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DontMockMySmock posted:You don't have to think about it as a two-dimensional sheet expanding in three dimensions. Instead a better picture would be this: extend your piece of paper to infinity in all directions. Draw a grid of dots on it. Now, stretch it by a factor of two, so that the distance between each dot and its neighbor doubles. THAT is a good picture of what the expansion of the universe is like, and you never needed to think about the third dimension. It's also easy to extend to three dimensions without having to think four-dimensionally: just make it a 3D grid throughout all space, and expand that. That is what the expansion of space is like. The math to describe this is actually pretty simple once you know a little bit of relativity. Yeah, this is fine - but the issue I have is that our infinite sheet of paper means that our universe is infinite, whereas my understanding is that the observation from the Big Bang shows that there is a boundary, albeit one that is receding from all points equally? EDIT: Hmm, if we have our 2 dimensional universe on the surface of a balloon, then there is no boundary, and I can see that, in the confines of 2 dimensions, each point recedes from each other point fine. But as an infinite sheet, doesn't that imply that our universe was always infinite? Argh o.m. 94 fucked around with this message at 10:02 on Sep 21, 2010 |
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Sep 21, 2010 09:59
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SanitysEdge posted:You could do something like this, but the energy it would take to spin it up to the point where it could slingshot spaceships would be equal to the rest-mass-energy you are trying to emulate, mc^2. And since c is a pretty big number, and the mass we want is a pretty big number (comparable to a planet, call it an Earth mass). . . . yeah that's four times as much energy as the sun will radiate over its ENTIRE LIFETIME. It'd be a heckuvalot easier to just tow a planet to where you needed it! Derpes Simplex posted:My understanding is that faster-than-light travel may not necessarily be possible, but recent experiments have implied that faster-than-light information transmission is possible - the experiments having to do with transmitting quantum spin over distances of several kilometers, if I remember correctly. How groundbreaking are those experiments and/or what are their implications? So, entanglement. This gets talked about a lot in popular science. The key point to the matter is this: information, energy, momentum, mass, charge, angular momentum, or anything else that is physically observable cannot travel faster than light. In the collapse of an entangled wave function, something travels faster than light but it carries no real information. Basically these experiments work by having two particles interact, then move far apart without interacting with anything else, and then measuring them both and comparing the results. Here's a simplified setup: you have two (hypothetical) quantum "coins" that are entangled, brought far apart, and flipped. If coin A flips heads, B will always flip tails, and vice versa. This is repeated a bunch of times. So Alice takes coins A and Bob takes coins B and they do the experiment. If Alice flips her coin, Bob's will be then determined to be the other side with 100% probability. If she doesn't, Bob's coin is 50/50. But either way, without comparing notes, Bob won't notice any difference because his coin is 50/50 either way, either "naturally" when Alice doesn't interfere, or through the entanglement because Alice's coin is also 50/50. The key point is that any patterns that may arise are not apparent until both experiments communicate with one another at the speed of light or slower. Then Alice and Bob can look at the data and say, "Ah, my flipping of coin A must have caused coin B to behave in this way," but you can't actually tell that it did so without some other subluminal communication between Alice and Bob. Hyper-Urho-Kekkonen posted:Is it accurate to say that the existence of quantum indeterminacy demonstrates that the law of mass/energy conservation does not actually apply at the quantum level (regardless of whether or not we can actually use that fact to get free zero-point energy or whatnot)? In the world of quantum mechanics, conservation laws are something that applies to "average" or expectation values. The expected energy is conserved, the expected momentum is conserved, and so on. totalnewbie posted:Ion drive as a plausible means for space travel over extremely long distances? I am no expert on space travel, but there's nothing wrong with ion thrusters as a means of travel. It may, in the long run, be less desirable than other means that don't require carrying boost mass, such as magnetic scoop-ramjets (which would scoop up interstellar dust and thrust it backward with magnetic fields) or solar sails (which use radiation pressure as a source of momentum). But it's certainly better on the long term than chemical fuel. Chemical fuel is fine for the solar system, but pretty soon most of your fuel is spent pushing the rest of your fuel around, and most of THAT fuel is spent pushing the rest of that fuel around, and so on. Traveling close to c is hard. The faster you go, the harder it is to accelerate. That's really the only problem with it. I already answered about entanglement in this post. That's a big "no" on that one. General relativity is a tough thing to study because only in the most basic cases can you find an exact, analytical solution. And when you try to come up with a numerical solution, it gets complicated REALLY fast. So most research in general relativity involves using powerful computers to do numerical simulations of interesting situations, like binary black holes, binary neutron stars, black hole collisions, core-collapse supernovae, rotating neutron stars, and things like that. I work on stuff like that. oiseaux morts 1994 posted:Yeah, this is fine - but the issue I have is that our infinite sheet of paper means that our universe is infinite, whereas my understanding is that the observation from the Big Bang shows that there is a boundary, albeit one that is receding from all points equally? There is a "boundary" of sorts, but it's not like you're imagining it. Thanks to our being limited to the speed of light, there are things that are so distant that we can't ever see them (they are further from us than the speed of light times the age of the universe). The "observable universe," then, is confined to a particular shape based on the speed of light and the expansion of the universe. There are things (or maybe they don't exist, and we can never know) that are far enough away that we can't see them. Maybe the universe is spatially infinite; that's the model that is generally used in cosmology (since it's the simplest). Maybe there's a boundary out there somewhere. Maybe eventually we'll find the edge of the universe, look out, and see Cowboy Universe versions of us staring back. Who knows? Whether or not there is a boundary doesn't really affect your conception of the expansion of the universe - if there is a boundary, it is expanding away from everything else also. It's a much easier to depict thing, too - your sheet of paper is just getting bigger. I like the infinite picture better, but maybe that's just my point of view.
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Sep 21, 2010 10:51
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Seriously though, can you please elaborate on what the field of "general relativity" entails?
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Thanks. Here's another question. As I understand, quark stars are still theoretical. Obviously, if they existed, they would exist somewhere between a neutron star and a black hole. Approximately how large is the range of stability (or however you might describe it) for such a star (in terms of mass, I suppose).
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Sep 21, 2010 11:56
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DontMockMySmock posted:There is a "boundary" of sorts, but it's not like you're imagining it. Thanks to our being limited to the speed of light, there are things that are so distant that we can't ever see them (they are further from us than the speed of light times the age of the universe). The "observable universe," then, is confined to a particular shape based on the speed of light and the expansion of the universe. There are things (or maybe they don't exist, and we can never know) that are far enough away that we can't see them. Maybe the universe is spatially infinite; that's the model that is generally used in cosmology (since it's the simplest). Maybe there's a boundary out there somewhere. Maybe eventually we'll find the edge of the universe, look out, and see Cowboy Universe versions of us staring back. Who knows? So a way of looking at it perhaps is that the points in our flat, infinite sheet are constrained within a circle of expanding radius - points outside this circle are unobservable, and we consider the boundary of our universe to be this circle, which is expanding with the points inside. However, does this mean that this "circle of observance" covers a different area of space dependant on the point of origin (observer)?
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Sep 21, 2010 12:10
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The following questions may be somewhat meaningless, but the concepts baffle me. Why is the principle of least action true? Why is it that light "wants" to travel in the shortest possible time? Why do atoms try to achieve the lowest possible energy level? Also, you said you worked on general relativity. I know next to nothing about these things but I remember reading A Brief History of Time by Hawkings and he talked about reconciling the ideas of general relativity and quantum mechanics. How is that effort progressing? It's been decades since that book so I'm sure I've missed a lot of stuff that happened since then. Cool thread!
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Sep 21, 2010 15:46
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I recall reading in Brian Greene's "The Fabric of the Cosmos" that some physicists believe there may be something more fundamental than time and space. What are your thoughts on timeless physics, and in particular, the ideas in "The End of Time" by Julian Barbour? Do you think that the Andromeda paradox proves that free will can't exist? Care to explain the holographic principle and cosmic censorship (no naked singularities) in layman's terms? Lastly, I think I've read that the "delayed choice quantum eraser" experiment seems to imply that our actions in the present can affect the past. Is this or is this not the case?
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Sep 21, 2010 17:41
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totalnewbie posted:Thanks. Here's another question. As I understand, quark stars are still theoretical. Obviously, if they existed, they would exist somewhere between a neutron star and a black hole. Approximately how large is the range of stability (or however you might describe it) for such a star (in terms of mass, I suppose). "Quark stars" are not some entity separate from neutron stars, they are just a possible form of neutron stars. These days, most people think that neutron stars have a crust of ordinary degenerate neutron matter and a core of quark-gluon plasma. But we can't be sure. Nothing is really known about quark-gluon plasma. The strong nuclear force manages to be pretty ineffable, for all we've studied it, so there's not a whole lot of theory to go on. There isn't any experimental data either, although there are people at the Relativistic Heavy Ion Collider who are doing their best to get some. oiseaux morts 1994 posted:So a way of looking at it perhaps is that the points in our flat, infinite sheet are constrained within a circle of expanding radius - points outside this circle are unobservable, and we consider the boundary of our universe to be this circle, which is expanding with the points inside. Yep. tourgon posted:The following questions may be somewhat meaningless, but the concepts baffle me. The principle of least action works. Don't ask me why! It's just as useful as asking why Coulomb's electric force law is true, or any other similar question. It's pretty much a religious question, and I can't really give you an answer. That's just the way the universe is! Same with your next couple of questions. As for the reconciliation of QM and GR: there has been basically zero progress! There are different candidate theories, but none of them are really testable yet. The LHC may begin to give us an insight into this problem, but unlikely. The problem is that gravity is soooooo weak, and the new physics occurs at such incredibly high interaction energies (billions of billions times larger than the LHC collision energies, at LEAST), that it's basically impossible to test any theories of quantum gravity in the foreseeable future. Maybe in the distant future when we have a black hole we can examine up close and experiment with, we can learn something useful. Bodhi Tea posted:I recall reading in Brian Greene's "The Fabric of the Cosmos" that some physicists believe there may be something more fundamental than time and space. I haven't read "The Fabric of the Cosmos" or "The End of Time," but it sounds unphysical to me. If the universe is a series of "timeless instants" (as it's described on "The End of Time"'s wikipedia page), you would have a solid concept of simultaneity - which special relativity denies. Speaking of simultaneity, the "Andromeda paradox" isn't a paradox, and doesn't have anything to do with free will. It's a curious result of special relativity, sure, but thanks to the speed-of-light limitation it's entirely academic. Both the stationary and the moving observer agree on those things that they can both see (everything in both of their past light cones), once you take into account their difference of coordinate systems and thus their different concepts of time and space. The holographic principle is an idea that is a resolution of the black hole information paradox. The black hole information paradox is this: a black hole has only a few numbers that tell you everything about it: its position, mass, spin, charge, velocity, etc. But the stuff that falls into the black hole, being a composite of many different particles that all have their own positions, masses, spins, etc., has much more information than that. So when it falls into the black hole, where does that information go? When the black hole then emits particles in the form of Hawking radiation, where does the information for those particles come from? The black hole needs to be able to store information somehow. In some theories of quantum gravity, string theory in particular, you can resolve this because infalling matter imprints itself on the horizon of the black hole. This is the holographic principle. Cosmic censorship is still an open question. It's hard to formalize the definition of a "singularity" to make a proof one way or another. There exist valid solutions to general relativity that have naked singularities, but it's possible that these spacetimes are inaccessible from any reasonable initial conditions, and so there may be some sort of cosmic censorship principle that holds under certain conditions. The "delayed choice quantum eraser" experiment is another case of entanglement giving you astonishing results only after you assemble the information and look at it a certain way. Decoherence, the "collapse of the wavefunction," can happen in an acausal way, as this experiment does, but any information transfer is still causal. The trick in this one is that the interference pattern (or lack of one) in the "signal" photons can't be seen until you select the correct set of signal photons based on what their entangled "idler" photons did. So no real, unusual thing was observed in the first photon until information got to it, causally, from the other photon's detector. It's just the same as my earlier thought experiment where Alice and Bob compare notes and Alice remarks, "Astonishing! Every time I flipped heads, you flipped tails!" Bob couldn't possibly find any astonishing pattern until he compared notes with Alice and preferentially sorted his data based on Alice's data, a comparison which occurred according to the usual speed-of-light restriction. Exactly the same sort of thing is going on here. Of course, it's interesting that decoherence can travel back in time, but it shouldn't be surprising to anyone who knows their special relativity.
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Sep 21, 2010 19:13
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DontMockMySmock posted:Here's a simplified setup: you have two (hypothetical) quantum "coins" that are entangled, brought far apart, and flipped. If coin A flips heads, B will always flip tails, and vice versa. This is repeated a bunch of times. So Alice takes coins A and Bob takes coins B and they do the experiment. If Alice flips her coin, Bob's will be then determined to be the other side with 100% probability. If she doesn't, Bob's coin is 50/50. But either way, without comparing notes, Bob won't notice any difference because his coin is 50/50 either way, either "naturally" when Alice doesn't interfere, or through the entanglement because Alice's coin is also 50/50. The key point is that any patterns that may arise are not apparent until both experiments communicate with one another at the speed of light or slower. Then Alice and Bob can look at the data and say, "Ah, my flipping of coin A must have caused coin B to behave in this way," but you can't actually tell that it did so without some other subluminal communication between Alice and Bob. This is the best explanation of this phenomenon I've ever read, thanks for this. I'm about to start a 4 year Bsc course (complete with foundation year since I'm a filthy mature student whos forgotten how to count and add up and stuff) at the University of York, and as I prepare for it I'm looking to better understand how you relate the physics of an idea to the mathematics. In the case of stuff like "distance over time" its fairly obvious, and differentiating the data to yield speed/ second differential for acceleration I can understand and play with in my mind, but for more complex stuff like the oscillation of a spring, say, or the study of cavity radiation... is this something you develop over time or is an ability to conceive of the mathematics of the problem as you do the physics behind it simply something you "get" and no amount of study will change that?
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Sep 21, 2010 19:40
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Thanks for the response. Although I do think you're dismissal of Greene and Barbour is a bit hasty, I don't blame you since you are unfamiliar with either.
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Sep 21, 2010 19:49
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Gavrilo Princip posted:I'm about to start a 4 year Bsc course (complete with foundation year since I'm a filthy mature student whos forgotten how to count and add up and stuff) at the University of York, and as I prepare for it I'm looking to better understand how you relate the physics of an idea to the mathematics. In the case of stuff like "distance over time" its fairly obvious, and differentiating the data to yield speed/ second differential for acceleration I can understand and play with in my mind, but for more complex stuff like the oscillation of a spring, say, or the study of cavity radiation... is this something you develop over time or is an ability to conceive of the mathematics of the problem as you do the physics behind it simply something you "get" and no amount of study will change that? It's definitely something you develop over time. You need to have the mathematical background first, and then you can understand the equations involved in the appropriate physical contexts. For example, the oscillating spring obeys Hooke's law, F = -k x. It's completely natural for me to say "F = m a, and a = d2x/dt2, so this is a differential equation that looks like d2x/dt2 = - (k/m) x, and this obviously has the general solution x = A sin(wt) + B cos(wt) where w = (k/m)1/2." It hardly requires any thinking at all, any more. But that's only because I've studied oscillating systems so much that it's become second nature. Back before I knew anything about differential equations, Newton's second law, or that acceleration is the second time derivative of position, this wouldn't have been obvious to me. The first time it was shown to me that sines and cosines are solutions of Hooke's law, I was like "  ". I was just learning calculus at the time, so it was like an amazing revelation. I never could have come up with it on my own. As for cavity radiation, well, that's quite a bit more mathematically intense, and you really need to understand Fourier analysis before you dive into it. I hardly know anything about cavity radiation, personally, because it doesn't interest me, but Fourier analysis is like an old friend, thanks to lots and lots of practice. Bodhi Tea posted:Thanks for the response. Although I do think you're dismissal of Greene and Barbour is a bit hasty, I don't blame you since you are unfamiliar with either. When you are a physicist, it's easy to flippantly dismiss these sorts of philosophical theories. But there's a good reason for that. Physicists should always be concerned with reality, and a theory is not real until it puts forth a testable prediction, and Green's and Barbour's theories of timelessness don't seem to me like they could ever give you a testable prediction. Of course, maybe they can, and maybe they're right, and maybe someday there will be a cover of Nature that states in bold type "Time doesn't exist" under Greene's and Barbour's smiling faces. And then I'll look like an rear end. But for every crazy guy who turns out to be right, there are thousands of crazy guys who are so incredibly wrong.
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Sep 21, 2010 20:06
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Sorry for the cosmology questions. If the Universe is infinite outside of our observable Universe, do you think it is possible for it to have infinite matter? This comes up a lot in cosmology and I don't understand how there could be infinite matter. edit: Actually now that I consider our limited understanding of singularities and associating an infinite density with it I can picture an infinite amount of matter. It's just a question now if inflation separated our observable Universe from the rest of it. Maybe you have something more to this. Woke Mind Virus fucked around with this message at 20:32 on Sep 21, 2010 |
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Sep 21, 2010 20:27
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Thanks for the advice, I'm definitely looking forwards to it a lot more now that I understand what's required of me. Maths is so poorly taught in school, and what they do teach is inherently platonic in nature with no indication of how it applies to real world situations beyond cursory approximations of situations such as "Jake is stood at point x a meters from y, which is b number of meters below point z. Determine the angle at point x" in a perverse attempt to use real world situations to teach platonic concepts rather than the other way round. Actual physics lessons weren't much good either since beyond some basic trig for determining light refraction as light enters a substance of different density, and some algebraic transposition for stuff like distance over time and the like most lessons were decidedly light on the maths and focused largely on teaching disinterested students what the forms of energy are. (Also second question, am I right in thinking that fermions all have half-integer spin like the 1/2 spin of the electron and bosons all have full-integer spin, and if so to what degree does the spin dictate their behaviour if at all. Thanks)
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Sep 21, 2010 20:59
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synapse posted:Sorry for the cosmology questions. If the Universe is infinite outside of our observable Universe, do you think it is possible for it to have infinite matter? This comes up a lot in cosmology and I don't understand how there could be infinite matter. There's no need to apologize, that's what this thread is for. Since, on very large scales, matter is distributed pretty evenly in the universe, an infinite universe would seem to imply infinite matter. But it doesn't matter; anything outside the observable universe can't possibly affect us, so there's not a whole lot of point thinking about it. Now seems like a good time to talk about light cones. So, information only travels at the speed of light or slower. So, we can only see something if the line connecting that event and us has a slope less than the speed of light, and it's in our past. Similarly, we can only influence something if the line connecting us to that event has a slope less than the speed of light. The set of events that match this criterion is called the "light cone."  In this diagram, one of the dimensions of space has been removed to make visualizing it easier. The surface of the light cone is the path that light would take radiating to or from us, and everything closer to us than that, inside the cone, is causally accessible. We say these points have a "timelike separation" from us, and that points outside the light cone have a "spacelike separation" from us (with the points on the cone itself having a "lightlike separation"). Two points with a spacelike separation are causally disconnected - neither can influence the other. Keep in mind that by "point," here, I mean an "event," a particular place and time. Now, you may know that gravity can bend light. So as soon as you have a spacetime with anything in it, gravity distorts your spacetime, and consequently the shape of your light cone. For example, within the event horizon of the black hole, the light cone at any given point has its future pointing entirely toward the center - if you're falling in past the horizon, your future necessarily becomes the center of the black hole, as a consequence of general relativity. This is all relevant to the cosmology. As the universe expands in the way it does over its history, it affects our past light cone. What we see when we point any sort of telescope to the sky is something that is on the surface of our past light cone, as it is in the instant we make the observation (since we are observing via light or other things that travel at the speed of light). Any object we look at, we are seeing just one point or one small portion of its existence - the point where its "worldline" intersects our light cone (a "worldline" is the path an object traces out through spacetime). Only those parts of its worldline that are within our light cone could possibly affect us. But its worldline continues on all the same. So an object may affect us, and then in its future, continue to exist beyond our light cone. When it comes to the very early universe, there were parts of the universe that affected our observable universe, but after the epoch of inflation (if such a thing exists) became no longer causually connected. Their worldlines wandered out of our light cone. Phew! It's hard to get your head around all this stuff, and hard to explain in words, but I wanted you to understand what you were suggesting with the phrase "inflation separated our observable Universe from the rest of it". Gavrilo Princip posted:Thanks for the advice, I'm definitely looking forwards to it a lot more now that I understand what's required of me. Maths is so poorly taught in school, and what they do teach is inherently platonic in nature with no indication of how it applies to real world situations beyond cursory approximations of situations such as "Jake is stood at point x a meters from y, which is b number of meters below point z. Determine the angle at point x" in a perverse attempt to use real world situations to teach platonic concepts rather than the other way round. Actual physics lessons weren't much good either since beyond some basic trig for determining light refraction as light enters a substance of different density, and some algebraic transposition for stuff like distance over time and the like most lessons were decidedly light on the maths and focused largely on teaching disinterested students what the forms of energy are. A lot of it depends on the quality of your math and science teachers, unfortunately. It can't be stressed too much how amazing it is that such abstract mathematical concepts as derivatives and complex numbers can be used to predict the future through basic, simple mathematical laws. Gavrilo Princip posted:(Also second question, am I right in thinking that fermions all have half-integer spin like the 1/2 spin of the electron and bosons all have full-integer spin, and if so to what degree does the spin dictate their behaviour if at all. Thanks) You have just stated the "spin-statistics theorem." Fermions are characterized by obeying the Pauli exclusion principle (no two fermions can occupy an identical quantum state) while bosons are unaffected. Fermions thus obey "Fermi-Dirac" statistical mechanics and bosons obey "Bose-Einstein" statistical mechanics. For complicated mathematical reasons that have to do with special relativity as it relates to quantum mechanics, all particles with half integer spin (1/2, 3/2, 5/2, etc) are fermions and all particles with integer spin (0, 1, 2, etc) are bosons. Personally, I understand the proof of the spin-statistics theorem for spin 1/2 and spin 0, but I've never been able to understand how they generalize it to all spins, nor do I have any desire to learn enough quantum field theory to achieve that understanding. It's all very technical anyway. So you'll have to take my word for it that the spin-statistics theorem is true. So besides quantum effects, the spin of particles can affect their macroscopic, classical behavior via the spin-statistics theorem. For example, at very very low temperatures, a gas of fermions becomes a degenerate gas, with the Pauli exclusion principle forcing particles into higher energy levels so that they don't occupy the same state as other particles in the lower ones. But a gas of bosons just all drops down to the lowest energy level, a state called "Bose-Einstein condensate." At moderate-to-low temperatures, the differences are more subtle, and at high temperatures they become less and less distinguishable from each other and less distinguishable from "Maxwell-Boltzmann statistics," which is the classical picture of statistical mechanics with no quantum effects at all. On a quantum level, whether particles are bosons or fermions is pretty important. If you have two identical particles described by an overall wave function psi(x1, x2), if they're bosons, psi(x2, x1) = psi(x1, x2), or in other words, swapping one for the other doesn't affect the wave function. If they're fermions, psi(x2, x1) = - psi(x1, x2), or in other words, swapping one for the other causes the wave function to change sign. The consequences of this are pretty subtle.
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Sep 21, 2010 21:35
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Thanks! I've been looking for a simple-er explanation for Bose-Einstein condensates for a while. Doesn't the same thing happen with supercooled helium effectively behaving like bosons at ultra low temperatures? I vaguely remember something about it from a book or periodical or something, effectively quantum behaviour on a visible scale (for example, stir it and it doesn't stop spinning but continues to swirl in apparent contradiction of the laws of classical mechanics). I'm not entirely sure of the reason helium would behave like that but I'm assuming its because its electrons are already occupying the lowest possible energy state in the atom while simultaneously filling that atoms highest energy "shell" (to invoke the Bohr model), which is the only thing I can think of that would make helium unique amongst the elements in a manner that would explain its boson behaviour.
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Sep 21, 2010 23:08
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Ms. Happiness posted:Where would you like to work after you finish graduate school? Cosmos Bios Theos is a great collection of Q&As on this topic from heavy hitters in the sciences. I'd say 99% come in as agnostic if not atheist. E: Question. Can you explain how quantum fluctuation works in the context of the universe springing out of nothingness? Even in a multiverse, didn't the first one have to start "being." Is this problem un-solvable? grendelspov fucked around with this message at 23:45 on Sep 21, 2010 |
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Sep 21, 2010 23:30
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Gavrilo Princip posted:Thanks! I've been looking for a simple-er explanation for Bose-Einstein condensates for a while. Doesn't the same thing happen with supercooled helium effectively behaving like bosons at ultra low temperatures? I vaguely remember something about it from a book or periodical or something, effectively quantum behaviour on a visible scale (for example, stir it and it doesn't stop spinning but continues to swirl in apparent contradiction of the laws of classical mechanics). I'm not entirely sure of the reason helium would behave like that but I'm assuming its because its electrons are already occupying the lowest possible energy state in the atom while simultaneously filling that atoms highest energy "shell" (to invoke the Bohr model), which is the only thing I can think of that would make helium unique amongst the elements in a manner that would explain its boson behaviour. Firstly, Helium-4 IS a boson, not just like a boson. Secondly, the phenomenon you are talking about, superfluidity, is only a sort of partial Bose-Einstein condensation. Unfortunately I don't know a whole lot about superfluidity. Helium-4, a boson, becomes superfluid at temperatures below 2.18 K, and helium-3, a fermion, becomes superfluid at about .0025 K. The difference is related to the fact that one's a boson and one's a fermion. The only reason that fermions can condense at all is because the fermions can pair up and form bosons. This is what happens in superconductors between the electrons and in fermionic condensates. For comparison, the first real Bose-Einstein condensate ever created in a lab was at a temperature of 170 nK, or .00000017 K. grendelspov posted:E: Question. Can you explain how quantum fluctuation works in the context of the universe springing out of nothingness? Even in a multiverse, didn't the first one have to start "being." Is this problem un-solvable? Even in quantum mechanics, something does not come from nothing (although it sure seems like it sometimes). The origin of our universe is either still a great mystery or a question that doesn't make any sense, depending on your point of view. It's pretty much a philosophical question. You can say, "where did our universe come from?" And if it has an answer, call it "A," then you might as well ask "where did A come from?" And so on. I don't think it's a solvable problem, or even a problem that makes sense. The universe just IS. Edit: This question reminds me of Godel's Incompleteness Theorem. Another good book recommendation is Godel, Escher, Bach: An Eternal Golden Braid by Douglas Hofstadter, a book about logic, music, Zen, self-reference, infinite regress, and the nature of human consciousness. It doesn't particularly fit in with this thread, which is about physics, but it's a good read nonetheless. DontMockMySmock fucked around with this message at 00:01 on Sep 22, 2010 |
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Sep 21, 2010 23:53
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I have attempted to explain on 2 different occasions why things float becuase of Archimedes principle. However, my g/f fails to understand this basic concept. Can you please explain to me how you would explain this.
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Sep 22, 2010 00:19
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sterster posted:I have attempted to explain on 2 different occasions why things float becuase of Archimedes principle. However, my g/f fails to understand this basic concept. Can you please explain to me how you would explain this. Show her this!  Click here for the full 970x1058 image. And if she doesn't understand "displaced" water, as I mention it in that graphic, grab two cups that nest into one another and demonstrate how the top cup pushing down into the water causes the water to be pushed up and out of the bottom cup. There's no substitute for doing the experiment yourself.
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Sep 22, 2010 01:06
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Have you heard of/what do you think of the "Theory of Elementary Waves"? It's a "theory" (quotes because I'm not sure I would really classify it as a scientific theory) that posits to replace/reform quantum physics. I'm pretty familiar with the basic concepts and ideas behind quantum physics and this seems more like two guys trying to make a name for themselves more than anything else. http://elwave.org/
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Sep 22, 2010 02:36
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Do superconductors actually have 0 electrical resistance? Or is it just small enough that it's pretty much negligible? Do you have trouble suspending disbelief in movies/TV? I'm an EE major and I can't stand when someone is being tortured with a 12V car battery. I took a modern atomic physics class a few years back, and I got it well enough - particularly the relativity stuff - but one things has always bothered me. If there are two objects moving at some high speeds (I think the numbers were .7 and .9c) away from a fixed point in opposite directions, how do you determine their speed relative to eachother? I took about 40 minutes on that problem alone on a test and got absolutely nowhere, before I finally put "1.6c, haha." I've tried reading about it in the book recently and I just can't figure it out. Help? Does taking a quantum measurement actually change the result? I have a good idea how Heisenberg's uncertainty principle works, but I was never totally clear about if it actually changes the result or if the result is just inherently inaccurate. And finally, what's the most work you've ever had to do to solve a problem? Physics major friends of mine who went on to take quantum mechanics after modern atomic said they had integrals which were the width of a sheet of paper. Is that pretty much standard for this type of work? Thanks ahead of time. suicidesteve fucked around with this message at 03:35 on Sep 22, 2010 |
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Sep 22, 2010 03:31
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Evan Montegarde posted:Have you heard of/what do you think of the "Theory of Elementary Waves"? It's a "theory" (quotes because I'm not sure I would really classify it as a scientific theory) that posits to replace/reform quantum physics. I'm pretty familiar with the basic concepts and ideas behind quantum physics and this seems more like two guys trying to make a name for themselves more than anything else. The first thing I read on the homepage of this website was a massive failure: "Quantum mechanics (QM) involves a lot of what is called “weirdness.” For example, do you think the moon only exists if people look at it?" ugh. Anyways, I watched some of his videos for physicists, and he hasn't fixed anything with quantum mechanics. It was proved a long time ago that quantum mechanics is cannot be both causal (effects following causes) and deterministic (no probabilities). I think that this guy has recovered determinism by throwing causality out the window. Not exactly a desired outcome, in most physicist's opinions! But mostly he's a crackpot. You get a lot of them in physics. At major general physics conferences they are always presenting on the last day, when most people are packing up and heading to the airport, and the not-crackpots who have spare time sit in and silently laugh at them. suicidesteve posted:Do superconductors actually have 0 electrical resistance? Or is it just small enough that it's pretty much negligible? Superconductivity is a type of Bose-Einstein condensation that results in exactly zero electrical resistance. It involves the electrons pairing up to create bosons called Cooper pairs. I can't really tell you much more than that, as I've never studied superconductors. I personally don't have any trouble suspending disbelief, most of the time. It's only when serious nonsensical  comes out that I have trouble. Like saying that suddenly solar neutrinos started interacting with the core of the earth, causing a reaction that will flood the earth several years later (this is the plot of 2012, a quite hilarious movie).Ah, velocity addition. So you start in frame of reference S0, and frame S1 moves to the right and frame S2 moves to the left. Write out the four-velocity of S2: (gamma2, -gamma2 v2, 0, 0). Now, do a Lorentz transform from S0 to S1: [(gamma1, -gamma1 v1, 0, 0), (-gamma1 v1, gamma1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1)] . (gamma2, -gamma2 v2, 0, 0) = (gamma1 gamma2 + gamma1 gamma2 v1 v2, -gamma1 gamma2 v1 - gamma1 gamma2 v2, 0, 0) (ugh, I hate writing out matrix multiplication in line). Then divide the 1-component by the 0-component to get the coordinate velocity: (v1 + v2) / (1 + v1 v2). Or, look it up. Quantum mechanics can be interpreted many ways. The most common interpretation is the Copenhagen interpretation, where when you make a measurement of a variable, it is randomly chosen from the set of possible answers according to the probability distribution function for that variable, then the system's state "collapses" to one which will always give that measurement (the corresponding eigenfunction). This point of view works, but it's only one of many points of view. Probably the homework assignments that took me the most time were for general relativity. Sometimes we'd spend hours on a single difficult problem. And yes, sometimes integrals can get pretty messy looking: a simple particle physics problem - high energy electron-electron scattering for example - can have over a dozen nested integrals (although most of them are trivial because the integrand will also have several Dirac delta functions in it). DontMockMySmock fucked around with this message at 07:23 on Sep 22, 2010 |
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Sep 22, 2010 04:46
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DontMockMySmock posted:turns heat into electricity (impossible) I haven't seen the movie... Are you sure you worded that right? I'm pretty sure most of our electricity comes from heat.
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Sep 22, 2010 05:11
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Sorry, you already answered this.
bit fucked around with this message at 05:54 on Sep 22, 2010 |
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Sep 22, 2010 05:29
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bit posted:This might be an odd question, but what are electrons made of? I know protons and neutrons are made of quarks and gluons (at least that's what I've been led to believe) but I've always wondered if electrons are actually quarks or quark-like particles themselves because they have so little mass compared to protons and neutrons. Sorry if this is a dumb question. He answered this.
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Sep 22, 2010 05:47
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How's the science in Primer?
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Sep 22, 2010 05:52
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What do you think you'd be studying if you hadn't gone into physics?
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Sep 22, 2010 05:52
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Can you explain Hawking radiation? I believe the idea is that particle-antiparticle pairs form, and the antiparticle goes into the black hole while the particle goes out. But why doesn't the opposite happen as well - an antiparticle being emitted and the black hole gaining mass?
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Sep 22, 2010 05:59
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tourgon posted:The following questions may be somewhat meaningless, but the concepts baffle me. Where this gets more interesting is that you can do the same thing with, say, the wavefunctions of an electron and derive the principle of least action in QM. (It was Feynmann who worked this out, if I recall correctly.) (Someone even did this calculation assuming a wormhole that could transmit things back in time and showed that causality violations just "don't happen" in such a system.)
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Sep 22, 2010 06:13
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DontMockMySmock posted:Ah, velocity addition. Stuff... I'll be honest, this is the only part of that answer that made sense to me (I haven't taken linear algebra or whatever class deals with matrices.) But it was still quite helpful. Thank you for that and for explaining superconductors in words I can actually understand, unlike Wikipedia.
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Sep 22, 2010 06:59
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squeakygeek posted:I haven't seen the movie... Are you sure you worded that right? I'm pretty sure most of our electricity comes from heat. What I meant to say is "heat directly into electricity." We get electricity out of heat as more heat moves from the hot place to a cold place. We can also dump energy into a hot place to move more heat from a cold place to a hot place (the opposite, refrigeration). What happens in The Core is that the "unobtanium" gives them electricity from the heat while also preventing heat from getting into the only cold place around (their vehicle) and frying them all. Cymbal Monkey posted:How's the science in Primer? Nonexistant. Apart from the one science fictional thing, which is the time machine, there's not really any science to it. The time machine itself behaves consistently and while its effects and operation is explained, the principle behind it is not, so there's nothing to judge. To any aspiring science fiction authors/screenwriters/etc. that may be out there: THIS IS HOW YOU DO GOOD SCIENCE FICTION. You don't need to do anything unreal except for the one thing that is the premise of your story, and you don't explain how it works because you don't know how it works because it's fictional. You just need to know what it does and explore the consequences of that in an interesting way. Desk Lamp posted:What do you think you'd be studying if you hadn't gone into physics? I have no idea. Math or theoretical computer science are probably most likely. Non Sequitur posted:Can you explain Hawking radiation? I believe the idea is that particle-antiparticle pairs form, and the antiparticle goes into the black hole while the particle goes out. But why doesn't the opposite happen as well - an antiparticle being emitted and the black hole gaining mass? Both scenarios happen, and the black hole loses mass in both. Antiparticles have mass-energy just like particles do, they don't have negative mass-energy. I say "mass-energy," referring to gravitational mass, to distinguish it from rest mass, which is a different concept. It can get confusing, sometimes; rest mass is an intrinsic property of each type of particle, and a particle's energy is a function of its rest mass and its momentum; energy is what causes gravity, and mass has energy, so I refer to it as mass-energy in this context. An antiparticle still has positive mass-energy and its escape will shrink the black hole. Keep in mind that Hawking radiation is an ad hoc theory that has never been confirmed (since we can't go around looking carefully at black holes). suicidesteve posted:I'll be honest, this is the only part of that answer that made sense to me (I haven't taken linear algebra or whatever class deals with matrices.) But it was still quite helpful. Thank you for that and for explaining superconductors in words I can actually understand, unlike Wikipedia. Fair enough, I assumed that you'd been introduced to the concept of the Lorentz transform, which is a rather simple matrix, but if you've never had linear algebra it requires more information. Basically, you know how you take one set of t,x,y,z and change it to the corresponding t,x,y,z in a different coordinate frame? You can also do that same transformation with other "four-vectors," and get the correct answer (i.e. replace the set t,x,y,z with the corresponding elements of the four-vector). Four-vectors have the cool property that the inner product of any two four-vectors is always invariant between frames of reference. The inner product is defined as a.b = -a0*b0 + a1*b1 + a2*b2 + a3*b3, and should remind you of the normal vector dot product (sometimes the zeroth term gets the plus and the others are minus, which doesn't matter so long as you are always consistent and are aware of the consequences). The most common four-vectors besides spacetime position are the four-velocity (dt/ds, dx/ds, dy/ds, dz/ds), the momentum-energy vector (E,px,py,pz), and the electromagnetic potential four-vector (phi,Ax,Ay,Az). I hope you've at least seen four-momentum before, in any class that teaches relativity?  Also I'd like to point out that I made a mistake in that post, I forgot the parentheses around the numerator. Goin' to fix it now.
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Sep 22, 2010 07:22
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DontMockMySmock posted:What I meant to say is "heat directly into electricity." We get electricity out of heat as more heat moves from the hot place to a cold place. We can also dump energy into a hot place to move more heat from a cold place to a hot place (the opposite, refrigeration). What happens in The Core is that the "unobtanium" gives them electricity from the heat while also preventing heat from getting into the only cold place around (their vehicle) and frying them all. Ah, so what you really mean is electricity directly from a high temperature. A transfer from one body to another is part of the definition of heat. 
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Sep 22, 2010 12:34
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How is it that Neutrinos changing flavour proves that they have mass? I kinda worked out that if they change flavour they must experience time meaning they travel at sub light speed meaning they aren't massless. Granted I've only taken AP physics (I too, love physics but I'm only in high school), so this is all from me working out why it would be the case) Also, why was Y4140 considered to have basically kicked particle physics in the shins? What about it clashed with standard particle physics so much?
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Sep 22, 2010 15:33
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Cymbal Monkey posted:How is it that Neutrinos changing flavour proves that they have mass? I kinda worked out that if they change flavour they must experience time meaning they travel at sub light speed meaning they aren't massless. Granted I've only taken AP physics (I too, love physics but I'm only in high school), so this is all from me working out why it would be the case) You're absolutely right about neutrino mass. Oscillation implies time for them to oscillate. Neutrinos are weird things, and the fact that oscillation was observed in relatively recent years has shaken up particle physics a lot. Before we talk about the Y(4140), we need to talk about Quantum Chromodynamics, the science of the strong nuclear force. And before we talk about QCD, we need to talk about quantum field theory in general a bit. In QFT, it's impossible to calculate anything directly or exactly. The only way we know how to do it is with perturbation theory - we find some small parameter (the coupling constant of the appropriate interaction/force), and we do a perturbative expansion (an infinite series of terms that become progressively smaller as the powers of the coupling constant go up). The more accurate we want to be, the more terms we must include in the perturbative expansion. A curious feature of QFT is that the coupling constants are not actually constant - depending on the energy of the reaction, they change. This is called the "running of the coupling," and is why you hear physicists talk about "unifying" different field theories (they are finding a theory where, at some higher energy, the couplings run together and the forces become indistinguishable - this has already been observed with "electroweak unification" of the electromagnetic and weak nuclear forces). Okay, so QCD. In QCD, everything's fine at high energies, but as the energy decreases, the coupling runs to greater than 1. This is bad news for our perturbative expansion! Terms of higher order in the coupling will now be bigger, and we're trying to sum an infinite series of ever-increasing numbers rather than ever-decreasing ones, which is futile. And yet, nature seems to have no trouble figuring it out - low energy solutions to QCD must exist, because there ARE bound states, like the proton and neutron. But we have pretty much no way of mathematically understanding why the proton and the neutron have the masses they have, nor the masses of any of the other hadrons we've ever observed (pions, kaons, etc.). So basically, we barely understand QCD at all. Fortunately there is a partial solution. A "model" that isn't a complete theory but manages to predict allowed decays, spins, charges, etc. without being predictive on the subject of anything where complicated math is involved. It's called the "quark model," and it was the brainchild of Murray Gell-Mann and Richard Feynman. Random trivia: Feynman kept referring to the particles as "partons," since they are the parts of hadrons, but Gell-Mann thought that this was an abominable marriage of Latin and Greek roots, so he chose what he considered a better name. "Quark" he got out of Finnegan's Wake, where there is the line, "Three quarks for Muster Mark" (there were three quarks in the original quark model), so if you've ever wanted to know how to pronounce "quark," it's supposed to rhyme with "Mark." But most physicists say "quork" instead. Anyways, the quark model these days has six quarks (and their antiquarks), called down, up, strange, charmed, However, you can also make structures of more than that many quarks. For example, an atomic nucleus is composed of many protons, and yet bound. But how does more than one colorless object stick together, if they have no charge? Well, they have no NET charge, but there are higher-order interactions because the nucleons have the color-charge equivalent of dipole/van der Waals interactions, which still manage to be very strong. "Well," you might be thinking, "if two baryons can be stuck together to make a deuterium nucleus, why can't you stick two mesons together or a meson and a baryon together?" Well, all mesons and baryons other than the proton are unstable, but let's not let that stop us. If two mesons are stuck together, you've got a structure made of four quarks (two and two anti-), so we call it a "tetraquark," and if you stick a meson to a baryon you've got a structure of five quarks (four and one anti-), so let's call it a "pentaquark." Now, because we can't calculate bound states in QCD, we have no idea whether such things can exist or what their masses would be like or anything like that. But people theorize about them anyway. The Y(4140), at first glance, seems to behave like a tetraquark ought. It may be the first ever discovered tetraquark, or it might be just a particularly unexpected meson, or it could be something stranger still. Hopefully, studying tetraquarks and pentaquarks, if they exist, will help give us insight into the incalculable realm of QCD bound states. So that's why everyone is so excited by it. Quite the trip, eh?
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Sep 22, 2010 19:03
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DontMockMySmock posted:Barbour's theories of timelessness don't seem to me like they could ever give you a testable prediction. Of course, maybe they can, and maybe they're right, and maybe someday there will be a cover of Nature that states in bold type "Time doesn't exist" under Greene's and Barbour's smiling faces. And then I'll look like an rear end. I know what you mean and having a testable, disprovable theory is a long way off (if indeed possible) but Barbour's work that formed the basis for that book was published in Nature. edit: I guess 'groundwork' might be a better word than 'basis' since there was a lot of work that was published after the Nature paper in other journals that are important to his pop-sci book as well. FightingMongoose fucked around with this message at 09:31 on Sep 23, 2010 |
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Sep 22, 2010 21:10
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DontMockMySmock posted:You don't have to think about it as a two-dimensional sheet expanding in three dimensions. Instead a better picture would be this: extend your piece of paper to infinity in all directions. Draw a grid of dots on it. Now, stretch it by a factor of two, so that the distance between each dot and its neighbor doubles. THAT is a good picture of what the expansion of the universe is like, and you never needed to think about the third dimension. It's also easy to extend to three dimensions without having to think four-dimensionally: just make it a 3D grid throughout all space, and expand that. That is what the expansion of space is like. The math to describe this is actually pretty simple once you know a little bit of relativity. That's pretty simple, but what is the actual mechanism driving the expansion? I'm asking because introducing the existence of dark matter and dark energy instead of assuming that that underlying mechanism of the metric expansion is wrong seems to violate Occam's razor. Of course if the rate of expansion directly follows from general relativity I can understand the eagerness to invent pretty outlandish alternative explations...
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Sep 22, 2010 21:33
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Your spin explanation, while interesting, has made little impact on my weak brain. But if you could briefly go back to it, it's the intrinsic angular momentum of a stationary particle? Also another question about orbitals. From what I understand electrons are not whizzing around in these things like comets flinging around our sun. But what are they doing? Appearing and reappearing in different parts of the orbital? Just popping in and out of different points, with the orbital just being a statistical distribution of where the electron is most likely to be? What would be a good math textbook for someone who has only gotten through two college semesters of calculus to start preparing them for understanding of physics on a mathematical level? Out of college an attempting to teach themselves that is. I understand I need to learn basics of linear algebra and diff eq, but what order should I try to tackle this stuff? I have my copy of Stewarts still but never got to multivariable calc, should I stick with that?
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Sep 22, 2010 21:38
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cyberbug posted:That's pretty simple, but what is the actual mechanism driving the expansion? I'm asking because introducing the existence of dark matter and dark energy instead of assuming that that underlying mechanism of the metric expansion is wrong seems to violate Occam's razor. Of course if the rate of expansion directly follows from general relativity I can understand the eagerness to invent pretty outlandish alternative explations... If the universe is expanding, it will continue to expand, unless something causes an opposite "force" to slow it down, such as the universe being full of matter (which naturally all wants to pull together). Originally, the universe was kept static in Einstein's theory by an ad hoc term called the "cosmological constant," which kept the universe balanced against all of the matter in it, so to speak. This was necessary because the universe LOOKED static at large scales. Then we realized that our galaxy isn't the entire universe, and pretty soon Einstein was calling the cosmological constant the biggest mistake of his career. Einstein was always one to let mathematical beauty drive his conception of reality, so he regretted adding the ugly cosmological constant instead of saying "these beautiful equations are telling me that the universe isn't static, so maybe it isn't." Anyways, almost as soon as we realized how big the universe was, we found out that it was expanding (a miracle, considering how inaccurate Hubble's data was that he used to jump to this fallacious but ultimately correct conclusion). Something called the "Friedmann-Robertson-Walker" spacetime was formulated to describe the expansion, which gave rise to the "Friedmann equation." Given that we know the universe is dynamic, the Friedmann equation tells you the dynamics. You can have spacetimes that expand, spacetimes that contract, spacetimes that expand then contract, spacetimes that contract then expand, or bounce back and forth. Furthermore, amongst these, you had ones which are flat, ones which are positively curved (like a ball), and ones which are negatively curved (like a saddle). When it comes to our universe, it was pretty clear that the universe was expanding, so the question became, "is there enough matter in the universe to reverse the expansion, or not?" This is related to the question, "is the universe flat or curved?", since that too depends on how much energy is in the universe. In a possibly-curved universe with nothing but "cold" (non-relativistic-speed) matter in it, if there is lots of matter, it will be positively curved and will cease expanding and contract. If there is exactly the right amount of matter, it will be flat and expand forever, but expanding ever more slowly as time goes on. If there is too little matter, it will be negatively curved and will expand forever at a rate that approaches some constant. Flash forward to today, and we know pretty much how much matter there is in the universe from looking at galaxies and gravitational lensing and such, and there's only about 30% of that special value that makes the universe flat, so you would expect the universe to be negatively curved. But the universe is also pretty much flat, as close as we can tell. So some other energy is filling the gap, making the universe flat. It's not radiation, there's barely any of that compared to the energy in the matter. It's something that we can't see, and so we called it "dark energy." Based on the dynamics of the universe that we have been able to observe, we've determined that dark energy is actually DRIVING the expansion of the universe, and it's accelerating. It's as if a "force," like the cosmological constant I talked about earlier, is pushing it. In fact, the cosmological constant has resurfaced as the most popular theory of what dark energy is. So to answer your question, dark energy is driving it. We don't really know what that is yet. Yiggy posted:Your spin explanation, while interesting, has made little impact on my weak brain. But if you could briefly go back to it, it's the intrinsic angular momentum of a stationary particle? Yes, spin is the intrinsic angular momentum of a particle, regardless of its motion. There's not really a whole lot more that can be said on the subject. Spin just is, just like charge and mass just are. In an atomic orbital, the electron is not "popping in and out" or anything like that. The orbital is a probability density function, a "statistical distribution" as you say, of the electron's position. It does not have a position until you measure it. This is what Einstein had so much trouble with, when he said "He [God] does not play dice." I mentioned it earlier, but I'll repeat it. There is no way to formulate quantum mechanics such that you have both "locality," the speed-of-light restriction that preserves causality, and "reality," there being real positions and momentum of a particle instead of them being probability distributions. It's not that the electron has a position and you just don't (can't) know it, it literally does not have a position. Weird, huh? For math stuff, I'd recommend Wolfram MathWorld to learn multivariable calculus. Just look up stuff when you need to, for that; multivariable calculus isn't hard. Linear Algebra is pretty easy to learn also, but it benefits from a more structured approach. Unfortunately I don't have a book recommendation offhand for a normal math course. However, a good quantum mechanics text (I suggest Griffiths' if you actually want the rigorous experience of it) will explain linear algebra all over, because you can't understand quantum until you understand linear algebra. Ordinary differential equations, as well as a couple key concepts in partial differential equations, are pretty essential to understand for a physicist, but if you're just studying it for fun you can just take the physics book's word for it that such-and-such equation has whatever solution. If you're willing to take a few classes at your local community college, you can take multivariable, linear algebra, and the first year's worth of physics and probably take a lot out of it. HOWEVER. Trying to understand anything beyond classical mechanics, classical thermodynamics, some basic electromagnetism stuff, and special relativity (the stuff they teach to first year physics students, all of which is accessible with basic algebra, trig, and calculus) mathematically is a serious undertaking, and I wouldn't suggest doing so unless you are going for a degree in it. It takes most people years of concentrated study to understand quantum mechanics. Electromagnetism is full of simple, easy-to-understand concepts that require mind-numbing amounts of calculus to actually apply. Quantum optics, quantum field theory, general relativity, and other fields require all that and more, to the extent that most physicists have never bothered to study them at all except for the one that they do research on. Most popular science depictions of physics are pretty bad, but the alternative is spending a very intense four years of your life learning what it all means and STILL not having all the answers. But if you love physics that much, it's all worth it.
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Sep 22, 2010 22:44
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Ok this is probably a really dumb question revealing my hangup, but then where is the electron, presuming we're not measuring it. Everywhere and nowhere within that statistical distribution, simultaneously? How does this stuff not drive you mad? I'm not disparaging, just a little baffled.
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Sep 22, 2010 22:59
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Yiggy posted:Ok this is probably a really dumb question revealing my hangup, but then where is the electron, presuming we're not measuring it. Everywhere and nowhere within that statistical distribution, simultaneously? The position of the electron isn't a "real" thing, in some sense, that's just the way it is. It drives a lot of people mad! That's why you get things like Einstein complaining about it and that "elementary wave theory" guy I was asked about earlier. But it's certainly easier to take when you know the math behind it.
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Sep 22, 2010 23:03
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Yiggy posted:Ok this is probably a really dumb question revealing my hangup, but then where is the electron, presuming we're not measuring it. It's not a dumb question. The problem is that you're assuming the electron is a thing with a fixed location even when we're not measuring it. Electrons aren't like small baseballs. I'm pretty sure quantum mechanics destroyed the classical idea of particles, to some extent. Edit: Beaten, and I forgot to post my question: Do you know of any good resources on physics for someone with a good math background but who has little physics background? Even when I looked at lecture notes which are supposedly physics for mathematicians they seem to expect knowledge of different notational conventions than I'm used to (but I can get over this) and intuition about physical systems (which I don't really have.) dirby fucked around with this message at 23:09 on Sep 22, 2010 |
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Sep 22, 2010 23:06
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