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In basaltic magma, how much is recycled crustal material and how much is mantle material? I'm curious about both mid-ocean ridge and mantle plume/hot spot magmas, and potential differences between the two. From what I can gather, granitic magmas usually result from recycling of crustal material at subduction zones; but I'm not so clear on the composition of basaltic magmas. How much of the material at mid-ocean ridges/hot spots originates deeper in the mantle and is brought up by convection, and how does this interact with the astenosphere and moho? Thanks! I believe that the magma that has the greatest amount of crust recycling is in a subduction zone such as the one around Oregon and Washington states. The oceanic crust slips underneath the continental plate, melts in the mantle, and then feeds into the volcanoes in the area.
What is it called when the products of a chemical reaction inhibit further production of the same chemical? Same with when the products of a chemical reaction facilitate more production of the same chemical? The phrase sympathetic and parasympathetic keep coming up, but I an't find them in the right context. In biology and especially when talking about metabolic pathways, you would use the terms negative feedback and positive feedback, where a metabolite allosterically regulates the activity (positively or negatively) of an enzyme earlier in the pathway. For example, the first step of glycolysis is the conversion of glucose to glucose 6-phosphate by hexokinase (in muscle). Hexokinase is inhibited by a G6P, an example of negative feedback. When metabolites impact the activity of enzymes 'downstream' on the pathway, we call that feedforward activation or inhibition.
Why does Venus rotate in the opposite direction to the other planets in our solar system? This is due to the impacts by asteroids in the early years of their formation. No, this is generally the consensus answer any longer in planetary science. Some 30 years ago, this was the standard explanation why Uranus' and Venus' odd axial tilts were the result of giant impacts. Bear in mind, though, that this was relatively soon after the Apollo missions had confirmed that our Moon had formed via giant impact (although there's evidence now that even this may not be so straightforward). So, this may have been a case of "when you have a hammer, everything looks like a nail." Giant impacts started being used to explain everything a bit odd in the solar system. Uranus is weirdly tilted? Must've been hit by something! Huge cliffs on Miranda? Must've been hit by something! Weird two-tone coloration on Iapetus? Must've been hit by something! Neptune has a mysterious source of internal heat? Must've been hit by something! This hypothesis started waning about 15 years ago when impact simulations were getting good enough to show that it's exceptionally difficult to produce an impact that's large enough to tilt Uranus but not completely obliterate the planet. It's a little more likely to do this with multiple impacts, but still not exactly easy. The most likely scenario at this point is that Uranus had some kind of gravitational near-miss, enough to induce a tidal torque that could turn its axial tilt. There's also some evidence that this scenario would require ejecting some mass in the process, possibly a big moon. The remaining moons would eventually fall in line with the new inclination angle of Uranus' equator due to tidal forces acting over billions of years. This explanation also has the neatness that it may explain why Uranus doesn't have a big moon, which we'd expect from most formation scenarios; moreover, there are at least some formation scenarios that suggest Uranus and Neptune swapped orbits early on, providing ample opportunity for this gravitational near-miss to occur. For Venus, meanwhile, it turns out you can get the planet to slow down to almost a standstill with just solar tides acting on the thick atmosphere when applied over the age of the Solar System. (Not only does Venus rotate backwards, but it also does so exceptionally slowly, with one rotation every 243 days.) Explaining the slight backwards motion imposed on top of this virtual standstill is still a little tough, though there's some hand-wavy explanations that additional tidal torque induced by Earth might do just that.
Does exercising in the morning really increase your metabolism all day vs exercising any other time? I've asked this question before and got no responses (~1 month ago), so I figured I'd try again. I hear this claim often spouted here on reddit and is "common" knowledge among gym goer's, but it never made sense to me. I don't see how the metabolic response induced by exercising would be any different depending on the time of day. Nope. It's a myth, like locational fat burning (eg. doing crunches to burn tummy fat) or burning more calories at a lower heart rate. Metabolic rate spikes after exercise but then tails off after a few hours back down to slightly above the BMR for up to a couple of days regardless of time of day you start the exercise. The amount it spikes by is pretty closely related to how hard you exercise. You perform better later in the day (optimally around 6pm), and you have the best mix of temperature and hormones at that time to avoid injury in comparison to training with cold muscles first thing in the morning too. HOWEVER There are a bunch of studies that show that exercise first thing in the morning is more habit forming than exercise later in the day. Personally I don't believe in relying on some motivation or inspiration to achieve an ends. I think you have goals and you train yourself to have habits that satisfy those goals. You don't need to motivate yourself to get out of bed and hit the gym, it's just what you always do. Which is why I tend to train first thing, despite the slightly elevated risks.
How are temperatures as high as 4 trillion Celsius contained? Doesn't a temperature that hot melt everything around it? Searched Relevant discussion Original question by speed_is_all_I_need Take the Z-Machine for example. How do you contain 6.6 billion degree temperatures? I feel like it would melt nearly anything in an instant. What materials would be needed to create a heatsink that could deal with those incredible temperatures? Top comment courtesy iorgfeflkd These things are generally confined by magnetic fields in vacuum. Heat doesn't transfer through a vacuum, so the interior of the chamber doesn't get melted by the heat of the plasma. In collisions at CERN and Brookhaven National Lab, temperatures have reached the trillions of degrees, but it's only in the volume of an atom that things get that hot.
Is it possible to know things in your dreams that you don't know in real life? The second one. It's possible to access memories/knowledge that you might not be able to access (or at least not find yourself in the correct context to access) while awake.
The Mormon Church Released pictures of the "Seer Stone" reportedly used by Joseph Smith. Can you make a geological analysis of it? I'll give this a whirl, it's not everyday that one gets first pick at looking at a sacred relic. First, the shape. That is a prolate ellipsoïd with very well devellopped rounding. There is definitely no faceting such as you'd find on a glacially derived cobble. The shape, roundness and exteranal smooth texture are consistent with transport in a fluviatile system (in other words, that pebble was picked out of a stream or from fluviatile deposits). Also a word about the polishing and patina. Either that rock was waxed, laquered or varnished in some way, or else it was handled , enough to acquire that shiny yellowish patina. Now, the material. The quality of the picture is so-so. I'd be all over that pebble with a handlens before I said anything with confidence. From what I see in the pix, I'm thinking more along the lines of metamorphic than straightforward sedimentary (although I'm leaning towards meta-seds). That comes mostly from the wispyness of the lamination, the sharpness of the contacts on both sides of those quarto-feldspathic laminations (no grading). But I'm not setting this down as a definitive ID. So: metasedimentary (Say, a metawacke or somesuch), conditional to a examination with a handlens. What I'd be looking for with the handlens is whether it is made of rounded grains (And thus a Sandstone) or whether it was made of interlocking crystals (which would make it metamorphic in this case). I'd also look for evidence of deformation and a comple of other processes (is that sedimentary lamination? could it be metamorphic ribboning or even migmatisation?) You may also want to give the rock a whirl on /r/geology and see what we might have to say about it there. Perhaps some of my colleagues which are more familiar with the geologic particulars of the american mid-west will feel some familiarity with that specific lithology and have an Eureka moment. I'm pretty sure /r/askhistorians might have a ball commenting on this as well. Finally, I'm by no means well informed on Mormonism, but you metionned this is called a "Seer Stone"? Any chance that might be in relation with the fact that when looked at perpendicular to the laminations, the intersection of these laminations with the surface of the pebble generates a concentric pattern of ellipses, somewhat like an eye? Would you perchance happen to know if early Mormons had any cultural dealings with the "Doctrine of signatures" (the belief that the properties of things were influenced by their appearance)? EDIT/UPDATE: To all users mentionning the stone is supposed to have been picked up in NY state and not the american midwest; thanks for bringing that to my attention. As previously stated, I claim no familiarity with the history of Mormonism, just geology. From what I've been made to understand, the provenance of the stone is a matter of historical interest as it is referred to in Smiths texts. What I make of that is that it's sourcing in a well upstate NY is a hypothesis to be tested. But there is only so much one can say without direct access to the specimen. Let it just stand that while there is nothing I can see from OPs pix which is inconsistent with a sourcing of that pebble in upstate NY (or a well for that matter), there is nothing either to exclude other origins. Some users have suggested other origins which might perhaps be testable. One of the most intriguing was set forth by /u/WRCousCous , who suggests based on his experience with amerindian artifacts that the patina and general aspect of the pebble might be consistent with a type of artifact known as a "thunder egg". Apparently this would fit in with a documented fascination by Smith with native artifacts and culture. Anyways, this is a quite enjoyable discusssion for I which I thank contributing users, and an excellent exemple of something I have always deeply believed: even the smallest stone can be an object of intense interest and fascination.
What stops an electron from falling into the protons within an atom? what stops the negatively charged atom from being attracted and falling towards the positively charged protons? Because of quantum uncertainty, the electrons are already as close as possible to the nucleus. People sometimes explain this as an consequence of quantum mechanics. This is far from obvious; for example it would be false if our Universe had 4 spatial dimensions, and electrons fall into nuclei even with quantum mechanics. For simplicity, let's consider the hydrogen atom. I'm gonna work with orders of magnitude here, so I'll leave out some numerical constants. So, the hydrogen atom essentially wants to lose energy. It will lose energy by emitting radiation until it has reached its lowest possible energy state, if such a state exists. In classical electrodynamics, such a state doesn't exist: the electron and proton continue spiraling in emitting greater and greater amount of energy. In a finite time p and e join having emitted an infinite burst of energy. This clearly does not happen IRL and is quantum mechanics that comes to the rescue. But before we deal with it it's important to understand that e does not necessarily move towards p because there is an attractive force. e just wants to lose energy, that's all, and it will do so until it has energy left. Energy is potential + kinetic. Potential energy is what yields the attraction; between electron and proton at a distance Δx this energy is E_p = - e /Δx Note this energy is and decreases as the electron is brought closer to the proton. So if we were to just make this as small as possible we would obtain that the e wants to get near the p, which makes sense. But there's also kinetic energy. This is E_k = p /2m Where p is the linear momentum of the electron and m is essentially the mass of the electron (you can derive this from E_k = 1/2 mv and p=mv). Now, since classically we can change Δx and p to pleasure it looks like we can make E_k zero by sending p to 0 and E_p arbitrarily negative large by shrinking Δx. So the atom should be able to lose infinite energy and e and p join, just like I said above. In quantum mechanics, however, we will reach a limit in the form of uncertainty. Heisenberg's uncertainty principle is something like Δx Δp > hbar. So trying to confine the electron in a small space is gonna bound p to have a typical value not smaller than p ~ hbar / Δx. This changes things. Rewriting the total energy using the HUP: E = E_p + E_k = - e /Δx + hbar /(2m (Δx) ) = - A (Δx) + B (Δx) I've defined the positive constants A and B; their value is not important. You can see that this function attains its minimum at a distance Δx different than zero. You can just plot it in Wolframalpha, choose any random (positive) values for A and B and you'll see what I mean. So the electron will not join the proton; it will lose energy through emission of radiation until it is in the lowest energy state which has it at a nonzero distance from the proton. If you did all the calculations, this nonzero distance would be on the order of the Bohr radius. Intuitively, to recap, the electron will get closer to the proton until it's localized in a region so small the uncertainty in momentum grows, and this makes the kinetic energy higher much faster than the potential energy gets lower. So this "uncertainty force" pushes back against the Coulomb attraction. Equilibrium is found at around the Bohr distance. That's of course a very heuristic argument. You redo the calculation in actual QM (instead of what we did here, which is a semiclassical/orders of magnitude analysis) and more or less the same comes out, but you also know the exact values. But all the essential reasons for the electron not to fall in the proton are above. (Bonus round: why doesn't uncertainty prevent collapse if there are 4 or more spatial dimensions? Well, because the Coulomb potential has a different form. It has behaviour (Δx) where D are the spacetime dimensions. The "uncertainty energy" always goes as (Δx) . So the thing above does not work. In general one should be wary of handwaving the "uncertainty fixes all divergences" argument because in many physical systems it can be completely wrong.)
Why can I tell when a tv has been turned on from really far away, even when nothing is playing on it? In sixth grade we would often watch a short educational film after returning from "specials" (gym and the like) and the tv would alread by setup when we got back. I began to notice that I could sort of 'hear' that the tv was on in the classroom, long before we got there. The best way I can describe it is that there's just sort of a buzz that I'm aware of, and that means a tv is on somewhere. remember nothing is playing on the tv. This happens even if the tv is just on a black input/line/tv-video screen. Anyone know what's going on here? Can everyone do this? A TV's electronics generate around 500 lines at 30 frames per second, or ~15000 Hz, which is at the upper threshold of human hearing. Lots of adults can't hear the noise due to high frequency hearing loss. Edit: I'll add that this is similar to the noise of power transformers - i.e. the so-called "60 Hertz Hum"
Do LCD monitors emit outside the visible spectrum? Chemist here, had someone ask me to tell them what wavelengths are emitted by a computer monitor. (They are doing research on eye disease) I don't have a set-up that will allow me to do emission spectroscopy on anything as bright as a computer monitor, or even an iPhone. LCD spectra would be limited to the type of backlight used. CCFLs are the most common, so you can look up the spectra for those. LEDs should generate even less non-visible light due to their higher efficiency.
Physics and Psychology of Music Question: Why do the lengths between the frets on a guitar get smaller and smaller? So, I know that the sensation that humans hear as pitch corresponds to the frequency of the sound wave - a note that may considered to be high/low has a sound wave with a higher/lower frequency than the sound wave of the origin note. In western music theory the difference between pitches (or the interval between pitches) is quantized in units of whole steps and half steps (with two half steps making a whole step). To my ear, the half step (or semitone) between both A4 (440 Hz) and A4 (466.16 Hz) and, say, D5 (587.33) to D5 (622.25) is the same "distance," musically. But obviously, by either doing the math or looking at one's guitar fretboard* (example ), the actual frequency difference between those sets of notes are not equal. Why? What is the difference between musical pitch and physical frequency? Has spending my entire life listening to only music built on western music theory conditioned my brain to recognize those frequency differences as "half notes?" General comments on the connection between the physical phenomena of music, its theories thereof, and its perception by humans are also appreciated. *The frets on a guitar are equivalent to the keys on a piano. A specific fret or key corresponds to a specific note (frequency). Frequency is related to pitch on a logarithmic scale...each time you raise a pitch an octave, the frequency is doubled. That is why the difference between your A and A# is different than that of the D and D#. To compensate on a guitar, the fretboard must also be built "logarithmically". Guitar#frets
How do we know that the universe is expanding everywhere, as opposed to just around us? One of the ways that inflation is traditionally taught in schools is to half-inflate a balloon, draw "galaxies" on it, and then further inflate it. I realized suddenly recently that this "view" of the universe assumes that we, the observers, are at the center of the balloon. I mean this in the sense that all of our instruments with which we've gathered our entire understanding have only existed (roughly) within the confines of our solar system, and so instrumentally we've only established that the universe around us is expanding. I'm curious to know on what grounds we reason that the universe everywhere is expanding. It seems like a reasonable assumption to make, and presumably it matches with our observations and models. I guess I'm wondering whether the hypothesis of local inflation (or inflation only around large masses) is something that's been specifically tested/reasoned about. I.e. is inflation uniform at cosmic scales, or "spotty" (up to the extreme hypothetical limit of "only one spot, and you're in it"). You've missed the point of the balloon analogy. In that example, we aren't at the center of the balloon, we're on the surface as well, in a curved 2D universe. Ignore the volume of the balloon. If you pay attention to the surface, you'll notice that every point on the surface is moving away from every other point, so regardless of where you pick the observation point, you will see all the surrounding points moving away from you.
At what scale would the "hold my finger over the tip of a straw and pick up water" effect no longer work? All kids play around with the straw in their drink and hold their finger over the tip of it and pick up some of the fluid in the straw and then release their finger dropping it back into the cup. This is due to a combination of the vacuum created in the straw and the surface tension of the liquid at the end of the straw I presume. At what scale would this no longer work? Could a giant space alien with a giant straw dip into the pacific ocean and grab a bunch of water with its finger over the tip of the straw? For the liquid in question lets try using fresh water to keep it simple. Im not sure how much difference salt water makes in the question. At about thirty-four feet, which would correspond to about fifteen pounds per square inch of pressure at the bottom of the straw. Atmospheric pressure at sea level is about 15psi, and that is what is keeping the water up the straw; pull the straw higher than 34', and an empty space will begin to form above the water at the top of the straw. EDIT: I answered the wrong question!
Biological question concerning the relationship between mitochondria and it's prokaryotic homologies. If a prokaryote, let's say a bacteria, truly is closely related to the mitochondria, then would that mean antibiotics targeting the ribosomes of bacteria would also target mitochondria? Or is the genetic differences too great? Yes! See Zyvox for one example. Mitochondrial ribosomes are actually quite similar to their prokaryotic brethren. It's true that there are some exceptions to the universal genetic code that we've only found in mitochondria, but this has nothing to do with the ribosome; rather, these differences are due to mutations in the tRNA and amino-acyl-synthetase genes, which actually do the work of interpreting codons and assigning amino acids. The ribosome itself doesn't have any defense against a mischarged tRNA.
How do we determine and measure the average temperature of Earth? I assume that the average temperature of Earth changes based on multiple variables: Distance from the sea/ocean, altitude, hours of daylight, time of day etc. What are the criteria for measuring the average temperature of Earth? I also assume that each nation gives their own averages, but how do we determine the weights for each country? For example Russia is a lot bigger than Luxembourg, so Russia should have more variation in temperatures and their landmass should represent a larger proportion of the average temperatures. I would bet each principal investigator of global temperature changes would calculate that in a unique well-reasoned way. Your question may be best revised to be "What well-regarded agencies and scientists are there that measure global temperature?" And then looking into/asking them their methods. Here's a good video on satellite measurements https://www.sciencelearn.org.nz/videos/118-satellites-for-atmospheric-measurements
What would the day/night cycle be like living on the moon? There is no "dark side" of the Moon. There are permanently shadowed craters near the south pole (maybe the north as well, I'm not sure), but that doesn't really constitute a side. What's often called the "dark side" of the Moon is better called the far side of the Moon - the side not visible from Earth (it's actually less than half of the surface of the Moon that we can't see, but that's not important right now). This side has the same sort of day-night cycle as the near side: about four weeks. No. That would be a lunar eclipse. A new Moon is when the Moon is located roughly between the Earth and the sun. The sun is shining on the far side of the Moon, and not on the near side. We can only see the near side, and that side is in the shadow of the Moon during the new Moon, making it dark and therefore difficult to see from Earth. Yes. It's an even better source of light on the Moon because of its greater size and higher albedo (a measure of how much light is reflected by the object in question). About four weeks long. The Moon is tidally locked with the Earth, which means that the same side always faces the Earth (with some very small variation that we'll ignore right now). The Moon therefore takes as long to rotate once around its axis as it takes to revolve once around the Earth - about four weeks. This makes days and nights two weeks long apiece. So the city in question would have two weeks of day and two weeks of night.
Why do banana peels turn brown so much faster once it has been peeled? So I looked it up and apparently the contact with oxygen causes an enzyme called polyphenol oxidase (there are other enzymes too) to increase/start chemical reactions that produce melanin. Melanin is a strong pigment. Interestingly melanin is the same molecule that give people skin pigment, which protects us from UV rays. http://www.ncbi.nlm.nih.gov/pubmed/6794984 http://en.wikipedia.org/wiki/Polyphenol_oxidase https://suite.io/helga-george/3mq829r Side note: I guess this means pigment was evolved and highly conserved a very long time ago, when animals and plants had a common ancestor. Also, Im wondering if this rapid increase in melanin is a response by plants to produce melanin which can protect them from the harmful effects of UV rays (the oxygen being a signal that sensitive parts of the plants ar ein open air)
Can you create a machine learning algorithm to create a computer virus? So I have seen a lot of machine learning videos, including , , , . Then, I also saw . It made me think about since there are so many ways to produce machine learning algorithms in so many disparate fields and to do so many things, could you have an xkcd style virus-farm and try to use machine learning to look for security holes? The MarI/O simulator found a glitch in Mario, on so it might not be too far a jump to consider that a really advanced neural network might be able to evolve a way to hack computer systems? If so how would it work? Note: . I just thought it would be an interesting idea. Sure. Check out the DARPA cyber grand challenge for an example of fully automated exploit creation. They didn't use ml but in principle it would work. But remember that ml isn't magic. It is sophisticated curve fitting. So I wouldn't worry about this having any worrisome implications about dystopias or whatever.
What would the W and Z mass be without Higgs ? Just like technicolor, already in QCD the exchange of gluons in the spin zero, isospin zero channel is attractive, causing the formation of a quark condensate, which dynamically breaks chiral symmetry : SU(2)_L x SU(2)_R -> SU(2)_V The corresponding would-be Goldstone bosons contribute to the longitudinal components of the W and Z. In my understanding, the reason for introducing the Higgs is that the QCD condensate contribution is much too small for the W,Z phenomenological mass. Would anyone know of a reference were the QCD condensate contribution is evaluated ? My searches failed and I would be very grateful. Take a look at the following: http://arxiv.org/pdf/hep-ph/0203079.pdf (see p.14) and this comment from Matt Strassler: http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-apparently-elementary-particles/the-known-particles-if-the-higgs-field-were-zero/#comment-133
If teleportation will be available for human transportation, will the individual that "arrives" at a certain location be the same but not the original that "departed" from another location? That's one way to do it. Probably the only theoretically possible way we have right now. But I'm hoping for another way that actually transports your matter intact.
Microbiologists and biologists of Askscience: Is it true that not washing hands will "train" one's immune system? I regularly get mocked for refusing to eat without hand washing. My friends assert that touching food with dirty hands is healthy because it will keep their immune systems in shape. I guess they mean that inoculating a fairly small amount of bacteria or viruses isn't harmful for the body because this will help it to recognize the pathogens. My idea is that they are incorrectly applying the idea behind a vaccine to live microbes; it is also proved that spending some time regularly in a wood or forest is a huge immune booster. Just not washing hands is plain stupid and dangerous. Am I wrong? Just to clarify, I am not a paranoid about hygiene. I just have the habit of washing hands before eating, because my parents told me so when I was young and I picked the habit up. again: thanks for all the responses! You're not wrong. Bacteria is good, but that's the non-pathogenic form. Most pathogens that cause disease in us have mechanisms that can specifically override our immune system. Just because you expose yourself to that bacteria doesn't mean you won't get infected. That's why they at least kill the pathogen before vaccinating you with it. What immunologists mean when they say germs are good is that you should get exposed to germs from a natural environment, where almost all of them will be non-pathogenic to us (like in the woods as you point out). One arm of our immune system gets activated by ANY microbe, pathogenic or not. And that arm apparently expects some amount of activation at all times, without which it kinda gets screwed up. But in an urban jungle, almost everything you find around yourself (especially your kitchen) is probably some kind of organism that can do something wrong to you, so the benefits of giving some stimulation to your innate immune system is outweighed by the risk of contracting some serious problem. So the end-message is, go out and play in the ground, venture through woods. But WASH your hands before you eat while you're in any major human establishment!
Can an average consumer find/afford solar panels that easily "plug in" to regular appliances (i.e. window air conditioner) AND provide adequate power? Is this possible? Its hotter than Satan's va-jayjay here but I feel so wasteful having the AC on 24/7. What equipment (size of solar panel, converter, etc.) would be needed to power the unit, which plugs into a standard U.S. three-prong outlet, for even just a couple hours per day? Along with environmentally friendly, I'd prefer to be wallet friendly too, if you know what I mean. Usually you'd hook your solar panel into your home energy grid - that way, if you make more energy than you burn on just an AC, you can use it for everything else in your house (things like the fridge and washing machine are big ones, for example, but even lightbulbs add up). It doesn't matter that a solar panel is attached to a specific appliance, just that it covers as much energy as possible/practical including, hopefully, an AC or more. I understand the associated guilty feeling of what seems like a willful burn of energy from the AC, but it all adds up to the same thing in the end, so don't worry about one specific appliance or the other. Another advantage is that depending on where you live and how your power company operates, you can get paid to pump energy into the grid. I'm not too sure on the details of this but I know that it occurs on some level. If you live in a sunny area (and it sounds like it), a solar panel can definitely help contribute to your electric bills and increase the value of your home. I think it's not too hard to get 150W per square meter (how much space do you have?), I don't know what your situation is but you could probably do better given climate conditions. You'd have to double-check that efficiency for whether its current, and both it and pricing are going to vary per model (the business has become much more competitive lately now that it's becoming mainstream). You can calculate if it's going to be worth it or not, which if I know a few more things about your house/region/utility rates I could give you a (very) rough estimate on, since I've done it a few times. If it's the AC you're worried about, I don't know what model, setting, or time schedule you run it on, but if it's an old junker running frequently it can bang up to 1000W! This can vary a lot, so it's hard to say, but they're definitely extremely power-intensive. It's always good to reduce your power usage in the first place, which is always superior to covering that with renewables - it's generally much cheaper and less of a hassle. Ceiling fans are much more energy efficient, but of course they also don't work as well - still, it means you could run your AC on a lower setting, or for less hours in the day. There's other various retrofits that you can do to your home in this vein that can be extremely cheap and easy (something like painting your roof white). If you bring up the region you live in and your power usage profile/monthly power bill, I can go further on this tangent, but ultimately, yes you can certainly get a solar panel that could very possibly pay for itself and more, though it wouldn't function as a standalone unit and would instead help supply the entire energy needs of your house (which is easily the best way to do it, since if - say - it's early morning and you get sun but don't need the AC yet, you can use that to run your coffee machine).
Relativity says that there is no "right" perspective. That seems to imply that the universe isn't in one particular state at a given point in time. What does that mean and how is this possible? incorrect to say that the baseball exists at a finite location at a specific point in time? No it's perfectly correct, the problem is that the numbers you get are unique to your reference frame and not values you should expect others to share. it's actual location in the universe There is no such thing. Relativity bans the notion of absolute space, the idea that the whole universe sits on some absolute immutable and ultimate stage that cannot change and retains primacy to all other viewpoints. Also wouldn't this have to mean the baseball doesn't exist in one state at a time but rather infinite states and what would that even mean? Take this idea. There is a baseball at rest (with respect to you) 5 feet from your left. Now I'm heading towards you and the baseball at 0.9c (with respect to you). You will say, the baseball is 5 feet to your left and I'm 1,000 feet away approaching the baseball at 0.9c. Conversely I will say, the baseball is ~435 feet away and heading towards me at 0.9c. You are still 5 feet to the left. Isn't this a weird disagreement we have? And it's how the world works. Now, we obviously can't have the baseball in two spatial coordinates at the same time, but then the phrase "same time" loses meaning--we disagree on each other's clocks too! What a mess! Luckily, because of how Lorentz geometry works, when I slow down and come to rest with respect to you, we will now agree completely on spatial distances and the baseball will be in the same spatial distances we both measure. We will find ourselves in the same frame of reference, but disagreeing on whether or not the baseball is 5 feet to your left or not. Once I leave our shared reference frame however, I cannot make this statement anymore in general.
What's actually happening to your rods and cones when your eyes are adjusting to the light/dark? I understand that when your eyes adjust to the light or dark that it takes time for your rods and cones to adapt to the change in condition, but what's actually going on with the cells for this to happen? When your rods and cones adapt to bright light, what is happening is they are "photobleaching". When rods & cones are bleached, they cannot process incoming light. Here's a short mechanistic description of photobleaching from this paper : As a result of the work of G. Wald and his group [ 1 ] it is known that 11-cis-retinal, the prosthetic group of rhodopsin, undergoes stereochemical changes as a response to light absorption, leading eventually to all-trans-retinal. It is generally believed that retinal is then removed from its apoprotein opsin; the original light-sensitivity of rhodopsin is restored when, through a cycle of reactions, 11-cis-retinal is again linked to the protein. So essentially, light starts a process where 11-cis-retinal becomes detached from the rod or cone cell, and it eventually becomes attached again. However, since you're constantly being exposed to light many of your rods & cones are bleached since they can't be restored instantaneously. So since many of your rods & cones are bleached, the light doesn't overwhelm your retinas. In the dark, since there isn't much light to stimulate your rods & cones, more of them remain unbleached and you can more effectively pick up on the little bit of light that is there. Fun facts: This is why when you open your eyes to bright light after having them closed for a while everything appears to have a blue tint! Rods respond to slightly blue light, but normally when you are in the light many of your rods are photobleached, and they "unbleach" much more slowly than cones. When you've just had your eyes closed for a very long time, all of your rods become unbleached.
How did the Big Bang not form a super massive black hole? So, when a star's mass exceeds a certain threshold, it collapses into a black hole. In the beginning, all the mass in the universe was in close proximity. How could all that mass not trigger a black hole collapse? Surely there was more mass in the local area of the blast than exists in a black hole, and light (a massless particle) is a lot harder to suppress than actual mass. Therefore, it should have been impossible for any matter to have escaped the Big Bang (?!). What am I missing... EDIT: Front page! Thanks reddit! The Big Bang singularity isn't the same as a black hole. A black hole is a point in space time with infinite curvature. The Big Bang singularity was the entirety of space time. And the entirety of space time expanded. That being said. We have no working theory of black holes or the Big Bang. We just see that our models asymptotically reach these points. We can't explain what actually happens at these points, though.
How long does it take a virus (such as Covid-19) to reproduce from the moment it enters a cell? How fast is viral reproduction on the level a single virus? Once it enters a cell, how long does it take for it to take over the cell, create more viruses and burst forth from the host cell? Does time vary significantly from virus to virus? Are ones with shorter time generally more dangerous/infectious? A complete viral replication cycle includes: -Cell entry -Unpackaging of genome and proteins -Genome replication and protein synthesis -Assembly of virions -Release of virions from the host cell The time required will vary quite a bit from virus to virus. Generally positive-sense RNA viruses (for example, coronavirus) are faster since their genomes can be directly translated into protein. For the SARS coronavirus this takes between 7 and 24 hours: https://www.ncbi.nlm.nih.gov/pubmed/15170625 For SARS-CoV-2 it's more than 6 but less than 12 hours: https://wwwnc.cdc.gov/eid/article/26/6/20-0516-f4 Influenza virus is one of the fastest replicating, with a replication cycle of around 6 hours: http://www.euro.who.int/en/health-topics/communicable-diseases/influenza/data-and-statistics/virology-of-human-influenza Herpes simplex virus 1 and 2 also have replication cycles of around the same time (hours). For cytomegalovirus (aka human herpesvirus 5), it's around a day or two (source: https://www.ncbi.nlm.nih.gov/books/NBK8157/ ) Keep in mind that one infected cell can produce thousands of virions, so that even if it takes ~6 hours to produce them, the end result is extremely rapid replication.
What would happen if two stars merged together? In some cases a nova or supernova would result. Some recent papers proposed for example the element gold could only be synthesized from the collision and merger of two neutron stars. Assuming some stars with considerable nuclear fuel remaining/time on the main sequence, there would be fairly massive explosion/outbursts from disruption of both stars structure before the combined mass reassembled into a new star. An event observed in 2008 is believed to be the first direct observation of a stellar merger . The paper makes reference to another astronomical object V838 Monocerotis . One theory is this is the remnant nebula from the explosion and combined star from a stellar merger.
Do rooms with hard reflective walls (such as a bathroom) leak less sound? I've recently been practicing my ukulele late at night in my apartment, and have wondered lately whether practicing in my bathroom (with its hard reflective walls) will leak less noise than playing in my living room. If I can hear myself more loudly inside, does that mean that outside the room there is less noise leaked? Depends on what you are comparing it to, but all else being equal: yes. If I have two closed rooms, one with hard tile walls and the other with sound-permeable drywall, less sound is going to leak from the tile wall room. However, this assumes that all the sound is going through the walls. In truth, you have different paths that sound can take. For example, sound might travel through a window, through an open doorway, through a closed door, through the structure of the house, etc. In this situation, the fact that the sound is reverberating longer in the tile room might actually hurt you. So, it's all going to depend on which paths for sound are most important. For a ukelele, which is fairly high frequency, the door will block a lot of the sound. For a tuba, it probably wouldn't do much. My suggestion is to get a sound level app for your phone (you don't need something great, just good enough to do relative levels) and test the sound level yourself. If you do this, I'm curious to see what you find! Try playing with the door open, vs closed. Then try taking all the towels/rugs out of the room (since they absorb sound) and pulling the shower curtain.Then make a comparison with some other room.
While sleeping, if nothing from the outside world triggers our wake-up, what most commonly triggers it? For instance, does something just sort of trigger in our brain and tell us it's time to wake up? Thanks First, it should be noted that sleep is not a continuous block. Even without any environmental stimuli, spontaneous awakenings are common during the night. For a healthy adult, it is typical to wake briefly about 20 times per night, with increasing frequency towards the end of the night. You don't remember most of these awakenings because short term memory does not function normally during sleep or shortly after awakening. With that out of the way, I'll take your question to mean: What determines when we finally get up and start our day? The answer is that there are regions of the brain involved in controlling the overall arousal state of the brain (specifically, the ascending arousal system in the brainstem, and some neuronal populations in the hypothalamus and basal forebrain). The activity of these regions is primarily determined by two underlying processes: . We all contain a clock with a period close to 24 hours. This clock resides in a group of neurons in the suprachiasmatic nucleus of the hypothalamus. The clock promotes arousal during the circadian day and promotes sleep during the circadian night. Towards the end of the night, there is a progressively increasing arousal signal being sent from this clock. . While you are awake, certain substances build up in your brain, including adenosine, cytokines, and prostaglandin D_2. These substances make you feel more sleepy. During sleep, these substances are cleared from the brain. Towards the end of the night, the clearance of these substances results in an increasing drive to awaken.
Do learned behaviors have an effect on evolution? For example, there are pods (?) of dolphins that have learned special methods of hunting fish, like stirring up mud to trap the fish against the surface. The dolphins teach their offspring this method, increasing the chances of their offspring surviving because of this superior hunting method. It seems to me that even if a dolphin weren't particularly fast or healthy, it could still survive because of this "smart" hunting. Some species of monkey have also learned to use tools to open nuts/fruit, which is another behavior that is passed on through nurturing. Another (extreme) example would be humans and modern medicine. Have we "beaten" evolution because we can cure the people who otherwise would have died from Chicken Pox, etc.? While learned behaviors certainly influence evolution, it is important to remember that the specific learned behaviors themselves are not being passed on via evolution, and that there is a cost to learning. Nobody 'beats' evolution, but what exactly is under selection can change. What you're talking about in most of these cases is cultural transmission (of information) as opposed to the transmission of genetic information. The difference between these types of information sharing is that as soon as you take an individual out of the social environment and raise it somewhere else, the advantage of learning is gone. Ie, if you took a human and raised them without ever letting them interact with another human being, they lose the benefit of all the accumulated knowledge. What learned behaviors can do is change the selection individuals experience. In your dolphin example, learning to hunt by stirring up mud might reduce selection on swimming speed by reducing the need to chase fast prey, but it might increase selection on visual acuity (ie, to see prey in muddy water). It might also select on increased learning capacity, so that individuals who learn new hunting methods more quickly can start catching prey at an earlier age or with less practice. It's important to remember that increased learning doesn't come for free. Learning comes at the cost of time (using one of your examples, just think about the amount of time it takes to comprehend modern medicine..) and the cost of making mistakes before the behavior is perfected. They also have a physiological cost of increased brain size, which can feed back into increased gestation and development time, which then reduces the number of children a parent can successfully raise. In some cases it's worth the cost, but in many cases it's not.
Why is northern Alaska and Canada pockmarked with "lakes"? I was looking over google maps when I noticed that northern Alaska and Canada had these dense "lake" formations. What are these from and why do they form that way? For example: I have been waiting for a geology themed question for AGES! The answer to this is glaciers! During the last ice age massive multi-km thick sheets of ice covered canada, alaska and some northern parts of the lower 48. Think Antarctica, but in Canada! These super thick sheets of ice move very slowly, but over thousands of years these sheets scour every single feature off the surface. The glaciers plane off the hills and later fill the valleys with gravel (or till). So how do these lakes form? Well, if you've planed off your entire landscape, you've destroyed your entire hydrologic network- the streams and rivers that carried water away are gone, and the water is stagnant. This is why Canada is covered with countless small shallow lakes. Over time, the lakes will fill in with sediment and streams will return. Eventually, it will look something like what northern indiana or iowa look like now. This explains what areas like quebec look like . Curiously, the exact location you pointed out is a different kind of landform, called kame and kettle topography. To understand the difference between the area that you picked and the area that I linked in this post, compare the shape and pattern of the lakes. In Quebec the lakes are irregular, somewhat interconnected, and lie directly on the bedrock. In the spot you selected in alaska, the lakes are round, seem to follow a preferential direction and seem to lie on glacial gravels or soft sediment. These lakes are different! So how do glaciers work into this? Well it turns out that glaciers effect the landscape in different ways depending if you are near the start or end of a glacier. The beginning of a glacier is erosional, the glacier isn't carrying a lot of sediment yet and it carves deeply into the rock beneath it. The beginnings of glaciers form landscapes like in Quebec or northern minnesota. The ends of glaciers are totally different. By the time you get to the end of a glacier, it is carrying all the sediment picked up from the glacier gouging out the ground upflow. At this point the glacier is melting away, and as it melts it begins to become dirtier and dirtier and starts to turn into a pile of rocks. Check out this glacier in alaska. See how it grades from a pure white snow to dirty and vegetation covered! As the glacier melts, big pockets of ice can be trapped under the sediment. As the glacier retreats, it leaves big blocks of ice buried beneath the sand and boulders. Over time these blocks melt away and the cavity where the ice was collapses, forming a small lake. These small, round lakes are called and form near the terminus of glaciers. These are the lakes you saw in alaska. So the td;lr here is that these lakes were made by glaciers during the last ice age. The particular ones you pointed to are a type of glacial lake called a kettle.
Is there any material that has a different melting and freezing point? i.e. is there any material that will tend to "stick" to whatever state it was in, whether that was solid or liquid, for some period? I know that there are other reasons that all snow doesn't melt as soon as it gets above 0 degrees (it takes time for heat to transfer, different specific heats of air vs. water, "above 0 degrees" on the weather doesn't account for shade vs. sun, etc.). But is there any substance where you can take a solid sample and a liquid sample, bring them into an environment with precisely the same conditions, and have them remain, respectively, solid and liquid? What about gas and liquid? I know that water vapor, liquid, and ice can continue to exist in the same room for a while, but again because of varying conditions... but I'm wondering if there's a further stickiness. Basically, a material that turns solid when it gets to temperature/pressure/etc. conditions X, but won't turn back into liquid again until it gets to X + 5 degrees, leaving a window where both states are stable. I hope I've explained my wondering sufficiently... What you're describing sounds like hysteresis , in which the state of a substance depends not only on current environment but also on prior environment. The example wikipedia lists is agar , which melts at 85C but freezes at 40C. Other ' antifreeze proteins ' and nonprotein macromolcules also exhibit this effect. More info here. edit: see EagleFalconn's and coniform's posts below, as they are more accurate than mine.
Why do rotating black holes look so weird? So I found website from ESA where you can play around with a black hole and the rotating black hole (Kerr black hole) looks so weird. Why does it have that shape? It's because of an effect called 'frame dragging': The spin of the black whole twists the spacetime with it. This means that trajectories of light look very different when orbiting the black hole clockwise in contrast to orbiting it counterclockwise. They are 'dragged' by the rotation. For an outside viewer, this distorts light coming from behind the black hole differently, depending on wether it passes the black hole on the left or the right. edit: If you are talking about , the reason why this actually looks rather weird is because the gravitational field is much more complex. "With hair" is a bit of an inside joke, but refers to the fact that there's additional physical features on the outside of the black hole. In this case, there's a matter field swirling around the black hole, forming an equilibrium with the hole itself. In the image on ESA's site you can't actually the matter, only the gravitational lensing by it. The reason that you can't see the matter is that it's only an rather abstract mathematical model of matter, a . It's not defined what makes up this matter, if it could interact with light at all and so on. So for now let's assume it's transparent. This black hole / matter combination has a more complicated gravitational field than an ordinary kerr hole, which can lead to chaotic orbits. You can still see that it's a spinning system, because it looks different on the left side than on the right side. But additionally there is some complex warping going on. The reason for this is, that the effective potential for the photons (considering all like gravity, centrifugal force etc.) forms intricate pockets, in which the photons can get trapped for a while. They'll bounce around in these pockets, eventually leaving in an arbitrary direction, which is extremely sensitive to the initial angle at which the photon approached the black hole. It's very similar to the fractal pattern you see when looking at the reflections of four spheres , which is also a chaotic motion. You can try this for yourself with christmas tree balls . The orbits of photons are not reflected by mirror walls, but are bouncing off potential wells, which leads to the highly chaotic regions you see in the images. There's a detailled study of these effects in this paper , if you want to read more. The traps / pockets are visualized on page 20 for example.
is there a name for ability to control the shape of the crystalline lens in humans, and is it common? I am able to blur my own vision by moving a part of my eye, that I assume is my crystalline lens. I'm able to control this consciously, as I would tense a muscle. I've never been able to find any evidence of this in another human. Your cornea is the external "bump" of the eye that lies above the iris and the lens. It is fixed and does not change in focus, though it can become occluded or scratched by things getting in your eye. The lens of the eye is comprised of layers of transparent, interlocking cells that are individually rigid bit collectively flexible. The muscles attached to your eyeballs are responsible for the overall movements of the eye but ALSO for flexing the lens, a process known as "accommodation." This flexing allows for rapid adjustment of the focal length of the eye and enables you to quickly switch from far to near objects. It also allows you to deliberately unfocus your eyes to make your vision blurry. That you can willfully do so displays good control over you accommodative vision.
How do we calculate rates of change mathematically knowing what we do about quantum mechanics? The obvious example is current. We know charge is a discrete value, so we can't use basic calculus to find the rate of change of charge as the derivative which, as I know it, can only be done on a continuous function. In many applications, we may simply assume that the charge can take arbitrary values, and this is usually a good approximation. For instance, in a wire, the elementary charge is negligibly small compared to the total charge in some cross-section of the wire. Precisely, in any cross-section, the charge is , where is some integer and is the elementary charge. The value of is so small compared to (or is so large compared to 1) that the difference in charge between neighboring cross-sections is proportionately small as well. So we can approximate the charge as a continuous function of the position along the wire. This type of approximation is done in other fields as well. For instance, in fluid mechanics, we know that the actual molecules are discrete and there can only be so many in a given volume (there may even be none). But for almost all applications we can approximate the fluid as a continuum. Typically, this means that the intermolecular distance is small compared to the characteristic length scale of the problem. There are some notorious examples where this approximation breaks down. For instance, for strong shock waves in some gases, the length scale of the shock (where the rapid change in density or velocity is) may be on the scale of the mean free path of the gas molecules. In that case, the continuum approximation breaks down and a kinetic theory may be more appropriate. In plasmas, the intermolecular distance may be very large, but the continuum approximation may nevertheless still be good. There are other factors at play, like the relative strength of the self-electric, self-magnetic, and external magnetic fields, for instance, that may enter the scales of the problem in such a way to make fluid-like equations still a rather good approximation. But for general applications, I would say plasmas more often break the continuum approximation than traditional fluids, in that a full kinetic theory is more often required for plasmas than fluids.
Does the universe have total angular momentum different from zero? Is the total angular momentum if the universe zero? If not, wouldn't this determine a privileged direction in space? You can set up polar cosmological coordinates (FLRW basically) and in fact do compute said angular momentum with respect to some origin (say, Earth). It turns out to average to zero above the supercluster scale. If it wasn't so, you wouldn't have an isotropic Universe in those same coordinates, but you actually do. Fun fact: as opposed to energy, total angular momentum is conserved in our Universe.
I was recently told that loss of antarctic ice was causing changes in the gravity of earth, how is this possible? if gravity is based on mass how can melting ice reduce the reduce the mass of earth? It's not changing the mass of the Earth, it's changing the mass distribution. If you look at gravity maps of the Earth , it's not perfectly uniform everywhere because the mass of the Earth is not spread out perfectly equally. Melting large amounts of ice basically redistributes mass from that area to other places, which can be measured by very precise maps of the gravitational pull everywhere on the planet. Edit: The total mass of the Earth doesn't change, and the gravity of the Earth would still look the same from a large distance when it basically acts like a point particle, but when you're up close on the surface, moving the mass around can change the local gravity.
Why do we panic? I understand the fight or flight response, but panic seems to be somewhere in the middle and tends to cripple most people like a deer in headlights. All rational thought seems to go out the door.. Why? Not wanting to excite a predator has got to be at the top of the list of reasons, but there are other instances it can be useful. You freezing up in a dangerous situation might keep you from making a situation worse, or injuring yourself further. In a group scenario, having everyone running in all directions with different ideas would be chaotic. Freezing and waiting for the emergence of a single to few leaders to direct the rest would likely be safer and provide more of a chance of remaining together for the group.
How do our immune systems know not to attack healthy bacteria? I'm assuming it's some sort of chemical signal secreted by the bacteria, but what's the exact mechanism? According to Wikipedia there are 1 quadrillion bacteria in the gut. That's 10 times the number of cells in the body. So even if the immune system was going to, I don't believe it would be successful. But there is information on how the immune system interacts with these bacteria . One of the functions of the protective flora is to train the immune system to recognize other bacteria in more harmful locations of the organism. Also this article gives some information on how the two systems interact, but you need a little immune physiology knowledge before reading it. Also, this is a study done on mice proving that the flora is there to train your immune system for other pathogens that it will encounter.
How is it that Jupiter can keep earth safe when they orbit the sun differently? 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.)
What causes stars to switch from Hydrogen fusion to using heavier elements? 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.
Is there a reason why radio towers aren't used for wifi? 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.
How are we affected by the speed of our travel through the universe? 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.
What would a pipe organ sound like on planets with wildly different atmospheres than Earth's? 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.
What's the highest frequency laser? 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.
Does the moon have a mantle? 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
Nocturnal Dinosaurs, evidence and how common? 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/
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? 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.
Is there a limit to how loud a sound can be? 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.
What is actually going on with new COVID-19 variants and their mortality rate? 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.
Considering that a mirror changes the direction of photons, is it actually "deformed" or even "used up" in the process? 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).
Can you absorb nutrients through the colon? 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.
can a butane lighter increase the temperature of aluminum to its heat of vaporisation? 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.
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? 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.
Need help translating Chinese publication. side note: chinese using HIV/AIDS in research!? 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!
Are spiders immune to getting stuck in their own webs? 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.
What determines the angle, length and curvature of a rainbow? 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.
Can an isotope have a negative number of neutrons? 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.
I'm reading about mu-metals and I had this question... 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.
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? 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!
Does light travel forever? 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.
Why does my pulse feel "stronger" on an area of my body that I recently injured? 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.
My seven-year-old would like to know if gels have a "skin" (meniscus) like water does? 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. If 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.
Are hive insects incestuous? If so, how do they deal with inbreeding? 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.
Why does an infinitely-powered, constant-thrust spaceship never reach 300km/s? 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.
Does hot food provide more energy than cold food? 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.
Why do computers sometimes move slowly? 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.
When losing weight, how does the body choose where to pull fat from? 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.
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? 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.
AskScience, what part of Earth has the smallest average temperature range? What part has the most hospitable temperature range? 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.
Is it possible to measure a liquids specific gravity in space? 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.
How do radio stations know how many receivers are listening to them? 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.
Why do electrons have a "negative" charge? 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.
How can locks (as in door locks) or anything that requires a unique part be mass produced? 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 .
If you're travelling at 0.99c, would you still observe light moving away from you at c? 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.
Why don't batteries get drained instantly when shorted? 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.
How fast is the earth moving in relation to the center of the galaxy? Does that speed vary? 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
How exactly does histamine improve tourettes? 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. It 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. If 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). Hope this helps, feel free to ask follow ups
Is E=MC² just a logical extension of F=MA with a different definition of terms based on discoveries unknown to Newton? ... 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
Does the asthenosphere actually exist? 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 .
Do you have any stories about interesting/promising experiments that worked in the lab but not in the real world? 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.
Could you theoretically use the DNA from two sperms or two eggs to clone/create a human being? 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).
Do plants have stem cells and do they recombine their genes? 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.
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? 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.
Can you (roughly) determine the dosage of a drug taken based off of the blood concentration? 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.
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 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.
Why does a liquid having zero viscosity allow it to climb up and out of containers? 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.
Can photons be counted? 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.
Do people in wheelchairs suffer from deep vein thrombosis more often than other people? 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.
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? 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.
Is there any difference between -1G, and being upside down? 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.
If the Apollo program had continuousely failed, how much longer would it have taken the Russians to get a man to the moon? 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
What would I see with the naked eye if I was half-way to Andromeda? 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.
Is the size of DNA proportional to the complexity of the organism? 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.
How long will the astronaut's footprints on the moon really last? 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 ;-)
How "mobile" are bacteria and viruses on dry skin? 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. :)
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? 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.
Are solar panels as effective on mars, further from the sun, and with less atmosphere? 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
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? 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 (See upper left graph in figure 2)
Are these lights safe to use? 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.