates."
] |
[
"If you can provide examples of what you describe I would be happy to address them. It's what I do, and the firs time I went to the bottom of the ocean was in 1992.",
"I too hear reputable claims there are better images of the surfaces of the moon and mars than the bottom of the ocean. This is true, and I don't at all regret how it motivates people to support oceanographic research. It is not, however, true, we \"know\" more about those places. ",
"It is incomparable how much more knowledge we have about the seafloor."
] |
[
"AskScience, what part of Earth has the smallest average temperature range? What part has the most hospitable temperature range?"
] |
[
false
] |
Obviously, all parts of the globe have fluctuating temperatures, and "hospitable" is somewhat subjective. I'm curious about places that don't change much or stay in a comfortable range.
|
[
"I'm not going to try and answer the part about 'most hospitable' -- humans live all over the planet, and people express preferences for tropics, mid latitudes, or snowy climes. ",
"Average temperature range, though, I can do. Using the NOAA land temp ",
"data",
", I made a map of the areas of the globe with the most temperature variability in monthly means from 1948 to 2011. It's ",
"here",
". ",
"You can see that the tropics are the most stable region and the arctic has large fluctuations. The scale is standard deviation in degrees Celsius."
] |
[
"Thank you, thank you, thank you for delivering. Have some gold!"
] |
[
"Awesome! Thank you!"
] |
[
"Is it possible to measure a liquids specific gravity in space?"
] |
[
false
] |
Or how is the density of small objects determined without gravity?
|
[
"Inertial mass is the same as gravitational mass, so you can measure the mass of something in space by, say, spinning it around and measuring the resulting centrifugal force."
] |
[
"If you were to fill a container (of known mass, or mass you determine using the following) with that liquid, then attach the container to a spring of known spring constant, and then set the spring into motion (ie pull the mass a bit away, then let the mass oscillate), you could determine, from the motion of the spring, what the mass is attached to the spring. "
] |
[
"In the analytical labs best equipped for specific gravity of liquids, a digital densitometer of the ultrasonic type is employed to routinely determine precise measurements of liquid density.\nDensity varies inversely with temperature for liquids over almost all ranges, so both density and specific gravity need to be notated with measured temperatures to be accurate.",
"Specific gravity is mathematically determined from measured density.",
"In the ultrasonic densitometer, the propagation of a high-frequency sound wave through the sample is measured. That property is fundamentally dependent on density, with some influence by viscosity, and has been highly correlated to correct for the known cases of deviation due to viscosity.",
"check out:",
"http://www.anton-paar.com/",
"Their instruments should ideally work in space or in terrestrial locations having various local forces of gravity, without further correction for the pull of the Earth itself since they are calibrated against known materials.",
"Keep in mind that specific gravity is not density.\nThe numbers are usually similar to each other, but there is a mathematical reason for the difference.",
"Density is a fundamental measurement of mass/volume, so in addition to temperature, units of measurement need to be included such as g/ml for metric or lbs/gal for USA.",
"Specific gravity is a unitless number.\nSpecifc gravity is the density of the sample divided by the density of water, or in the simplest legacy technique, the weight of sample divided by the weight of the same volume of water.\nNotice how things like actual units of weight or volume do not matter in specific gravity, as long as the temperature is the same between two locations, the measured weight of sample divided by the measured weight of the same volume of water will give the same result. One location could be Metric and the other English. This is also independent of gravitational strength (and air buoyancy since both sample & water measurements were of the same volume), provided there is at least enough gravity to operate a weighing balance.",
"Normally when measuring density, the temperature of the measurements are specified to some conventional standard recognized for a particular type of liquid or industry.\nWhen reporting specific gravity, both the temperature of the sample and the temperature of the equal volume of water are assumed to be the same unless specified otherwise.\nThe best nomenclature always specifies the actual temperature for density, and two actual temperatures for specific gravity.",
"Such as 0.7815 grams/ml at 20 degrees C for density",
"or Specific Gravity 0.8842 20/20 which means density of sample at 20 C divided by density of water at 20 C",
"or Specific Gravity 0.7654 20/4 which means density of sample at 20 C divided by density of water at 4 C",
"This 20/4 convention arose largely to minimize the numerical difference between Metric density and specific gravity at 20 C, since water has its greatest density at 4 C and it approaches 1.0 g/ml at that temperature, it's like dividing the density in g/ml at 20 C by a factor of 1.",
"For critical work with either specific gravity or raw density, when actual weighings are involved, a correction needs to be made not just for local gravitational pull, but also for the buoyancy of the air displaced from the container by the sample at the temperature, humidity, and altitude of the measurement.\nThese most critical measurements then require further details in reporting such as density \"in vacuo\" or alternatively \"in air\". Many times this detail is not available even for reference literature, but sometimes can be inferred from different industrial or local traditions.\nTheoretically or ideally, specific gravity is supposed to always be calculated from densities in vacuo.",
"The vacuo thing has nothing to do with outer space, and no measurements are routinely made in a vacuum, the buoyancy from the mass of the same volume of actual air is simply added to the sample's measured mass in air to result in the mass in vacuo."
] |
[
"How do radio stations know how many receivers are listening to them?"
] |
[
false
] | null |
[
"They don't.",
"They do a poll.",
"They look at a map and say \"there are 3.5 million people in the area where they can easily listen to this radio station, let's call 3,500 of them and ask them if they've listened to the station in the last week.\"",
"So they do it, and they find out that 173 of the 3,500 people have listened to the radio station in the last week.",
"So they figure that 173/3,500 = 0.0494 is the fraction of people in the area that listened to the radio station in the last week. Then they multiply by the total number of people in the area: 0.0494 * 3,500,000 ~ approximately 173,000 listening in the last week.",
"With something like cable TV, you can get direct data, because the cable box can report back to the cable company what channel is being watched, but with broadcast radio/TV, there isn't any effective way to tell."
] |
[
"Nevertheless, that's how it's done.",
"Here's the Wikipedia article on the dominant polling company for TV viewing in the US and their system:",
"https://en.wikipedia.org/wiki/Nielsen_ratings",
"Note that it's a little more complicated than just a phone call - they have people either keep diaries of viewing habits or install a little machine on their TV that records viewing habits."
] |
[
"And yet I have never been polled for this and I don't know anyone who has. ",
"I got called by Nielsen about 6 months ago and they mailed me a $5 bill for answering their survey, so now you do know someone."
] |
[
"Why do electrons have a \"negative\" charge?"
] |
[
false
] |
I am reading an electronics textbook and it is talking about the confusion around electricity flowing from a positive charge when it is actually electrons flowing from a more negative charge. I've taken a few chemistry courses in college so I get the basics of protons, neutrons, and electrons. What I am curious about is this: why is the electron's charge negative? In my eyes, a negative charge is just the name for the opposite of a positive charge, and it is just a name. Is there something in the mathematics describing these particles that force a proton to be called positive and an electron to be called negative?
|
[
"No, it's just an arbitrary convention. The signs of the electric charges of the electron and proton must be opposite, but which one calls positive and which one calls negative is a matter of historical accident."
] |
[
"Like how it would make arithmetic just that bit easier if we counted in base 12. Oh well."
] |
[
"I can't answer your exact question, but the reason your electronics textbook says current flows from positive to negative is because (according to my high school physics teacher and Wikipedia) Benjamin Franklin, who kinda pioneered studies on electricity, believed that. Now, we know that it's actually electrons being moved in the wire (more or less) so chemistry textbooks will reflect that, but physics and electronic textbooks will still follow Franklin's conventions.",
"I'm sure there's no mathematical reason for specifically designating the electron as having a negative charge, it probably had more to do with the way the discoverer was invisioning the atom."
] |
[
"How can locks (as in door locks) or anything that requires a unique part be mass produced?"
] |
[
false
] |
I know some cheap locks only have a few unique keys and are just randomly sorted to give the illusion that they are unique. But how can locks that are expected to be at least moderately secure be mass produced while keeping every lock's key different?
|
[
"It doesn't take much variation to produce many unique locks.",
"The equation is:",
"Combinations = (unique pins) ",
"So if your locks use 6 pins and you make 10 different pin sizes then you can make 10",
" = 1,000,000 unique locks.",
"If you move from 6 pin lock design to a 7 pin lock design you can make 10 million combinations from your 10 different pins (10",
"If you want to make a seven pin lock for at least each person on earth you need to produce 26 different pins. (26",
" = 8,031,810,176).",
"The precision or size of a lock that can distinguish 26 pin sizes may be prohibitively expensive or large but that's a question for ",
"r/askengineers",
"."
] |
[
"I suspect that in olden times a key would be cut with a set of moveable dies, inserted into the barrel, then pins would be inserted in the holes and cut flush. Nowadays they probably have pre sized pins and a computer will insert the correct pins to match the key",
"Combination locks have notched disks that have notches in different places relative to posts that turn the disk behind it. The exterior is uniform, but there are enough unique disks and with three positions for them the locks are unique enough to protect your sweaty gym shorts."
] |
[
"To add on, car manufacturers don't make unique keys for each car. There might only be a couple hundred or thousand different keys for a particular model (meaning that your key has several twins). That's one of the reasons so many are going to completely digital systems, so you can make each individual \"key\" unique."
] |
[
"If you're travelling at 0.99c, would you still observe light moving away from you at c?"
] |
[
false
] |
EDIT: Thanks, I thoroughly enjoyed reading this discussion!
|
[
"Yes.",
"Also, remember, there is no such thing as \"travelling at .99c\" in the abstract; you might be moving at .99c relative to me, but you will experience yourself being at rest and me moving at .99c relative to you."
] |
[
"Yes, you can continue that process indefinitely. And there would be no observable difference between any of the steps of the process. If you couldn't see the stars or the people you left behind, there would be no way to know how many times you had sped up. That's a very important feature of space and time, that it is unchanged by velocity shifts like this (though the matter and energy will not be unchanged, it will all be moving to the left or whatever). This is called Lorentz invariance, and it's a property of all currently known physical laws(the velocity shifts are called lorentz boosts)",
"It's also true that no matter how many times you boost to .99c relative to the previous guy, you'll never be moving at more than 1c relative to the first guy. This is because space and time change relative to your speed, or another way to think of it is that forces get less effective on fast objects."
] |
[
"Yes, but instead of a .99c boost taking you from .99c to 1.98c, it would only take you to .99995c. That's what I mean by forces being less effective: the ship would be using the same amount of force for each boost, but it doesn't result in the same speed increase (relative to earth). But it always changes the speed at least a little bit."
] |
[
"Why don't batteries get drained instantly when shorted?"
] |
[
false
] |
Hi, I am starting to learn some electrical science and there is one thing that is confusing me. Each battery is rated for a limited amount of current hours (more geerally watt hours but the voltage stays constant so it doesn't really matter). The resistance of a short length of wire is incredibly small. This then means that the current will also be extremely high, since current is voltage over resistance. What I don't understand is why the battery doesn't instantly die when shorted. At first, I thought it was internal resistance, so I meassured the current through the contacts of a nine volt and got a value around 1 microamp. In my mind this would mean that the internal resistance is massive and the battery should be dead, but I put an LED on it and it lights. Am I measuring the current wrong? What prevents batteries from instantly draining when shorted?
|
[
"EE Here.",
"You're correct its internal resistance. Think of the real life battery as an idealized battery but with an internal resistor added. The resistor limits the current and prevents the ideal battery from draining immediately. Not sure I follow the experiment you tested that resulted in a microamp - thats definitely not enough to power an LED.",
"You are likely measuring the current incorrectly. Remember in current-sense mode, the multimeter has low resistance and should short the battery if you test the contact (do not try this). Also worth noting that many multimeters use a different plug for sensing current vs. voltage - perhaps the lead is in the wrong contactor.",
"",
"Edit: Another thought. A capacitor is effectively a low-resistance (and low capacity) battery. Given its low resistance it actually will discharge instantly when shorted. This rapid current sink / source characteristic is why capacitors are used to \"smooth\" out varying voltage levels in power converters."
] |
[
"Your mental model is that a battery is essentially a box of voltage: there's a whole pile of electrons available on one terminal and a paucity of them on the other. They're just waiting for a connection in order to rush over and equalize the potential.",
"This is what a ",
" is like, but not batteries. Batteries aren't just sitting on a huge pile of electrical potential. Instead, they ",
" chemical potential to electrical potential as needed in order to maintain a relatively fixed level of voltage. This ",
"electromotive force",
" is limited in how quickly it can generate voltage, so a battery doesn't discharge instantly if you short it."
] |
[
"You check the change in the voltage drop as you linearly increase the current. The internal resistance will cause increasing levels of voltage drop as the current increases."
] |
[
"How fast is the earth moving in relation to the center of the galaxy? Does that speed vary?"
] |
[
false
] | null |
[
"If the earth is 30 000 light years from the galactic centre and a ",
"revolution",
" takes between 225 and 250 million years it would make it's speed somewhere between 225 km/s and 250 km/s (kilometers per second). ",
"http://hypertextbook.com/facts/2002/StacyLeong.shtml",
"http://www.wolframalpha.com/input/?i=%2860000+light+years*pi%29+%2F+250+million+years"
] |
[
"Current estimates",
" are that the solar system has an orbital velocity of 251±15 km/s around the center of the Milky Way, and the Earth orbits the sun at about ",
"30 km/s",
". This means that depending on where the Earth is in its orbit, it can be moving either 30 km/s faster or slower relative to the center of the Milky Way (or 251±45 km/s). 15 km/s is uncertainty in measurement, and the other 30 km/s is due to the Earth's motion around the sun.",
"From measurement of the cosmic microwave background, we also know that the Earth is moving at ~370 km/s relative to the reference frame of the big bang (this is known as ",
"), so we can calculate the peculiar velocity of the Milky Way to be ~552 km/s (based on the numbers given above and a bit of trigonometry)."
] |
[
"That can be calculated:",
"T=To*γ where γ is the lorentz correction, γ = 1/sqrt (1-v",
"that would be 1/sqrt(1 - 552",
" = 1/sqrt(1-304704/90000000000) = 1/sqrt(1-0.0000033856) = 1/0.99999830719 = 1.00000169281",
"So that movement basically adds 53.4 seconds every year, or one full day every 1618 years.",
"pretty negligible.",
"obviously a few things must be corrected for the effect of various gravitational fields but still..."
] |
[
"How exactly does histamine improve tourettes?"
] |
[
false
] |
There was a study on mice recently that confirmed an earlier idea of histamine playing a role in tic behaviors. They've injected histamine directly into "striatum" to observe the effect. Stupid question - could you emulate the effect simply by consuming "histamine-rich" foods? Or would the mechanism be entirely unrelated? Thanks.
|
[
"Med student here. Lots of neurotransmitters come into play with every aspect of our psyche and mental status. Histamine definitely plays a role in this, as evidenced by the sedative effect of anti-histaminergic drugs (Diphenhydramine). I can't speak to this new study that you mentioned, but I can answer your second question.\nIt is unlikely that eating \"histamine rich\" foods would have any effect. It would likely be altered in the acidic environment of the stomach, thus decreasing its bioavailability. Secondly, it would have to gain access to the brain to have your desired effect, which requires crossing the blood brain barrier. This is a difficult task for polar molecules, but less difficult for lipophilic ones. Finally, histamine is a major role in allergic/anaphylactic response. By flooding your body with histamine, you would risk causing global inflammation, and possibly sepsis. \nIf you were to pursue this, your best bet would be designing drugs that increase the availability of histamine in the brain. Or perhaps some sort of lumbar puncture injection of histamine into the spinal fluid (but probably not a good idea).\nHope this helps, feel free to ask follow ups"
] |
[
"A report about tourettes study was published by a group of specialists from the Yale School of Medicine leded by Matthew State in The New England Journal of Medicine.",
"During the investigation, the scientists studied the hereditary information of family members in which Tourette's syndrome suffered a father and eight children. In all patients scientists found a similar section of the genome.",
"After analyzing this genome site the researchers identified a mutation of the HDC gene which is responsible for the production of an enzyme that regulates the synthesis of histamine. This substance is involved in the transmission of nerve impulses and regulates many vital functions of the body. The mutation of the HDC gene in patients with Tourette's syndrome caused a deficiency of histamine.",
"Scientists noted that according to previous studies mice with a lack of histamine were more prone to repeated actions similar to those in patients with Tourette's syndrome."
] |
[
"Well, maybe neuroscientists will find a way to inhibit the reuptake of Histamine, in a similar way SSRIs do to Serotonin. Or increase the production on neurons. \nOr maybe associate a lipophilic histamine that is able to cross the blood-brain barrier with an anti-histaminic that can't. "
] |
[
"Is E=MC² just a logical extension of F=MA with a different definition of terms based on discoveries unknown to Newton? ..."
] |
[
false
] |
or is it an equation which though seemingly similar describes a fundamentally different physical event? I know this may just be a pedantic question but it interests me nonetheless.
|
[
"E=mc",
" is a simplification of the full equation which contains a momentum term. That momentum term would better relate to MA, since an applied force over a given time would give you an impulse, or change in momentum. The mc",
" term describes the equivalent energy in a given mass at rest, which doesn't have anything to do with applied force or accelerations.",
"Edit; the full equation is E",
" = (mc",
" + (pc)",
" where p is momentum"
] |
[
"No need to retract the question, it was a good one. I'm an engineering student and every day I find myself seeing similarities in equations and trying to find out if they're related. Thats how a lot of the equations we have now were created, someone saw two separate equations and made some connections."
] |
[
"You remember newton's expression for the kinetic energy?",
"E = 1/2 m v",
" = 1/(2m) p",
"Well, this quantity is not really conserved in the relativistic limit. For very big velocities, the actual energy of the system must be written as:",
"E",
" = (mc",
" + (pc)",
"And in the slow velocity limit, it reproduces the form of the newtonian kinetic energy, plus a term which is just a \"rest energy\", which is given by mc",
" . So a body at rest also has energy, and it's given by mc",
" ."
] |
[
"Does the asthenosphere actually exist?"
] |
[
false
] |
I have been recently told (by high-school teachers, for what it's worth) that apparently geologists don't think the asthenosphere is a thing anymore. Having been through uni over 10 years ago, I could very well be out of date, but honestly, it came as a shock to me.
|
[
"I have no idea what they’re talking about. I teach tectonics at the university level and have not heard of this being a thing. There’s not exactly a source for demonstrating that the asthenosphere is still considered to be real, but there are hosts of papers published within the last few weeks that are still discussing the details of the asthenosphere, eg ",
"this one",
"."
] |
[
"There are certainly lots of outstanding questions related to the asthenosphere, e.g., how best to consider the lithosphere-asthenosphere boundary, percent melt in the asthenosphere, amount of hydration of the asthenosphere, details of its rheology, etc, but that's different than rejecting the concept of the asthenosphere and I've never seen any paper or even a hint of controversy in terms of the concept of there being a mechanically weak layer separating the mantle lithosphere from the rest of the mantle. It's deeply embedded in our understanding of the strength profiles of the lithosphere to upper mantle and an important part of the mechanism by which plate tectonics works (which requires a way for the lithosphere and mantle to be strongly decoupled). I would suspect they've gotten confused by something (e.g., correcting the misconception that the mantle is primarily liquid somehow led to them thinking that the asthenosphere doesn't exist?), but I can't honestly guess as to what. Arguments from authority aren't usually too helpful, but I'm a geologist with a PhD working on tectonic problems who is an active researcher at an R1 university and teach tectonics to masters and PhD students, so I kind of feel like I'd know if \"geologists don't think the asthenosphere is a thing anymore\"."
] |
[
"I know! I can't find anything either (at least in English, I found a Spanish paper called something like 'Goodbye to the asthenosphere' but it didn't say anything of use, basically that the asthenosphere is bad science). But they're so vehement about it! It made me feel like I know nothing at all."
] |
[
"Why do we like to destroy things?"
] |
[
false
] | null |
[
"to be honest you'd probably get better and/or more responses in ",
"r/psychology",
"."
] |
[
"Maybe even ",
"r/askphilosophy",
"?",
"As a layman, I fully believe the \"destruction as a form of creation\" thing. People like to be creators of something, make things change, and destruction is an easy way of accomplishing this."
] |
[
"That's just saying 'we like to destroy things' using different words. ",
"He asked why."
] |
[
"Do you have any stories about interesting/promising experiments that worked in the lab but not in the real world?"
] |
[
false
] | null |
[
"If you have some agar, you can show that many bacterial species cannot grow well on agar plates impregnated with various spices like garlic and cinnamon. Some things in those spices are antiseptic. However, like your example, it's all in vitro - these spices do not have curative properties, because they are digested etc. first.",
"If you do ever try this, please be forewarned: the smell of the impregnated agar as it comes out of the autoclave is absolutely horrible. It was like a sage and ginger wet nightmare."
] |
[
"My favorite is the ",
"Viagra",
" story.",
"It was initially made as a treatment for high blood pressure, and made it all the way to clinical trials. During the trials, it turned out to be completely ineffective at controlling blood pressure. However, the patients in the study noted that they were all getting erections. Pfizer was fine with this result, even if it wasn't at all what they were going for."
] |
[
"I guess a couple of people mentioned it then everyone would have been like 'shit me as well'"
] |
[
"Could you theoretically use the DNA from two sperms or two eggs to clone/create a human being?"
] |
[
false
] | null |
[
"You can do it with two eggs. Two sperm is a bit harder, since you'd need to grab an X chromosome from somewhere (YY would not be viable)."
] |
[
"I mean, half of the sperms are X chromosome while the other half are Y, are they not? ",
"Couldn't you just grab one or two sperms that are X chromosome to complete the process?"
] |
[
"Yeah sorry, I sort of thought myself into a corner there. You should be able to do it, although the sperm would be a little more difficult, since you'd need some 'normal' sized cell to put the genetic information into. Sperm are reduced cells, with reduced/missing organelles, so you'd have to basically remove the DNA from a normal cell, and pop in the genetic information from two sperm, making sure at least one of them had an X chromosome."
] |
[
"Do plants have stem cells and do they recombine their genes?"
] |
[
false
] |
These are two questions: Firstly do plants (if this is too general: trees) have stem cells, and if yes where are they located? Secondly does genetic recombination happen with plants, too? E.g. if two plum blossoms are pollinated by one same bee carrying the polls of only one other plum tree, are the developing plums genetically identical? Putting all hopes on you guys, as my biology teacher couldnl not answer them.
|
[
"Yes, in plants growth and the start of new plant organs takes place at cells called ",
"apical meristems",
". Generally there is a shoot apical meristem for shoot growth and a root apical meristem for root growth. Lateral branches often start with their own shoot apical meristems.",
"But that is just for growth and organogenesis. When it comes to other properties associated with stem cells, such as pluripotency, all plant cells possess them. You can take any cell out of a plant and , with tissue culture and plant hormones, get out a fully functional clone. Or a thousand clone plants. Tissue culture like this is big business in industry and can even be practised at home, see ",
"this",
" if you are interested."
] |
[
"For your second question, yes, genetic recombination does happen in plants. They have a slightly different life cycle to animals but they undergo meiosis in the same way to produce haploid spores. So the pollen and egg in flowering plants have come from meiosis and would make the new plants genetically different."
] |
[
"Thanks for the detailed answer, any knowledge on recombination concerning plants? "
] |
[
"A black hole that forms from a star collapse stores more information on its event horizon than was contained in the original star. Where did the extra information come from?"
] |
[
false
] |
In class we learned that event horizons basically store and grow with information. We also approximated the information stored in a black hole in relation to its mass/size. We were told that the amount of information stored in a black hole's event horizon is actually greater than the total information of the star that it originated from. Is this true, and if so, where did the extra information come from?
|
[
"You're discussing the ",
"Bekenstein bound.",
" Essentially, consider a box with entropy/information S. If you try to reduce the volume of that box below a certain point (Schwarzschild radius), it collapses into a black hole. From that point on, you cannot compress the box further for any action you do to it adds to its massenergy and entropy making the black hole bigger.",
"We were told that the amount of information stored in a black hole's event horizon is actually greater than the total information of the star that it originated from.",
"I've never heard this. Did you hear correctly? If we think about the collapse of a stellar core, just before collapse, the entropy of spherical volume must satisfy π(R+dr)",
" - S > 0. At the moment of collapse (dr→0) then πR",
" - S",
" = 0 and we have a newly formed black hole."
] |
[
"Information, like energy, cannot be created or destroyed.",
"This requires a settlement of the black hole information paradox aka how pure states can become mixed as well as a settlement on the nature of what wavefunction collapse really is."
] |
[
"Is this true, and if so, where did the extra information come from?",
"The current mainstream theory is that the \"surface area\" of the black hole is proportional to the amount of information \"inside\" the black hole. ( ",
"https://en.wikipedia.org/wiki/Holographic_principle",
" ) In other words, the \"amount of information on the surface\" is exactly the same as the \"amount of information inside\".",
"Another way to think of it is that someone outside the black hole might never see things go past the horizon, and when people talk about the 'surface' of the black hole they're talking about a region just outside the event horizon which contains everything that's ever \"fallen into\" the black hole, including the original star.",
"http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html",
"\n\"... So if you, watching from a safe distance, attempt to witness my fall into the hole, you'll see me fall more and more slowly as the light delay increases. You'll never see me actually get to the event horizon. My watch, to you, will tick more and more slowly, but will never reach the time that I see as I fall into the black hole. Notice that this is really an optical effect caused by the paths of the light rays.",
"This is also true for the dying star itself. If you attempt to witness the black hole's formation, you'll see the star collapse more and more slowly, never precisely reaching the Schwarzschild radius. ...\""
] |
[
"Can you (roughly) determine the dosage of a drug taken based off of the blood concentration?"
] |
[
false
] |
I do know there's no exact science for this because so many factors. Bioavailability, liver/kidney issues, weight, etc.. But say if an autopsy shows 0.33mcg/ml of blood for a certain substance.. Is there a way to reverse calculate what amount of the substance was taken? My best guess would be to get the persons weight and figure out how many L of blood they have and just multiply backwards. Again, I know there is no possible way to "accurately" determine how much was taken, but is there a rough way to guesstimate? Thank you EDIT - I want to thank everyone for their responses and overwhelming support. I really appreciate all of you. As I figured, it isnt as straightforward as I thought and there are so many factors in play here.
|
[
"In a criminal justice context, an expert toxicologist's opinion is often in the form of whether the concentration in the blood is \"consistent with a therapeutic range.\" ",
"So, for a given medication, there will be studies that say something like (just some random numbers here) \"this medication is usually dispensed in doses of 10mg once per day at the low end and 70mg once per day at the high end. People who take a 10mg dose typically have a blood concentration that peaks between X and 2X after approximately an hour, and people who take a 70mg dose typically have a blood concentration that peaks between 7X and 14X after an hour. The substance in the blood has a typical half-life of 8 to 12 hours. On a daily dose, baseline blood levels will stabilize at Y for 10mg daily and Z for 70mg daily.\" ",
"So, let's say someone has 80X in their blood. A toxicologist will be able to say with confidence \"that's not consistent with a therapeutic dose - this person ingested way more of the substance than a doctor would ever prescribe.\" So, either drug abuse or poisoning.",
"Now, say someone has 2X in their blood. A toxicologist can say \"that's consistent with a therapeutic dose\" - but not much more than that. It's quite possible that person took 10mg or 20mg an hour ago, and takes that every day - but they may have taken 70mg 16 to 24 hours ago as a one-off. Or they may have taken 40mg 12 hours ago, and every other day for the last month. Or they may have taken 1,000mg 48 hours ago. ",
"So, that's some of the nuance: it's fairly easy to ",
" certain dosage quantities/timelines, but it's much harder to say what actually did happen. A lot of the time, the first one's all that's needed."
] |
[
"Very good explanation. Thank you."
] |
[
"A single sample? No. Multiple samples? It depends. When dosed, the concentration in blood rises for a period and then declines as it is metabolized and cleared from the body. Each drug has a sort characteristic curve for the drug and it’s metabolites that you could compare to a series of samples taken over time which you may be able to use to determine the initial dose. It depends a bit on the dynamics of the drug clearance, and at what times you took the samples."
] |
[
"How can a single speaker make multiple notes at the same time that aren't on the same fundamental? (like a diminished chord, or a symphony"
] |
[
false
] | null |
[
"You're having trouble because you're confusing two different representations of sound. A speaker produces an arbitrary (within limits) pattern of air pressure versus time. A \"note\" is a particular pattern of air pressure versus time. We like to talk about \"pitch\" and \"timbre\" of a sound, and those qualities are the sensory equivalent of frequency.",
"From your question, I think you already know that a pure tone with a particular ",
" has a particular ",
" (like the famous A-440 or the less-famous, nonstandard, and far geekier C-512). ",
"I think you also know that most pitched sounds are actually created by combining multiple pure tones with frequencies that are integer multiples of a ",
", which is how we get the harmonic series and major chords. This is how different tones have ",
" -- the strength and (to a lesser extent) phase relationships between the separate pure tones in a complex tone combine to make the flavor we call ",
", and are what distinguish (for example) the verbal sounds for \"aaah\", \"eeeeh\", and \"ooooh\" sung at the same pitch: in normal aspiration, vocal chords produce a strong harmonic sequence. The relative amplitude of those overtones is set by weak resonances in your mouth and throat -- resonances that you change when you move your mouth parts around to form each vowel.",
"The combination of pure tones in your auditory system happens because of a fact of frequency decomposition of sounds (",
"): any repeating waveform can be represented as a sum of pure tones on the harmonic series above the fundamental (lowest) frequency at which the waveform repeats. This fact drove evolution of our ears: they carry out Fourier analysis (frequency/pitch decomposition) of incoming sounds, and tones with integer relationships are usually part of the same sound, so your ear groups such tones and gives you the sensation we call \"timbre\", as distinct from \"pitch\". You can fool that grouping system by making auditory puns, which is how and why chords work and are interesting to listen to.",
"So you're almost there. The deal is that most musical instruments are resonant systems -- they're designed to select particular frequencies from a source of non-pitched energy. The most obvious example is a flute, which resonates to select the fingered note from the broadband noise (a hiss) made by the flautist's breath across the hole in the lip plate. Brass and woodwinds use similar resonances with an interruptible air source (the lips functioning sort of like a reed in the case of trumpets and similar instruments), and strings resonate from broadband excitation by a plucking action or hammer strike. These sorts of instruments generally resonate at integer harmonics of the selected note, which produces overtones and gives their characteristic timbre. (A notable exception is the ocarina, which has bizarre non-integer overtones). ",
"But a (good) speaker is specifically designed to ",
" resonate at all -- an ideal speaker selects no tones at all, so if you feed it an electrical signal carrying white noise (like the white noise you feed to a flute), you'll get out a sound that represents exactly that white noise.",
"The \"multiple notes\" are just multiple frequencies that don't happen to have an integer harmonic relationship with any particular fundamental note (in human hearing range). If you sum two pure-tone signals into the speaker with a harmonic relationship of 3:2, they'll seem to merge to your ear to a single rich tone (a fifth interval). But if you sum two pure-tone signals into the speaker with a harmonic relationship of (say) 157:181, your ear will register them as two completely separate sounds."
] |
[
"consumers who just listen to music typically want speakers that color the signal to boost certain frequencies",
"In other words, (bad) speakers. :-)",
"Edit: I think you made a good point, sorry if my glib response helped trigger some downvotes."
] |
[
"But a (good) speaker is specifically designed to not resonate at all -- an ideal speaker selects no tones at all, so if you feed it an electrical signal carrying white noise (like the white noise you feed to a flute), you'll get out a sound that represents exactly that white noise.",
"That depends on who the end-user is. Producers and mixers definitely want speakers with these characteristics (but we call them studio monitors, not speakers), but consumers who just listen to music typically want speakers that color the signal to boost certain frequencies."
] |
[
"Why does a liquid having zero viscosity allow it to climb up and out of containers?"
] |
[
false
] | null |
[
"Great question! Even regular fluids can creep up the edges of a container a little thanks to capillary action. As you can see in ",
"this cartoon",
", if the surface attracts the liquid then gravity will be offset by these attractive forces a bit and the level of the liquid rises. If the surface repels the liquid, you get the opposite effect.",
"With a superfluid helium, you form a very thin (~30 nm) ",
"Rollin film",
" on the exposed surfaces of the container thanks to capillary forces. Gravity can then push the liquid up the walls some distance, or helium vapor might also just condense on the container surface to form the film directly (since there will also be some helium vapor coming off the liquid). Either way, eventually the Rollin film will connect the inside of the container to the outside in a continuous sheet. Then, like a hose used to syphon water, the film syphons the liquid helium out of the container."
] |
[
"Gravity pushes all fluids to the bottom of their containers. This puts pressure on the fluid which is relieved whenever a route is available. In zero viscosity fluids, that fluid pressure can be relieved because the attraction from the capillary effect can be stronger than gravity on an individual particle. Additionally, various flows can form depending on the shape of the container...",
"The capillary effect provides attraction sufficient for individual particles to overcome gravity (even in normal fluids), much like the way a siphon provides a flow route for viscous fluids ",
"You can think of the entire process as being something like a wick that expands in size to accommodate any flow."
] |
[
"It must overcome the force of gravity in order to climb up the wall. Where does that energy come from? If you let a superfluid climb up an arbitrarily high wall would you see its temperature decrease? "
] |
[
"Can photons be counted?"
] |
[
false
] |
Would it be possible to send out exactly 100 photons with different energies, and then measure exactly those 100 photons with the same energies at the receiving end? Or are photons just a unit/discretization of the EM field?
|
[
"Yes, we can detect single photons. The kinds of detectors we can use include things like ",
"single-photon avalanche diodes",
" or ",
"superconducting nanowire single-photon detectors",
". Such tools are not even that exotic and are routinely used in optics when you need to do photon-resolved measurements. Moreover, by combining such detectors with a dispersive element (e.g. grating or prism), you can get information about the energy of the photons you detect. The only important caveat is that the efficiency of these detectors are not quite 100%. So to take your example, if you put in 100 photons, you usually won't detect all of them (you might only count say 60 or 70 instead).",
"In any case, to sum it up: yes photons are definitely very much real and counting photons is both practical and often very useful."
] |
[
"It's worth pointing out that ",
"the rods in our eyes can actually detect single photons",
". Though, our eyes are set to only signal our brain if we get about 9 or so of them."
] |
[
"Though, our eyes are set to only signal our brain if we get about 9 or so of them.",
"Which is still low enough to get you random \"noise\" when it's dark, illustrating why firing for every single photon would be useless."
] |
[
"Do people in wheelchairs suffer from deep vein thrombosis more often than other people?"
] |
[
false
] | null |
[
"I'm at work and can't link any references right now. But, in short, yes. They are at a much higher risk of developing a clot in their lower extremities due to venous stasis. The blood in your veins isn't propelled by the pumping action of your heart - it is pulled towards the heart everytime you inhale or, in your legs, flex your calf. Someone in a wheelchair usually is not walking or moving their legs as much so that blood isn't able to cycle out as quickly. They may also be partially compressing their veins by sitting for long periods of time. This 'stasis' is a perfect environment for your body to create a thrombus. Wearing compression stockings lowers that risk, as well as physical therapy that moves and engages the muscles in the legs. "
] |
[
"Why do compression stockings lower the risk? "
] |
[
"It pushes the blood back up toward the heart. Essentially compression stockings are \"contracting\" because the muscles are not."
] |
[
"Is there an optimal ratio between iPod volume and car stereo volume in terms of sound quality when listening to an iPod in the car?"
] |
[
false
] |
I have noticed that different volume level ratios sound different to me in my car. I tend to turn up my iPod volume all the way up or close to max, and then just control the volume with my car volume knob. What is the science behind this? What would be the best strategy to take in order to improve sound quality?
|
[
"For the best quality, turn up your iPod until it starts to cause distortion. Then, go a little below that. This will give the stereo's input the highest dynamic range and a better SNR to work with. If you have some bizarre effects or non-additive noise, there could be problems, but generally, it is best to amplify signals as early down the chain as possible."
] |
[
"Assuming that you are using an AUX cable or a tape adapter (as opposed to a Bluetooth connection), put the iPod at quarter-to-mid-range, and control with car volume knob from there.",
"What's going on is that with the iPod volume set at max, you are losing some fidelity on the high end of the loudness (aka, your iPod is clipping), and so the sound is distorted before it reaches the car stereo."
] |
[
"No single component should be above 80%, generally speaking, that is when it starts flattening frequencies when increasing volume.",
"Disagreement usually starts coming in when there are people who know more about specific pieces of equipment. In this case, assuming that the iPod and Car Stereo are both fairly average when it comes to profiles. Someone who knows a lot about iPods, or your specific stereo system, might suggest balancing different."
] |
[
"Is there any difference between -1G, and being upside down?"
] |
[
false
] | null |
[
"It's not difficult to answer at all. I'm pretty sure lw421 is aware of the difference between zero net acceleration and -1G acceleration.",
"The answer is: No, there is no difference. An acceleration of -1G in the 'up' direction (i.e. the direction from your feet to your head) would feel the same as 1G in the 'down' direction (head to feet) i.e. being upside down."
] |
[
"You may be getting at one of the concepts of the ",
"Equivalence principle",
". Namely that the gravitational \"force\" as experienced locally while standing on a massive body (such as the Earth) is actually the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.",
"For example if you are sitting a train car and feeling 1G in a certain direction, there is no experiment you could do that would tell you whether the 1G acceleration is due to gravity or due to being in an accelerated frame of reference. You could be on the surface of earth or in a centrifuge in space, there is nothing about the force you are feeling that can be used to distinguish between these two cases."
] |
[
"This question is difficult to answer, because it is not very well defined. If you have a ",
" acceleration of -1g applied to you, you would fall \"up\", away from the Earth. If you found that you had something to stand on, say, a floor, the external forces on you would lead you to think that everything was normal, except that the world was upside down, and I don't think you would \"feel\" anything abnormal. If you instead had -1g of acceleration added to your normal 1g acceleration due to gravity you would find yourself floating and weightless."
] |
[
"If the Apollo program had continuousely failed, how much longer would it have taken the Russians to get a man to the moon?"
] |
[
false
] |
Let's assume the space race wouldn't have ended and NASA would have kept failing. Sorry I post this a 2nd time, but it didn't appear in the new queue for a few hours the last time and I don't think a lot of people saw it. I would be really interested in an answer and didn't find anything.
|
[
"About 20 hours before we landed on the moon the russians had launched and landed an unmanned space vehicle on the moon. Don't think it was able to return to earth... they just wanted the title of landing something safely on the moon before we did.",
"I would guess that if there were still that race to do it and we kept showing promise that it would happen soon(to motivate them) that they would have landed on the moon within 18 months.",
"This is complete speculation but the cold war was essentially the race to the moon, the cuban missile crisis, and the Miracle on ice in lake placid.",
"Edit: Research shows i was wrong... Sorry. ",
"\"In a race to reach the Moon and return to Earth, the parallel missions of Luna 15 and Apollo 11 were, in many ways, the culmination of the space race between the space programs of both the United States and the Soviet Union in the 1960s. The simultaneous missions became one of the first instances of Soviet/American space cooperation as the USSR released Luna 15's flight plan to ensure it would not collide with Apollo 11, though its exact mission was unknown.\"",
"http://en.wikipedia.org/wiki/Luna_15"
] |
[
"Don't think it was able to return to earth... they just wanted the title of landing something safely on the moon before we did.",
"That wasn't the first successful landing on the moon though. The first successful soft landing is ",
"Luna 9",
" in 1966, three years before. The US then later launched ",
"Surveyor 1",
" which was also well before the landing of people. "
] |
[
"http://www.fas.org/spp/eprint/lindroos_moon1.htm",
"TLDR: They were not that far behind, but Korolyov died prematurely and they had a series of failures due to political dumbassery.",
"You could have just googled \"soviet moon landing\"."
] |
[
"What would I see with the naked eye if I was half-way to Andromeda?"
] |
[
false
] |
So I know that today's astronomy photos aren't like regular photographs: they have long exposure times and the colors aren't exposed the same way the eye would see them. So I'm wondering if the human eye would ever be able to see anything like what the hubble telescope saw when it took the photo. If I was in a completely dark spaceship half way between the Milky Way and Andromeda, would I be far enough away from interfering light sources to look out the window and see an array of galaxies with my own eyes? What would I see?
|
[
"It would look twice as big and four times as bright. So what does that mean? Believe it or not, the angular width of the Andromeda Galaxy (from here) is about 2 degrees. That's four times the apparent size of the Sun or Moon. The reason why we can barely see it is because it's so dim. It's got an apparent magnitude of 3.44 which is about as bright as the dimmest star you can see in a suburban setting. Four times brighter is about magnitude 2 (the magnitude system is weird). That's about as bright as a fairly bright star.",
"To be as bright as the Moon, you'd need to be about 95% of the way there. At this distance it would have an angular width of 40 degrees. That's most of your field of view. So that's where you want to go to get a nice view."
] |
[
"Well first - the colors in the photo depend on the frequencies taken and any post processing done. Lots of the photos are indeed in the visual range and generally minimally processed - so they do represent the real colors. Obviously IR, UV, Xray, etc... are false colored (as are specific filtered photos, such as hydrogen filtering, etc).",
"Now second - what you would see depends mostly on the local conditions. One big factor is dust. Space is a very very dusty place. If you were in a relatively dust free area, then your view should be pretty nice.",
"However, you would not see the deep field photo such as the example you gave, with the naked eye (those are pretty long exposures to capture that detail). But you would probably have a pretty impressive view of the Milky Way and Andromeda.",
"As for exposure times - yes... to make the photos many many pictures are taken and combined - and each picture may have exposure times from minutes to hours in length (depending on the object and the particular instrument being used, etc)."
] |
[
"The problem with dust is that even if you are in a fairly dust free area - the closer you get to the galaxies the duster it gets (therefore, you are looking through dust at the galaxies).",
"You might see galaxies besides the two big ones - depending on their locations etc - You won't see the deep field because it is still too dim and the distances too vast for your eyes to get useful detail.",
"Even the closest galaxies will still not be these huge expanses - but simply bigger and brighter than you see them now (and certainly, with much more detail).",
"The problem here is that distances in space are so very very big.",
"However, do keep in mind that you ",
"can see other galaxies from earth, with the naked eye",
" - you just don't perceive them as such (again, dust, distance, obscure the structure so you end up with fuzziness and loss of detail)"
] |
[
"Is the size of DNA proportional to the complexity of the organism?"
] |
[
false
] | null |
[
"Generally, no",
".",
"This observation was originally referred to as the \"C value paradox\", as people thought it didn't make sense that there was no relationship between DNA content and perceived organismal complexity. The resolution comes chiefly from the fact that most DNA in most genomes (and especially the large ones) does not actually code for genes, and so simple measures of genome size are not in any way measures of the amount of \"information\" present in the genome.",
"People now sometimes refer to the \"C value enigma\", which refers to a subsequent set of questions about why there is so much variation in the amount non-coding DNA present in eukaryotic genomes."
] |
[
"It's also not easy to rank organisms by complexity. Which is more complicated, you or a crayfish? You're physically bigger and you have a big brain and all, but your life cycle is really basic and you only have four limbs.",
"You can try ranking number of coding genes but a few chunks of the noncoding regions have functions too, like regulating genes. "
] |
[
"It's also not easy to rank organisms by complexity",
"Exactly, thus my careful choice of the word \"perceived\" complexity."
] |
[
"How long will the astronaut's footprints on the moon really last?"
] |
[
false
] |
We've all heard the footprints on the moon will last many millions of years, until they're eroded by micrometeorite collisions, or moonquakes, or the like. But I once read a suggestion that the constant monthly cycling of the lunar regiolith from daylight to darkness, from hot to cold might make them disappear far faster, due to the expansion and contraction of the particles in the dust. Has anyone else heard of this? How long will man's footprints on the lunar dust really last?
|
[
"This question is probably worth a what-if.xkcd.com, but I'll give it a Fermi estimate shot (Ignoring anyhting about regolith moving, because I have no idea about it and it feels \"wrong\" to assume the effect is large...): I'd say the biggest chance of disturbing a footprint is via shaking due to a nearby asteroid impact. Sadly the impact rate on the moon is very difficult to determine from earth, but, assuming we can extrapolate from earth with it's 33 metric tons per day (",
"http://www.nasa.gov/centers/marshall/news/lunar/program_overview.html#link4",
") for a surface of roughly 500000000 km2 as compared to the moon with roughly 0.075 of it. Most of those 2.5 metric tons are probably impacting around the plane of the ecliptic and about (just guessing here) 1kg in mass, so 2500 impacts over 25000000 km2 (assuming that is the area hit most frequently, which thankfully is also where the footprints are) makes roughly one impact per day per per 10000km2. Such impacts have enough energy to affect an area of, let's say, a 1m2, meaning any such should be impacted, on average, about every 10000000000 days, or roughly every 30000 years. So that is the scale of the lifetime I'd expect... I hope some real expert can jump in, but I feel the number sounds about right ;-)"
] |
[
"Let's postulate using snow as an example. Not accounting for melt, let's assume the temperature remains constantly cool. ",
"Footprints generally expand in snow first and for quite a while as the geological motions and rays of light apply very small amounts of energy. This is similar to the slow geological motions you describe. ",
"Footprints in snow would be present for years. With the moon you don't get nearly the same activity as conditions arnt the same as earth. So I would hypothesize they'd be there for many centuries until an outside body, man or objects, disturb the surface again"
] |
[
"Yeah, I was likening the forces of the moon acting neutral to the footprints, as I made the bit tortured correlation between footprints on earth versus footprints on the moon. I suspect it would be far less amplified (sun rays reflecting equally across the surface of snow is somewhat different to electrostatic levitation) which is why I'd postulate at centuries. ",
"I know there are reports of frozen footprints in the Himalayas, which some speculate have contributed to yeti footprint sightings. In those cases almost 150years later some footprints have enlarged but are still definitively footprints. ",
"So I'd suspect the moon's surface forces have a neutral effect: enlarging the prints slowly over time as particles fall from the highest points to rest at the lower points. Considering the lack of external forces I would make the educated guess that it would be exponentially longer than we can actually witness here on earth"
] |
[
"How do viruses cause illness?"
] |
[
false
] |
[deleted]
|
[
"Viruses exist in a weird biotic space between living and non-living. That is, they do a lot of the things that living things can do, but there are a couple things they cannot do. Most notably, a virus cannot create other viruses. Instead they rely on the machinery of a host cell to make viruses using their viral genetic information.",
"The advantage to doing this, is that viruses can be very small and do not require their own energy supply, which is a very efficient way of existing. The catch is they have to be pretty specific to the host. They can't just infect the first cell they come across, they have to find cells that have specific receptors on them that match closely with tags on the virus.",
"It's really hard to comment on hypothetical aliens because there isn't a lot of consensus about what they will be like, but it's unlikely that they will have cells that closely resemble ours on the molecular level, so any virus that was well-adapted to a particular alien host cell would be unlikely to also match to a human cell.",
"The more interesting thing would be if the alien viral niche were filled in some completely new way that didn't involve receptors or protein tags. I have no idea what that would be, but any biotic being that arises suddenly (like say by crash-landing in a UFO) with a completely new way of doing something (like say usurping a host's physical machinery and energy supply to reproduce) might have a chance of becoming invasive, since there would not be an evolutionarily tuned resistance in our population."
] |
[
"Right, so it is sorta how it popped up in my head, it's possible to be pandemic due to the lack of resistance, like diseases in our own past, but also possible to be ineffective, due to it's own evolution following a path that is two dissimilar to even allow infection. "
] |
[
"Yes, similar to introducing a species into a novel environment. It might not survive, or it might survive too well and take over everything else.",
"I'm inclined to say that it's less likely to take over given the huge adaptive disadvantage, but I'm sure there's someone out there who knows way more than me and would have a different opinion."
] |
[
"How \"mobile\" are bacteria and viruses on dry skin?"
] |
[
false
] |
It's flu and cold season so I'm curious about a few related things. Assuming dry hands and dry door knob or similar surface: How easy is it to transfer bacteria/viruses from the surface to your palm/front of your fingers? If you touched the surface with the back of your hand, can the germs easily make it around to your palm and front of your fingers (where they are more likely to get into your mouth/nose)? My rationale for the second question is really wondering whether opening a public door with some other part of the hand/arm can help prevent illness. Thanks!
|
[
"Someone correct me if I'm wrong, but I think that bacteria/viruses spread easier when there is some \"wetness\" involved. It's why if you drop some dry food on the ground, the 5-second rule is o.k., but if the food or ground it lands on is wet, you shouldn't eat it at all.",
"You won't feel the flu symptoms immediately when you have it, so the doorknob may already have the influenza virus. The flu is spread by a cough or sneezes. People can sometimes sneeze into their hands (ew), then touch things that you touch. So it wouldn't be super rare to have some trace on the doorknob, but I wouldn't say it is common. ",
"Regarding the second question, I'm not too sure. Although you ARE more likely to touch your face with the palm side of your hand than say your elbow. ",
"Not too educated in this field, but I tried. :)"
] |
[
"The 5 second rule isn't science, its just an excuse people give so they are not wasting food. The vast majority of dirt, bacteria etc will transfer to the dropped object instantly. That being said you are very unlikely to get sick just from eating dropped food unless you dropped it on a rotting carcass or something."
] |
[
"Skin-object contact transfers potential pathogens pretty easily, in both directions, even if your skin feels dry. However, there's negligible \"traveling\" across the skin, so yes, using your elbow or similar to open a door instead of your hand is generally a pretty good practice re: preventing exposing yourself to pathogens you pick up by contact with surfaces in the environment. "
] |
[
"How come when you have been wearing a hat/sleeping/etc. your hair gets stuck in a postion making \"bed-head\" or \"hat-hair\", and stays like that until it is made wet. Why does water fix it, what effect does water have on hair? Why can't you put the hair back into place without water?"
] |
[
false
] | null |
[
"It is to do with Hydrogen bonding / the heat generated by close currents of heat between the hat and your head. Your hair is made of keratin and that keratin protein contains amino acids (mainly cysteine for disulphide bonds creating ''hard'' keratin strength), hydrogen bonds and side chain linkages. Proteins under heating, for example via extreme measures (straightening hair straighteners) cause the hair to permanently take a shape. Because you aren't going to be generally breaking the strong disulphide or salt bonds, when you use heat the energy breaks hydrogen bonding which is most abundant in hair. It gives hat hair, which is fairly clay like and easy to form. It makes sense that water ''resets'' it because water will allow reformation of hydrogen bonds in hair by drying and cooling. Hope this helps."
] |
[
"Thats actually really cool!!! Thanks!"
] |
[
"No problem. Me and my friend were curious the other day so I had decided to discover the properties of Keratin so this is clearly close to my heart."
] |
[
"How can someone become more intelligent?"
] |
[
true
] |
[deleted]
|
[
"You need to be very specific about what you mean. Intelligence can be broken up into a lot of different faculties."
] |
[
"You need to be very specific about what you mean. Intelligence can be broken up into a lot of different faculties."
] |
[
"This is an extremely topical question. Briefly, we believe there is a neurobiological substrate for fluid intelligence. If that is definitively true, there may be methods which may improve fluid intelligence by targeting that neurobiological substrate - either by training, or by other intervention.",
"For example, ",
"recent studies have shown some promise with some forms of training to improve measures of fluid intelligence",
". Even these studies don't tell us what the right approach should be, even if there was one. Most critically, behavioral techniques (e.g. training) are subject to all sorts of psychological impacts, as one example, ",
"the type of flyer used to recruit people may influence the gains observed",
".",
"However, with the long view, there's many things that are related to fluid intelligence, like diet, exercise, socioeconomic status, education level, etc. Some of these things are biological in nature (e.g. exercise) and others are more cultural (SES). Improving ones \"intelligence\" then can probably come about through improving factors that support intelligence, as well as looking towards \"brain-based\" solutions to improve intelligence.",
"As with anything, this is an area of serious investigation, and some serious research funding has been recently sunk into this topic - so expect more information over the coming few years."
] |
[
"Are solar panels as effective on mars, further from the sun, and with less atmosphere?"
] |
[
false
] | null |
[
"If the question is, would the same panel produce less power on mars than on the earth on a clear day (assuming for a minute that both measurements are made at on the equinox at nooon and on the equator), then the answer is yes. While its true that on earth we lose some solar irradiance to absorption in the atmosphere, the amount mars loses to distance is more important, because the brighness of a point source falls ",
"by the inverse of the distance squared",
". Think about the light expanding as a spherical shell, whose area is increasing by r",
" but which always contains the same amount of total brightness.",
"The solar irradiance just outside our atmosphere is around 1360 W/m",
" Mars is 1.5 times farther away from the sun, so it would get around 1360/1.5",
" = 600 W/m2. On the other hand on a clear sunny day, even with the atmosphere's attenuation, the solar irradiance on earth can be greater than 1000 W/m2 (1000 being the \"standard\" irradiance used when specifying the power a solar panel makes)",
"On the other hand, the panel on mars would use those 600 W/m2 more efficiently, because it would be colder"
] |
[
"On the other hand, Mars has a completely different climate with far fewer snowstorms, so while under optimal conditions solar panels on or near Earth will be more effective, under average conditions, panels on the surface of Mars may be comparable or even more effective."
] |
[
"thank you"
] |
[
"If you live an incredibly healthy lifestyle but smoke cigarettes, are they as bad for you as they would be for an un-healthy person smoking?"
] |
[
false
] | null |
[
"Many studies have controlled for other lifestyle choices. Smoking is very bad for your health, and most of the really bad stuff happens between age 60 and age 70. Obesity is not a risk factor for lung cancer, for example. But for coronary heart disease, both smoking and obesity are risk factors, and perhaps smoking more so than obesity! ",
"http://www.nejm.org/doi/pdf/10.1056/NEJM199003293221303",
"\n(See upper left graph in figure 2) "
] |
[
"It's a little like buying a lottery ticket. Any given lottery ticket might just be the one that wins the jackpot, but the chance of a single lottery ticket winning is extremely tiny. However, you could theoretically buy a single lottery ticket, a single time, and win. You could also buy 1,000 tickets a day and never win. Statistically though, your chances of winning are much, much better if you're buying 1,000/day.",
"Except instead of winning the lottery, you get cancer. "
] |
[
"Today on \"Hey Kids, Try Some Cigarettes:\" If you're under 35 years of age, quit before you're 35 and you'll have negligible long-term effects. 35 to 45 is almost as good, after 45 it gets a bit dicey.",
"Source? THE NEW ENGLAND JOURNAL OF MEDICINE\n",
"http://www.nejm.org/doi/full/10.1056/NEJMsa1211128"
] |
[
"Are these lights safe to use?"
] |
[
false
] |
I'm interested in induction lighting because of the wattage/great benefits for my green house during the winter months. I showed my garden buddy/neighbour and preached about them. The next day he said that they create a bunch of radiation, and the electro magnetic field they give off is bad for you? I could grow all year with these and get a mega head start for spring. I also don't want to expose myself to radiation at high levels or electro magnetic wubb-wubbs. How bad are these? I'm think in five years I could have as many as six? Thanks!
|
[
"It's safe. The most you have to worry about is interference for your radios, which shouldn't happen with newer lamps. ",
"The radiation they emit is radio waves. It's perfectly safe. "
] |
[
"http://imgur.com/dNqrjlS",
"electromagnetic radiation is just a fancy word for light.",
"the kind of radiation that gives you cancer is the high energy sort. short wavelength, high frequency, high enough energy to knock off parts of your DNA and other dangerous stuff.",
"microwaves are lower energy than visible light, but are a bit unique in that they interact very specifically with water, causing it to heat up. so those are a little dangerous because they can burn you, but you would notice.",
"How bad are these?",
"according to I_Cant_Logoff, they are emitting electromagnet radiation in the same part of the spectrum as radios. so normal, household lightbulbs are closer to x rays and fukushima than these lamps."
] |
[
"Awesome! Thank you!"
] |
[
"Why do individual particles have different concentration gradients?"
] |
[
false
] |
I'm learning about diffusion in HS biology, and my teacher said that due to the random kinetic energy of particles they will go down their concentration gradient to areas of lower concentration. This makes sense to me. He then went on to say that concentration gradients are individual to different particles, and Co2 and O2 will go down their individual concentration gradients rather than higher concentration of solutes in general would flow towards an area(s) of lower total solute concentration. Why is this? Thanks!
|
[
"Diffusion of molecular fluids is caused by Brownian motion, i.e. the nearly random motion that results from multiple collisions between particles at atomic scales. It is a process 'powered' by entropy. Diffusion does not happen because the different molecules strongly repel each other. As such, the density individual constituents will matter - molecules will move against their concentration gradients. Furthermore, diffusion takes place at different rates for molecules with different masses and sizes (i.e. the diffusion coefficient is a function of the solute's mass and its overall 'shape').",
"You can think of what's happening using the following thought experiment; imagine you have a dilute solution of two solutes which have the same diffusivity and which one is 'blue' and the other one is 'red'. The overall volume is kept constant, the amount of each solute the same as well and they have the same temperature. We begin with the two solutions in two compartments separated by a barrier; then at some time we begin the experiment by removing the barrier. The two solutes will begin to mix due to diffusion, until, after some time, we will have a macroscopically homogeneous 'purple' fluid. Clearly, the end state is different from what we began with, but if we look at the ",
" of the densities at the initial state and the final state it can be seen that there is no change. Therefore, the model considering only the sum of the densities cannot portray the dynamics accurately.",
"Another way to put it is that mathematically, the diffusion equation corresponding to Fick's second law is linear, so that solutions to the equation for the density of each component of the mixture are also solutions for the mixture (given by the sum of the densities).",
"That said, this model is valid only for relatively dilute solutions where the interaction between the solutes is negligible. If one component needs to displace another component due to crowding then a model that takes account of this effect would be called for."
] |
[
"So my understanding of what you said is that because molecules don't \"push off of each-other\" as my teacher put it (which led me to believe that more molecules to push off of led to diffusion away from that area), the only reason they diffuse is their random motion, which I see would randomly distribute particles evenly over time. ",
"Moreover, difference in diffusion rates means that different particles will diffuse in different ways, hence they have their own gradients. ",
"So the gradient is simply a representation of the statistical tendency for particles to spread out? Did I get this right? "
] |
[
"Yes this is true. The particles do collide and scatter at atomic scales and several collisions result into a motion for each particle that appears random. Given that the molecules will not react with each other, they do not feel their density over large scales. The large-scale distribution in space and its dynamics emerge from the molecular motions."
] |
[
"What would be the best method for us to use if we wanted to send and receive information across vast interstellar distances?"
] |
[
false
] |
Is it possible to create, say, a radio wave laser? How far could such a laser reach though space? I've heard that even lasers do spread out a bit. Would a radio wave laser be our best option for interstellar communication, or would it be better to transmit with something like the I heard from that it would be possible for the Arecibo Observatory to communicate with another similar-sized dish located half the distance to our galactic center. That's pretty far. Is that really true? (Of course, it would take a very long time.) How focused of a beam can this thing make? Would a laser reach farther?
|
[
"Remember what subreddit you are in! That is science fiction. Besides, if I wanted a solution from science fiction, I'd have gone with the ",
"ansible."
] |
[
"Remember what subreddit you are in! That is science fiction. Besides, if I wanted a solution from science fiction, I'd have gone with the ",
"ansible."
] |
[
"I don't know about the 'maser' wonderfuldog mentioned, so it's worth looking into that. I also don't know about this talk on Cosmos about the Arecibo Observatory. Last time I checked, there really wasn't any feasible way to transmit data over interstellar distances - the power required to overcome the inverse-square law when it comes to communicating to other star systems with current technology is absolutely mind-boggling, and practically insurmountable. Probably we would have to rely on good old space-ship communication; much slower than the speed of light.",
"That being said, it's been a few years since I've looked to see how things are going, so there could be something with that observatory or some other new technology. But my 'hunch' is that neither option is too realistic (so considering this is askscience, feel free to ignore that hunch as it should be ignored).",
"A laser would not reach too far. My post ",
"here",
" details an estimate of the strength of a standard laser reaching Mars. The area of the laser, which would start off at a few square millimeters, expands to 1.3 x 10",
" square kilometers by the time it reaches Mars, something extremely close relatively speaking. By the time this laser reached even the closest star at 4.2 light years distance, the beam would have expanded to be about 79 billion kilometers across. This would give a beam 'area' of about 2 x 10",
" square kilometers - or enough that you would get (roughly) 1 photon from the original laser occupying every million square kilometers of the final laser beam at this star, per second. That's already so far beyond un-detectable that it's silly, and that's just the closest star.",
"Specialized lasers could of course greatly improve power outage and cut down on this expansion rate quite a lot - but unless technology is improved tremendously, the inverse square law will still overpower any linear increase in laser technology quite fast."
] |
[
"Are there more \"demons\" in physics than Maxwell's and Laplace's?"
] |
[
false
] | null |
[
"I'm not aware of any other \"demons\" in physics, so in the following I'll sway away from your question a bit to at least try to get a list started of things in the same ballpark. There is ",
"Descartes' Demon",
", ",
"Morton's Demon",
", the ",
"Utility Monster",
", ",
"Newcomb's Predictor",
", ",
"Swampman",
", ",
"Zombies",
", and the Experimenter in the ",
"Sleeping Beauty Problem",
" in philosophy. In physics there are ",
"Maxwell's Zombies",
", the ",
"Matrioshka Brain",
", ",
"Boltzmann Brains",
", of course ",
"Schrodinger's Cat",
" and ",
"Wigner's Friend",
", and the potentially superpowerful simulating A.I. during a ",
"Big Crunch",
". In A.I. there is the superpowerful AI in ",
"Roko's Basilisk",
". "
] |
[
"In this respect, merely knowing about the Basilisk — e.g., reading this article — opens you up to hypothetical punishment from the hypothetical superintelligence.",
"Geez thanks."
] |
[
"It's a thought experiment to see if the second law of thermodynamics could actually be violated. It's purpose wasn't to find a mechanism that changes the temperature of two chambers."
] |
[
"If we had bred domesticated cats the way we did dogs would we have large house cats (size of great danes) and mini cats (size of chihuahua)"
] |
[
false
] |
From what I understand cats were never selectively bred in the same way dogs were.
|
[
"Yes, dog breeding is not that ancient and the changes we see today have been achieved in a shot time span.They do it with cows and other animals we use, it would work with cats too."
] |
[
"there is a large house cat you can get called a shavana cat i think it costs £12,000 its a normal cat crossed with a african wild cat bout the size f a medium dog an plays fetch."
] |
[
"We would definitely have a wider range of cats if we focused more on selective breeding. ",
"However, I remember hearing somewhere (believe it was a Ngeog in the womb show) that dogs have a particular gene(or just disposition) to huge rapid changes in their physiology making them the perfect candidate for accelerated selective breeding.",
"So while its possible to achieve the variety with cats, I believe (speculation) that it would involve a much longer span of time than with dogs."
] |
[
"Was the \"seasonal flu\" a phenomenon before the 1918 Flu Pandemic?"
] |
[
false
] |
I was reading that casually dropped this paragraph: If we are lucky, year over year, SARS-CoV-2 will evolve to cause milder disease than it has these past two years. That would be consistent with the virus that spread in 1918, which became the seasonal flu. It never again produced the same level of mortality as it did during its first two years, but the virus continues to evolve and kill hundreds of thousands of people every year. Most of us have come to accept this as inevitable. Were seasonal flus not a thing prior to 1918? Did urban dwellers and other people in 1910, 1850, 1600 not head into winter half-expecting to catch the flu?
|
[
"The 1918 flu was the origin of one strain of seasonal flu, but others are older. The word \"influenza\" itself comes from an Italian phrase \"influenza di freddo\" which bascially means \"influence of cold\" which goes back to the 1300's. As the name indicates, it was associated with cold weather even then. It may have been described even earlier by Hippocrates, but it's hard to say if that was really the flu as we know it. After all, ",
" respiratory diseases are associated with cold weather and cause similar diseases. There were some similar (but less intense) flu epidemics documented back to the late 1800's.",
"Article on the topic: \n ",
"https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(19)30148-5/fulltext",
"Still, influenza is a pretty fast moving disease. We can get some idea how old individual strains are using molecular clocks. I'm used to reading about these dating animal lineages, when the timespans are in the hundreds of thousands or millions of years. With flu, we are talking about timespans of decades. All three currently circulating influenza A strains first appear in the 20th century, and the deepest branches showing up on the tree in the linked paper only go back to the 1800's! That doesn't mean ",
" wasn't around before then, just that each gene they looked at came from a common ancestor at about that time.",
"https://www.pnas.org/content/106/28/11709",
"Divergence times ",
" strains are all over the map. Influenza A and B have been estimated to have diverged a few thousand years ago, a few hundred years ago, or even about a hundred years ago, but I couldn't find a really recent paper. Here's a couple the first promoting a long timespan and the second a short one.",
"https://academic.oup.com/mbe/article/19/4/501/995507",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2443812/"
] |
[
"You're misreading that section as saying that seasonal flu didn't exist before 1918. What it's actually saying is that the 1918 flu became the seasonal flu, by ",
" the seasonal influenza virus(es) that were circulating at the time. All the seasonal influenzas we are now (2021) infected with are direct descendants of the 1918 virus. See ",
"How did the Spanish flu pandemic end?",
" for more detail.",
"Before 1918, influenza was well known (although probably often confused with other diseases - the cause of influenza wasn't identified until 1934), and it was well known to be mainly a winter disease. This was muddled by pandemic influenzas, which often spread outside the normal season, but in general influenza was known to be a winter disease. For example, if you look at Table 9 (\"DEATHS (EXCLUSIVE OF STILLBIRTHS), FROM CERTAIN CAUSES, BY MONTHS, FOR THE REGISTRATION AREA, REGISTRATION STATES, AND CITIES OF 250,000 POPULATION OR OVER IN 1910\") from the ",
"US Mortality Statistics from 1910",
" you can see that in Philadelphia in 1910, 150 of the 159 influenza deaths occurred between November and April, with none in July or August. ",
"This was so well known that some textbooks warned that it was far too easy to simply ascribe ",
" winter death or disease to influenza. Little pamphlets about family health explained that influenza season was closed-window season, and he prevention for influenza was to open windows."
] |
[
"Flu was a thing before 1918, but in 1918 there was a new strain of H1N1 which most people had no immunity to (was zoonotic and had just crossed from birds to humans). If I remember correctly some old people did as they was a similar virus like 30 years earlier. Hence part of the reason the death rate was lower in the elderly"
] |
[
"Is there any validity to the claim that humans are capable of absorbing adrenaline from animal meat?"
] |
[
false
] | null |
[
"Firstly animals are undoubtedly stressed when they are slaughtered or during the build up and as such will release hormones such as adrenaline into their bloodstream. Secondly the idea that it would disrupt our own adrenaline balance is because adrenaline does not have a negative feedback mechanism and so the addition of adrenaline won't inhibit production of our own. Lastly ",
"this",
" study didn't see any significant deviation from normal adrenaline levels, there is also plenty of anecdotal evidence that suggests no impact of any significance is noticed through eating meat.",
"Edit (because it no doubt will pop-up): Adrenaline = Epinephrine "
] |
[
"Correct, adrenaline is the molecule ",
" 9 ",
" 13 ",
" 3 . It has a few different molecular configurations, but all are treated by the body identically, and the molecule is the same in all animals that possess it."
] |
[
"Dumb question, ",
"Adrenaline is adrenaline right? I mean it's just a molecule, there isn't a difference between human and animal adrenaline?"
] |
[
"Why is having an extra chromosome bad?"
] |
[
false
] |
Why does having an extra chromosome lead to Down's syndrome and not provide additional genetic instructions that are beneficial or at least benign?
|
[
"There actually are some benefits to having an extra chromosome. For example, individuals with Down's Syndrome have a much lower risk of many types of cancer:",
"http://www.nature.com/nature/journal/v459/n7250/abs/nature08062.html",
"Obviously the benefits are vastly outweighed by the other problems suffered by individuals with the disorder. It might be handy to think about cancer (in non-Down's Syndrome individuals) to get a feel for why an additional copy of a chromosome is usually detrimental since cancer is the classic situation where cells aren't functioning properly. Many cancer cells don't have a normal diploid genome with two copies of each chromosome. Some have entire extra copies of chromosomes. Some have extra copies of just part of a chromosome (so say an extra half of chromosome 1 floating around). ",
"In normal cells, the cellular machinery keeps the activity of each of your genes highly regulated. If your genes are more or less active than normal, then bad things like cancer can happen. For example, there are many genes that regulate cell death and make sure damaged or mutated cells are killed. If those genes are turned off then the mutated cells can survive when they shouldn't. On the other hand, many genes control how fast cells grow and divide. If those genes are way more active than normal then your cells may grow out of control and form a tumor. ",
"Let's go back to the extra chromosome concept. Instead of two copies of each gene, you now have three. If all those copies are active, you've got a 50% increase. And we already know that increased activity of some genes can cause cancer. So if you can see how having an extra copy of a gene might increase your chances of getting cancer. It's important to note that not all genes will have that effect. But there are a lot of genes on each chromosome. Chromosome 21, the chromosome involved in Down's Syndrome, has ~500 genes on it. Our largest chromosome has ~4000. Each of those is a chance for something bad to happen when you end up with another copy. That \"something bad\" might be cancer. In Down's Syndrome it ends up being mental retardation and other issues."
] |
[
"I think the exact mechanism of this is largely still a mystery but a group of researchers have found that an extra chromosome has an impact on the localisation of DNA within the cell which leads to changes in the normal gene expression profile and messes up the equilibrium.",
"Here's",
" the reference to the study if you want to read it.",
"Edit: it seems I misread the study a little, the extra chromosome in the study leads to modification of the chromatin environment and therefore changing the whole transcriptome, not by changing DNA localisation. I mistakenly associated changes in the nuclear compartment mentioned in the abstract as changes in DNA localisation."
] |
[
"As you know, Down's Syndrome is caused by an extra copy of chromosome 21 in humans (three copies, rather than the usual two).",
"Down's Syndrome phenotypes (characteristics) have long been thought to be caused by gene overdosage - i.e. the 50% increase in expression at the RNA level of trisomic genes [",
"Nikolaienko, 2005, Gene",
"]. The minimal interval associated with \"classic\" Downs Syndrome contains 33 genes [",
"Olson, 2007, Human Molecular Genetics",
"]. ",
"Researchers studying a pair of monozygotic twins where one was trisomic (Down Syndrome) and the other was not, found that 337 gene-expression-discordant chromosomal regions across the whole genome [",
"here",
"], suggesting that not only does the 50% overdosage for those 33 genes have a biological impact directly, but those genes can also impact gene expression in other areas (6/33 are transcription factors that work to activate or suppress the activity of other genes), and the entire chromatin appears to be remodeled in order to accommodate the extra DNA (specifically H3K epigenetic methylation marks) [",
"Letourneau, 2014, Nature",
"]."
] |
[
"Why is time a physical aspect of the universe, instead of only space?"
] |
[
false
] | null |
[
"It has to do with the fact that the gravitational field has to be \"divergence free\" in empty space. What this means is that in the spaces between matter, the field has to \"spread out\" in such a way that there are no sources or sinks of gravity. The number of dimensions there are in space determine exactly how the field has to spread out, and - very roughly speaking - if there are more dimensions there is more \"room\" that has to be spread into. The results is that gravitational orbits, which correspond to clumps of matter interacting over empty space, are dramatically different when there are more (or less) spatial dimensions."
] |
[
"There isn't really a why. It's just something we observe about the universe. Asking that is similar to asking why we can move in 3 directions spatially instead of 2, 4 or any other number."
] |
[
"If there existed a 4th dimension, what would it look like?"
] |
[
"If the human body's response to infection is a fever because heat kills the pathogens, Aren't we delaying the healing process with fever reducing drugs?"
] |
[
false
] | null |
[
"As a general rule in health care, we don't give fever reducing medications unless a fever is above 101.5 just for that reason. The heat does indeed kill the pathogens, but on the flip side, we must closely monitor to make sure the fever does not become high enough to cause damage to the body in the process. ",
"Source: I'm a nurse. "
] |
[
"Fevers do indeed kill the pathogens (somewhat) but fevers also serve the purpose of speeding up the chemical/metabolic processes in your body that are killing the pathogen and helping you heal. ",
"We run into trouble when the fever starts getting so high that these processes are actually negatively affected, and proteins (namely enzymes) in your body begin denaturing and/or not working as efficiently as they could be. ",
"This is why you often hear of doctors prescribing fever reducers to \"control\" the fever. They don't want the fever to get so high that it is actually harming you, but they don't want to wipe the fever out completely, either. "
] |
[
"This is for the most part true, but I would like to expand upon your statement.",
"In actuality, fevers are likely mismanaged in most hospital settings. Though I am sure that there are exceptions, fevers will not cause bodily harm until a temp of 107.6 Fahrenheit is reached (at which point brain damage may result). In most hospitals, doctors provide antipyretics like acetaminophen to patients for \"comfort care\". Whether or not this is a good or bad thing is debatable. If one were to ask a patient how they felt at a temperature of 101, this patient more than likely will respond that he feels fine. However, many doctors will give him some Tylenol just to drop that temp a little bit, in the name of comfort. If the patient had complained of discomfort then the medication would seem very reasonable, but with no complaint, should it have been given? ",
"The answer is that we don't really know for sure. Yes, the fever is beneficial in general, but it is likely not beneficial enough to significantly affect length of illness duration or hospital stay.",
"However, one very direct affect is that of cost - the average dose of acetaminophen in the hospital costs about 11$. This may seem like a small amount, but it adds up to a whole lot over the course of many patients and many doses. ",
"Source: I am a fourth year med student, but this information is from an Infectious disease specialist for over 30 years with whom I am currently working. In his opinion we need to drastically cut down on use of antipyretics, but I myself am still uncertain (but leaning in his direction). "
] |
[
"In places on the earth where the sun never rises at some times of the year, do plants that live there die as they cannot perform photosynthesis?"
] |
[
false
] | null |
[
"All plants dont always need photosynthesis to live. All plants can consume oxygen the same way humans and animals do. The same way plants dont die during the night :)",
"But to answer your question -> no plants dont die, we do have less plant life in general and fewer divers species of plants because of this"
] |
[
"Also, the places you mention have no sun in the winter, and there are a lot of places where plants go dormant in the winter, so the lack of sunshine isn't as critical as you might think."
] |
[
"I live where that are many maples and conifers.\nMost plants here just go into hibernation when the sun does not shine for a few weeks and temp is like -40C\nBut as soon as spring hits! They are growing WIIILD",
"Plant hibernation works a lot like animal hibernation. They consume water and oxygen stored in the roots during summer and they try to “turn off” as many functions as possible"
] |
[
"Is there any actual evidence that genetically modified crops are harmful to people or the environment?"
] |
[
false
] |
I occasionally peruse , and the vast majority of people make some pretty serious allegations about the affects of GM crops on human and environmental health. Are there any actual concerns about the current state of affairs or is it another case of the general public fearing something it doesn't understand?
|
[
"GM crops in general are totally and completely harmless. It's pretty much impossible for plant DNA to be harmful to humans in any way - you eat DNA in every single item of food ever made, and it doesn't have any significant effects on you.",
"It is possible to create a GM organism that is harmful. For obvious reasons, inserting the gene for Shiga toxin or something awful into a plant could cause problems. In reality, nobody is spending millions of dollars to make bioweapon food, and the real risks are much less dramatic. The biggest risk is from triggering allergies in unexpected ways. Right now, there are ",
"no products on the market that cause any significant allergic reaction",
". It is possible for something to come up, though, allergies have been seen in ",
"early trials of some products",
", leading to them being discontinued. Still, it's not a huge risk. It's pretty unlikely that scientists will pick the exact antigen that causes severe allergies to insert into their plant.",
"As far as environmental health goes, the risks are pretty light. Most of the criticism focuses on how bad monoculture is. Monoculture is growing huge swaths of identical plants. It's bad because one disease can wipe out your whole field. However, if you've been to any farm in the last hundred years, they're all growing huge number of the same crops. It's just how large-scale farming works. GMOs aren't making the problem any worse than it already was.",
"Lastly, there's the issue of \"superbugs\" - pathogens resistant to pesticides, herbicides, or antimicrobials. For example, since Roundup is used pretty heavily on Roundup-ready crops, it's more likely that Roundup-resistant \"superweeds\" will show up. The key here is that \"superweed\" doesn't mean it can punch through walls or freeze crops with frost breath, it means it's resistant to herbicide. The solution? Switch to a different herbicide. It makes little sense to avoid using a chemical entirely because resistance might develop to it in the future."
] |
[
"That's a consumer rights issue, not a GMO issue, though."
] |
[
"One of my biggest objections to GM monoculture is that some seed companies are using GM to create sterile seedlings so a farmer is not only legally banned but technically banned from saving aside seeds and replanting them the following years. That just seems \"wrong\" to me that we're setting our world's food security upon the continued existence of seed companies and their ability to produce seeds for the farmers to grow food. That coupled with the legal strongarming of farmers to prevent them from doing that very same saving aside of seeds from year to year."
] |
[
"Roughly how long will it be before a manned ship could catch up with, and retrieve, Voyager 1?"
] |
[
false
] |
That little guy is 11 billion miles from Earth at the moment. Astronomers like to think of distances in terms of 'light-years.' Well, we're not anything like a 'light-year,' but we're now a substantial fraction of a 'light-day' from the Earth," says Gurnett. "And I just find that extremely impressive. So, with the current (or predicted) rate of technological advancement, when is it feasible we could catch up with it? I'd like to think that we would so that it could be housed in a museum..but I guess we wouldn't head in that direction unless it were part of a longer trip.
|
[
"Voyager 1's current velocity is only ~3.5AU/yr. The JHUAPL has been working closely with NASA on the ",
"Innovative Interstellar Explorer",
" project, which is a Voyager-style mission with a target velocity of ~13AU/yr. They're looking at several different propulsion schemes, but seem to be focusing on ion propulsion, and don't at all consider their target speed to be out of reach. At one point, they were looking at a launch as early as 2014. Even assuming they don't launch until 2026, the next \"sweet spot\" for a Jupiter assist, it would take just over a decade for the IIE to overtake Voyager, assuming they hit their velocity target.",
"No, any technologies used in this project would likely not translate directly to advances in manned space travel for at least another few decades. On the other hand, the current speed record for a manned spacecraft is 2.33AU/yr, and was set in ",
" by Apollo 10. I wouldn't say we're out of the game just yet.",
"EDIT: Did a bit more poking around, and low estimates for ",
"nuclear pulse propulsion",
" would put workable speeds in the 100AU/yr range, using technologies available in the 50s and 60s. Generous estimates put the max somewhere around 0.1c, or 6,323AU/yr. All of this is of course ignoring the obvious drawbacks of nuclear pulse propulsion, but it's all well within established physical laws. The program was shut down more by the Partial Test Ban Treaty than any concerns about its feasibility."
] |
[
"Show me the blueprints for your designed ship that can carry enough fuel to constantly accelerate at 1 g for 1 year solid. And then explain how you are going to get it into orbit. And then explain how you are going to fuel it up."
] |
[
"Yes, unfortunately.",
"People like to dream of faster than light travel, or even near light travel. but in reality no real physics can even theorize how it could be achieved, at least on the scale of craft that could carry humans and the timescale of a human life.",
"Who knows what we may discover to alter that in 50 years or so from now, that might redefine everything we know. But we don't know it yet. In addition, every passing year makes it more and more unlikely that we could ever catch up to voyager.",
"Sorry to be the bearer of bad news ;)"
] |
[
"Do insects sleep? If so, how?"
] |
[
false
] | null |
[
"The answer first requires that we define \"sleep\".",
"In mammals, we tend to define sleep based on the following criteria:",
"A state of reduced activity and often changed posture",
"A state of reduced responsiveness to environmental stimuli, with the ability to rapidly return to wake if a strong enough stimulus is provided",
"A state that is ",
". That means lost sleep results in increased sleep later and impaired functioning while awake.",
"A state with well-defined changes in physiological signals, including brain activity changes associated with REM and NREM sleep.",
"The last criterion is difficult to broadly apply to other species. For example, monotremes appear to have either a single hybrid REM/NREM stage of sleep, or at least ",
"different physiological correlates for REM and NREM sleep stages",
". Cetaceans are also a bit of a challenge, since they sleep with one half of the brain at a time, meaning that in many ways they are behaviorally awake -- but that is a whole other issue!",
"There is good evidence that ",
"at least some birds have sleep stages like REM and NREM sleep",
". Meanwhile, ostriches seem to have sleep ",
"not unlike monotremes",
". ",
"If we allow some flexibility in the last criterion (i.e., accepting different physiological markers for sleep and wake), then we can very reasonably define sleep in many other organisms, including ",
"zebrafish",
", ",
"C. Elegans",
", and ",
"fruit flies",
".",
"Of the insects, sleep is best studied in drosophila (fruit flies). In drosophila, there are daily cycles of activity and rest. The periods of rest are associated with ",
"reduced movement (often in a preferred location and stereotypical posture) and reduced responsiveness to environmental stimuli",
". The rest state is also ",
"homeostatically preserved, meaning that if you sleep deprive a fly (e.g., by shaking it around when it would normally be sleeping), it will become more sleepy and sleep for longer afterwards",
". ",
"In addition, sleep and wake states in drosophila are associated with ",
"similar patterns of activity of neurotransmitter systems",
" and ",
"similar responses to hypnotic and stimulant drugs",
" as in humans. The ",
"drosophila brain",
" is much simpler than the mammalian brain, but it has similar metabolic and functional demands to the mammalian brain. In mammals, sleep is associated with clearance of certain sleep-regulatory substances (e.g., adenosine), increases in intracellular ATP levels, and pruning of synapses. Similar things seem to be going on in drosophila; for example, see ",
"this",
" and ",
"this",
". In fact, we now think sleep/wake cycles (as we traditionally define them in mammals) may be ",
"something inherent to all neuronal assemblies",
"."
] |
[
"Wow thank you! Very informative!"
] |
[
"Is it possible that sleep/inactivity is the normal state of being and only certain organisms developed/evolved an activity period depending on different stimulus(mostly light) , a period we call being awake ; since what would be called normal was inactivity/rest , the organism must return to that state from time to time for different functions ?",
"It might explain why after millions of years of evolution sleeping hasn't been cut aside."
] |
[
"Is a barrel of compressed air more buoyant on water than a normal barrel of air?"
] |
[
false
] |
[deleted]
|
[
"And thus, the less buoyant."
] |
[
"The amount of air in a contained volume will matter since density is reliant on the mass per volume. The more compressed air is, the more molecular weight it has, the more dense it is in a contained volume. I hope this helped."
] |
[
"No it is less buoyant. Buoyancy is all about difference in density. The less difference the less buoyancy per unit of volume."
] |
[
"What is denser: A black hole or a neutrons star?"
] |
[
false
] |
Thank you.
|
[
" It depends what you mean by the 'density of the black hole.'",
" Neutron stars are generally taken to be the densest form of matter, since black holes are more of a feature of spacetime than a kind of matter with any typical thermodynamic descriptors (pressure, density, etc).",
"The cores of neutron stars reach densities a few times greater than that of atomic nuclei at their cores, maybe reaching around 10",
" grams/cm",
". For comparison, that's like squeezing Mt Everest into a cup of coffee. ",
"Black holes, meanwhile, have reached the point where no interparticle forces can resist further compression, and so all the matter that was used to make them gets scrunched together at a single point called the singularity. Effectively, this acts like it has 'infinite density' since all the mass of the black hole accumulates here and it is pointlike with zero volume. In this sense, black holes are always denser than any matter outside of one.",
"On the other hand, a black hole does have an 'average density' which can be defined from the size of its Schwarzschild radius, which is like the distance from the singularity to the event horizon (the point of no return where the escape velocity is greater than the speed of light). Black holes have this funny property where ",
" black holes have ",
" average densities. This is because the radius grows linearly with the mass while the volume grows like the radius cubed, so the 'average density' decreases like the radius squared - double the mass and radius of a black hole and you've reduced it's average density by a factor of four. In this sense, any black hole more massive than about 3 solar masses is ",
" than any neutron star!"
] |
[
"Quick, concise, and easy to understand. Thank you for your knowledge. :) Opened this thread assuming it was without question a black hole, not realizing there was that much nuance."
] |
[
"Thank you very much for your explanation."
] |
[
"Is the reason you can't see stars in the moon pictures because the sun is shining or the camera quality (or both)?"
] |
[
false
] |
[deleted]
|
[
"Camera quality may be part of it, but the main reason you can't see stars in moon pictures is because the moon pictures were pretty much all taken during daytime on the moon, so the lunar surface (and the astronauts and flags and golf clubs and whatnot) were all extremely brightly illuminated. Think noon at the equator bright, only brighter. Most cameras don't have sufficient dynamic range to be able to show both the extremely bright lunar surface and the faint stars. Think of it like being outside at night under very bright streetlights.",
"So I suppose the secondary question here is: Is the reason we don't see stars during the day due to the brightness of the sun making them hard to see, or because of our atmosphere?",
"The Sun's light gets scattered in the atmosphere, which makes the atmosphere bright. Of course, even without an atmosphere it would still be hard to see stars near the sun in the daytime, but if you stood in the shade you might be able to. The atmosphere, though, prevents us from seeing most other astronomical objects during the day."
] |
[
"When you take a picture on default settings your exposure time is quite small. Exposure time is how long the camera is taking light for. Stars are very faint and need a long exposure time to be taken in a photo. For the moon you do not need a long exposure because it is bright, but to get some features of the moon you will need to zoom in on it. ",
"For the second question it is both. The Sun's light is scattered by the atmosphere lighting up the entire sky and making the whole sky much brighter than any star. "
] |
[
"Ah okay that's what I was wondering :)",
"Had been staring at a framed time magazine on my wall from the moon landings and was thinking about if the atmosphere made that much of a difference in star visibility or if it was simply the sun+reflected light.",
"So I'm guessing the darkside of the moon would have quite an awesome view of space if you can get over freezing to death."
] |
[
"Name of a bird Help"
] |
[
false
] | null |
[
"I think the folks over at ",
"r/ornithology",
" will be able to help a lot more. Thanks for your interest in AskScience!"
] |
[
"Thanks for the help. Sorry for asking in the wrong channel."
] |
[
"no problem whatsoever. Please feel free to ask any other scientific questions you may have in this forum. "
] |
[
"Could enough mosquitos kill you?"
] |
[
false
] | null |
[
"One, could be less than 2 weeks if it was carrying ",
" or yellow fever virus.",
"From the blood loss alone... more difficult. Estimating 3 uL per mosquito and 4.7 L of blood it would take 1.57 million mosquitoes to drain your blood. Average human BSA is 20,000 cm",
" estimating 1 cm",
" per mosquito gives 78.5 feeding sessions, a full blood meal takes 90 seconds so it would take just under 2 hours in total. "
] |
[
"To pick up on a technicality, blood loss can be fatal after losing upwards of 40% of total volume. Using your calculations, this will translate as 1.88 L of blood loss from approximately 627,000 mosquitoes."
] |
[
"Also the time is probably an underestimate as skin perfusion would decline as they went into shock and they would probably be lying down, reducing available surface area. "
] |
[
"How can someone get a new theory evaluated?"
] |
[
false
] | null |
[
"This might be more suited for ",
"/r/academia",
", but anyway:",
"The main thing to do to get a theory out there is to publish a paper in a scientific journal. There's a wide spectrum of journals and especially in broad fields. Journals range from very broad (Science, Nature) to extremely specific to a certain sub-field. Some journals are naturally more influential than others (this is measured with something called the 'impact factor'). Journals with a high impact factor are the best to publish in, but they are more restrictive due to the high number of submissions they receive and the quality requirements they have.",
"After selecting a suitable journal and submitting the paper, the journals editor will briefly evaluate the paper to judge its relevance to the subject of the journal and the basic quality of the paper. The paper is then sent to a small number of reviewers (typically 2-3), who are scientists working in the field covered by the journal. The reviewers read the paper thoroughly and provide feedback. They can recommend the paper be rejected, accepted or anything in between (major revision followed by rereview needed or acceptance after minor revisions with no further review). The editor will decide based on the recommendations of the reviewers and pass the feedback on to the author(s).",
"If the paper has been successfully published the chances of it being read go up considerably. Especially if the paper references related work in the field, the authors of the referred papers will typically take a peek. The peer review process and the screening by the editor are both not perfect, but they do manage to filter out almost all papers that are flat out wrong or offer no value. Which is why most scientists will only read papers in established journals (and drafts only from colleagues that they know).",
"While I can't judge the theory of the electrical engineer you mention, be warned that there are many, many instances of someone claiming to have the solution to a major problem in a field that they're not an expert in. The quantum physics of elementary particles and their interactions is vastly different from the physics you work with as an electrical engineer. The math may have internal consistence, but if some important aspect was overlooked, it may ultimately simply be wrong.",
"Finally, there are people that will claim to have a revolutionary new idea but say they are unable to get the word out because they're being blocked by elitist scientists that don't want their views challenged. And while there certainly is some level of elitism in some fields, most scientists, especially younger ones, love nothing more than to be able to break the existing consensus in their field and work with revolutionary ideas. It's just that true revolutionary ideas come around far less often than some people would like."
] |
[
"Publishing in peer-reviewed physics journals would be a good start."
] |
[
"Others have mentioned publishing the theory in a peer-reviewed journal, but this is basically an insurmountable obstacle for someone outside the field (unless the journal is of particularly poor quality, in which case publishing there won't accomplish anything anyway).",
"I'm going to work under the assumption that this gentleman is not a crackpot, i.e. has a genuine interest in understanding how his ideas do or do not work under the current understanding of physicists. His first obstacle is that any time anyone outside of physics (or even inside physics) says \"I have a theory of everything\" and in particular \"here, I wrote a book about it\" they are automatically labeled as 'crackpot' and ignored. This is because >999 out of 1000 times this is actually the case. I personally get multiple crackpot emails per week and I am not even remotely famous. Physicists just ignore them (or sometimes share the humorous ones with their peers). So he will have to work very hard to get inside 'the establishment.' On the other hand, I've happily worked with non-physicists (mainly semi-retired folks with an interest in physics) who genuinely want to understand the current state-of-the-art.",
"There are a few things that are required for a non-physicist to actually start doing physics, and they are essentially equivalent to actually becoming a physicist:",
"And always remember that a new 'theory of everything' must explain ",
", in addition to explaining something new about reality ",
" making predictions that aren't made by existing theories. There's simply no way to know that your theory will work unless you're already an expert, so you have to become an expert."
] |
[
"How can vegetables be grown at accelerated rates in indoor farms?"
] |
[
false
] |
How can they make it grown two times faster, and why are this farms not widely used? I know the precise wavelength of light is involved, but do nutrients and light schedules are taken into consideration or is it something special behind this accelerated growth.
|
[
"Basically you can 'optimize' conditions for plant growth i.e. provide the exact amount of water, the correct balance of nutrients, soil or hydroponic conditions and length/ intensity of (sun)light. ",
"Under natural conditions these are going to be over or under provided thus reducing plant growth efficiency. If you want more details, feel free to ask.",
"Source: Ecologist studying the effects of drought on plant traits. I regularly use greenhouses to control all the above conditions."
] |
[
"Is there a table where I can check all of this for different vegetables? ",
"I can dig around in some journals and let you know. Off the top of my head no. There are loads of books out there that give great advice. You can pick them up for about £20/22-24$. I will PM you some names.",
"When it comes to temperature is it more important the soil temperature or the air temperature?",
"Generally air temperature is used. Normally as long as a frost is kept from the plant, they will be happy down to a low temperature."
] |
[
"Thank you! is there a table where I can check all of this for different vegetables? when it comes to temperature is it more important the soil temperature or the air temperature?"
] |
[
"What happened to the Global Cooling scare of the 1980's?"
] |
[
false
] |
Not that I don't believe in global warming or anything, but im just generally curious
|
[
"There wasn't a Global Cooling scare in the 1980s. The people who claim there was are lying in order to sell their bigger lie that there's doubt about global warming.",
"Where does the myth come from? Naturally enough, there is a kernel of truth behind it all. Firstly, there was a trend of cooling from the 40’s to the 70’s (although that needs to be qualified, as hemispheric or global temperature datasets were only just beginning to be assembled then). But people were well aware that extrapolating such a short trend was a mistake (Mason, 1976) . ... Probably the best summary of the time was the 1975 NAS/NRC report. This is a serious sober assessment of what was known at the time, and their conclusion was that they didn’t know enough to make predictions.",
"--",
"The global cooling myth"
] |
[
"Here is ",
"a graph showing the frequency of \"global warming\" and \"global cooling\"",
" in books from 1970 to 2008, based on data from the ",
"Google Ngram service",
". It shows that \"global warming\" was mentioned 3 to 50 times more often than \"global cooling\" in the 1980s. In the 70s they were pretty much tied, but both occured at 1000 times lower levels than global warming had in 2008. This backs up the claim that there was no global cooling scare in the 80s, and that global cooling has never had the amount of attention that global warming has now."
] |
[
"I distinctly recall hearing about a possible coming ice age when I was in elementary school in the mid 70's. Could have been on \"In Search of...\" I grew up going to the La Brea Tar Pits and was fascinated by the remains of pleistocene animals, so talk of another ice age stood out."
] |
[
"How small can a star be?"
] |
[
false
] |
Eventually: how small is the smallest known star?
|
[
"Stars start to fuse hydrogen at about 80 times the mass of Jupiter. Below this, they are brown dwarves. Above about 12 times the mass of Jupiter they also fuse deuterium, and this is a grey area as to whether you want to call these stars or not."
] |
[
"If by \"small\" you mean radius, neutron stars can be as small as 12km in radius, approximately the size of a large city. However, these stars are still very massive and therefore incredibly dense. A common way of expressing this is that one teaspoon of a neutron star would weigh a few billion tons."
] |
[
"The smallest hydrogen burning stars are red dwarfs with about 80 Jupiter masses, with a diameter only slightly larger than Jupiter (they are much more dense). Dead stars, like white dwarfs and neutron stars, are much smaller, but much more massive than a red dwarf."
] |
[
"Why is it that sometimes if you get a cut it won't hurt until you notice the wound?"
] |
[
false
] |
Example: today I was spraying something with a hose and I guess the metal cut my hand. I didn't feel it at all until I noticed the blood trickle onto the hose and my hand was covered in blood. It was a pretty decent sized cut too. Only when I looked at it is when it started to sting. Isn't pain supposed to let you know when you've hurt yourself? Why didn't it hurt when it happened and only after I looked at it? Edit: , neuroscience, . Edit 3: Thank you all for answering my question! To those who were wondering, no the wound wasn't that deep and it's healing fine. Also, I was not asking for medical advice, just wondering about the experience of delayed pain.
|
[
"If you were applying pressure to the area of the wound (holding the hose?) then ",
"lateral inhibition",
" is likely your culprit here. Your nerves were detecting pressure to the wound and that was minimizing the pain feeling."
] |
[
"I would say from a psychology standpoint, you were probably putting a lot of your attention into whatever you were doing and your brain decided it really wasn't that important to be brought to your conscious attention so you were unconsciously dealing with it. Then as you became consciously aware of it by seeing it, your brain was like \"ah fuck, might as well let them in on our little secret.\"",
"Edit: After doing a little more research (still from a psych standpoint so I won't get into pain or anything like that), I found that inattentional blindness may be at fault. That is, you only remember and perceive events or details unless you're giving them a fair amount of focus. So you're taking in all of this stimuli, visual, auditory, olfactory, and touch, so it's easy for your brain to just put some things on the back burner and not bring your attention to it because it's not the hugest deal in the world at the time. \nAlso, the pain you were experiencing unconsciously may have been what brought your attention to it in the first place. Like, your nerves are firing telling your brain that something's gone wrong at your hand but not enough neural impulses have been received to make it important, but eventually you reach the threshold where it does seem like you should be focusing on it so your unconscious self tells your conscious self, \"Hey, look at your hand, it might interest you\" and then you realize it's cut. So yeah, there's that."
] |
[
"I can't speak to tactile sensation, but attentional effects would explain this type of effect for other sensory modalities. It's a phenomenon known as ",
"selective attention",
" and it can cause you not to notice a lot of different things. "
] |
[
"Is there any evidence of two seperate planets orbiting an object in the same path but not colliding?"
] |
[
false
] | null |
[
"The simplest way for this to happen is for a smaller object to be a Trojan at a Lagrange point of a larger object. ",
"The Trojan asteroids around Jupiter",
" are an example. Saturn also has Trojan moons: Callysto and Telesto are co-orbital with the larger moon Tethys."
] |
[
"Epimetheus & Janus - moons of Saturn",
"https://en.wikipedia.org/wiki/Epimetheus_(moon)",
"https://en.wikipedia.org/wiki/Janus_(moon)",
"Explanation with animation - ",
"http://www.ac-ilsestante.it/en/ASTRONOMIA/i_grandi_astronomi/Newton/animazioni_newton/janusepime/janusepime_newton/janusepime_newton_01_blocco_popup.html"
] |
[
"Although strictly speaking the smaller one would be a moon. And it does have to be significantly smaller. If you tried it with a double planet, it would be unstable. Like when ",
"Theia",
" got too big and collided with Earth. Or the rest of Earth, given that Theia makes up a significant portion of what we now call Earth."
] |
[
"Why is the speed of light the universal speed limit?"
] |
[
false
] |
Title says it all
|
[
"A postulate is something that you just start off with. You say \"Let's suppose that ",
" is true. Then what?\" And it turned out that supposing light travels at the speed of light (relative to ",
" observer), meant that everything just ",
", and he managed to develop a testable theory (that of Special Relativity, and later, General Relativity) that has stood up to every verification. ",
"The reason the postulate was made was because in the late 19th century, it became clear that light was an electromagnetic wave and the equations that governed the propagation of EM waves predicted that light traveled at a constant speed. People then started asking ",
" and no one could quite find an answer, until Einstein said ",
"Edit: Wow thanks for the gold!"
] |
[
"I could give you a lot of different answers or explanations, but it would all be circular. The reason is this- it's taken as a postulate, or assumption, in the theory of relativity. It's a very good assumption that agrees with every measurement ever made, but it's an axiom of the theory, which we take to be true from the beginning. "
] |
[
"This question really cannot be answered with anything but \"because that''s the way the universe seems to work.\" ",
"I know this seems unsatisfying, but at some point, we have to accept that this is just a fact we experimentally discovered and built a theory on. ",
"If you are interested in the math, check out a derivation of the Lorentz transformations (",
"like this",
"). This will most likely be the closest thing you will find to an explanation. "
] |
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