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DontMockMySmock posted:Can they? If you can prove they can, you've just earned yourself and Stephen Hawking a Nobel prize. Speaking of Hawking radiation, this article on Wired popped up on my RSS feed today. I haven't read it and just barely skimmed through it, but what I skimmed through I don't really understand anyway, but apparently some people think they have confirmed that Hawking radiation is real and if the paper is accepted by the scientific community then Hawking could win the Nobel Prize in Physics. Now, my question is, why would Hawking win it? It doesn't seem like he was involved with any of the experimenting. To me, it sounds like Hawking just theorized it but this other team is the one that spent time, money, effort, and man power to "prove" it, so this other team should be the one getting the Nobel Prize. Maybe I don't understand the significance of how much Hawking actually theorized, but in my mind it seems like the people who actually did the experimenting should be the ones who win the Prize. Do you physicists consider engineers to be a specialized subset of applied physics? --- This right here is my favorite equation:  The Second Law of Thermodynamics. This is the reason why your coffee gets colder and why your ice cream melts. Without it, we couldn't have invented air conditioners to cool your room in summer and heaters to heat up your room in winter. Without it, we would still be commuting with a horse-drawn carriage because the engine could have never been invented. Needless to say, we would have never conquered the skies (gliding doesn't count) nor gone to the moon, Mars, and beyond.
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Sep 29, 2010 22:12
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DontMockMySmock posted:You are technically correct, the best kind of correct. Because "infinity" isn't actually a number. But saying "there is no maximum temperature" and "the maximum temperature is infinity" are pretty much the same thing, except that one is more technically, mathematically correct than the other. Actually thinking about what I had said, wouldn't there "physically" be a temperature maximum, that being the instantaneous temperature at the start of the Big Bang? It would have dropped off quickly due to expansion obviously but energy is finite in a sense, right? Fun fact: RHIC currently holds the temperature record at 4 trillion Kelvin  , but it's only a matter of time for the LHC to overtake it once they start the PbPb beams.
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Sep 30, 2010 00:33
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Ziir posted:Speaking of Hawking radiation, this article on Wired popped up on my RSS feed today. As far as I can tell, this experiment does not confirm Hawking radiation, but instead confirms a similar analogue. They make a structure analogous to a black hole, except with distortions in the crystal replacing distortions in space-time. So then, what they think they are observing is like Hawking radiation except coming from the energy in the crystal distortions instead of the energy in space-time distortions. It's still pretty important, but it's not a confirmation of Hawking radiation like the popular science article claims. I didn't read the whole academic paper, though, so I could be misunderstanding it. Ziir posted:Now, my question is, why would Hawking win it? There have been times when two separate groups have shared a Nobel prize (although often made awkward by the fact that Nobel prizes can be shared by only three people). But it's also possible that Hawking would win on a different year than the experimenters. Hawking radiation is an important concept, and the theory is easily worth a Nobel prize, if it's correct. So obviously he can't win a Nobel prize until someone confirms the theory. Needless to say, the actual discovery of Hawking radiation would also be pretty Nobel-prize worthy. Ziir posted:This right here is my favorite equation: That's not even the purest, strongest form of the second postulate of thermodynamics. Here's the definition in my thermodynamics book by Callen: Callen posted:There exists a function (called the entropy S) of the extensive parameters of any composite system, defined for all equilibrium states and having the following property: The values assumed by the extensive parameters in the absence of an internal constraint are those that maximize the entropy over the manifold of constrained equilibrium states. *"Thermodynamics" is the biggest misnomer in physics, since in its purest form it only applies to static systems. But if you title a book "thermostatics and thermostatistics," people get confused. Ziir posted:Do you physicists consider engineers to be a specialized subset of applied physics? We consider them to be not scientists at all. 'Cause they're not. Except the kind that get PhD's and do research anyway, but then I'd rather call them "materials scientists" or "nanophotonicists" or whatever applicable term applies, rather than "engineers." Engineers are people who apply the things that science has found out in order to do useful stuff. They're certainly an important gearbox in the great machine of technological and cultural advancement, of which physicists and biologists and librarians and even English professors are also parts (well, some English professors anyway). EscalatorThief posted:Actually thinking about what I had said, wouldn't there "physically" be a temperature maximum, that being the instantaneous temperature at the start of the Big Bang? It would have dropped off quickly due to expansion obviously but energy is finite in a sense, right? Well, if the universe really was infinitesimally small at some point, then the temperature really was infinite also (in the limit). But then, current understanding of physics can't really go back all the way, so whodafuck knows?
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Sep 30, 2010 01:02
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DontMockMySmock posted:Well, if the universe really was infinitesimally small at some point, then the temperature really was infinite also (in the limit). But then, current understanding of physics can't really go back all the way, so whodafuck knows? Ah, of course. For some reason I had thought of a finitely small point as being the start.
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Sep 30, 2010 01:12
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Ziir posted:Speaking of Hawking radiation, this article on Wired popped up on my RSS feed today. I haven't read it and just barely skimmed through it, but what I skimmed through I don't really understand anyway, but apparently some people think they have confirmed that Hawking radiation is real and if the paper is accepted by the scientific community then Hawking could win the Nobel Prize in Physics. Right, this is a common result in solid state physics. The mathematics of something, like a black hole, or a magnetic monopole, are pretty well fleshed out considering they have no experimental evidence. When you consider the physics of a solid state system, you can find things that behave in an analogous way. With this "black hole", they key quality they want to emulate is the fact that light can enter, but not leave. There are various ways to trap light, such as metamaterials. In your paper, the black hole is created by a non-linear optical pulse. This means the index of refraction is changed slightly by the pulse. As a result there is a narrow range of wavelengths that will come to a stop relative to this pulse. What they then found was that photons were emitted sideways at the wavelength that was trapped behind the "black hole". The conclusion is that these photons come from the same theory that Hawking radiation is based on, so this demonstrates that Hawking radiation is possible if black holes behave the way we think they do. arXiv has both the experimental results and an 11 page derivation of why non-linear pulses are like black holes, but it's pretty dense reading. One odd thing is the Wired article says they sent a second pulse of light, but in the paper they specifically point out they don't put any light in at that wavelength.
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Sep 30, 2010 02:31
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With respect to all this talk about temperature, see negative temperature. Things with negative temperature are actually hotter than anything with positive temperature  It's a consequence of defining temperature more rigorously than [average translational energy] and more like [partial derivative of energy with respect to entropy].
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Sep 30, 2010 04:43
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Wow, I didn't realize you did theoretical astrophysics for a living. First off, thanks so much for your help in the physics thread. I basically want to what you're looking to do for a living: astrophysics. That was my reason for going back to school. I'm working through my B.S. at the moment. Where would you recommend I look for graduate studies in the US for theoretical astrophysics?
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Sep 30, 2010 04:49
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the posted:Wow, I didn't realize you did theoretical astrophysics for a living. The big ones are, of course, Caltech and MIT. Exactly what kind of astrophysics you want to do changes your options, beyond those two big ones. And, as far as I can tell from the questions you ask in the physics homework thread, you're still doing first year level classes, and as such you can't be sure you want to do astrophysics at all, much less what particular area of astrophysics, anyway. The top schools for physics in general in the USA, that come to mind, in no particular order, are Caltech, MIT, UC Berkeley, UC Irvine, Harvard, Princeton, Cornell, Ohio State, Stanford, and Chicago. That's a pretty short list and I'm sure I'm forgetting a few good ones. Outside of the USA all I can really think of is Cambridge, Oxford, and the Max Planck Institute. Now that I think about it, America sure does a good job of funding physics. That's why we built the atom bomb first, bitches 
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Sep 30, 2010 07:58
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Could you please answer a question? This is going to sound very stupid and I apologize for this in advance for I am not a very smart man, nor am I a physicist. So I heard all the matter in the cosmos is being dragged by the dick around the place by some unknown source of gravitation. And the scientists say that, poo poo, we think we are missing about a fuckton of matter from this here universe and this missing matter is to blame for all this bullshit. The scientists say that there is an invisible, undetectable matter all over the place and it is just there and you just deal with it. But to simple folk like myself this does sound like a very complex explanation for a very simple problem. My question is: why a simpler explanation to this problem cannot be accepted? Such as, for example, that there is a huge-rear end mass (or more) of matter outside of our visible universe and it is what is producing the gravitation that is making all this commotion? Sorry and thank you.
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Sep 30, 2010 13:53
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senier pomidor posted:Could you please answer a question? I'm also not a physicist but I think the idea is that there isn't enough conventional matter to provide enough gravity for the galaxy to stay together at the speed it is spinning, and it should expand outwards due to centripetal force. However, it isn't. This means there must be some additional source of gravity within the galaxy helping to hold it together. Might be totally wrong though.
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Sep 30, 2010 16:51
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Quick Scoop is right about the dark matter in our own galaxy. The orbits of matter in our galaxy deviate from what would be expected if ordinary matter was the only source of gravity. DontMockMySmock posted:But that's not the only reason we can tell there's dark matter. A different formulation of gravity might solve the galaxy rotation curve problem, but it has a hard time solving both that and the other deviations we see in and around distant galaxies. There are galaxies that seem to have a lot of light but little gravity, or a lot of gravity and little light. Dark matter explains this easily - the former is dark-matter-poor, the latter is dark-matter-rich (although there is a pretty strong correlation between dark matter and normal matter, there are deviations; there are also deviations with regards to how much light a given amount of normal matter gives off, but you can mostly correct for this by looking at the spectra and such). There is also evidence of dark matter in galaxy clusters, where we can see it through gravitational lensing. Compared to any other explanation that could explain all the things dark matter explains, dark matter is pretty simple. A big mass or masses outside the visible universe can't be responsible, because if it was outside the visible universe, it couldn't affect anything we can see in time for us to see it - gravity propagates at the speed of light also. Even if that was the case, there's no way it can explain the deviations in our own galaxy while simultaneously explaining the similar deviations in other galaxies and galaxy clusters.
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Sep 30, 2010 17:50
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Ok, that explains a lot for me. One thing is confusing, though: “gravity propagates at the speed of light” Gravity has a speed? When did this happen? I thought that speed is dependant on time (distance over time and all that) and time changes with gravity. So how can gravity has a speed if it can influence it?
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Sep 30, 2010 20:51
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senier pomidor posted:Ok, that explains a lot for me. Yes, gravity has a speed; it happened in 1915. And yes, gravity affects its own speed. Changes in space-time curvature (i.e. changes in gravity) propagate in the same manner as light propagates, and how they propagate is affected by the overall spacetime curvature. No information can ever go faster than that. here's a good explanation that involves dinosaurs, trips, and balls, three of my favorite things
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Sep 30, 2010 21:24
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DontMockMySmock posted:The big ones are, of course, Caltech and MIT. Exactly what kind of astrophysics you want to do changes your options, beyond those two big ones. And, as far as I can tell from the questions you ask in the physics homework thread, you're still doing first year level classes, and as such you can't be sure you want to do astrophysics at all, much less what particular area of astrophysics, anyway. The top schools for physics in general in the USA, that come to mind, in no particular order, are Caltech, MIT, UC Berkeley, UC Irvine, Harvard, Princeton, Cornell, Ohio State, Stanford, and Chicago. That's a pretty short list and I'm sure I'm forgetting a few good ones. Outside of the USA all I can really think of is Cambridge, Oxford, and the Max Planck Institute. You're right about where I'm starting, but this ain't my first rodeo  . I've already been through this university once when I got my B.A., so I will hopefully be getting through this program in less than three years. The reason I started back in for physics was for astrophysics, and there really isn't any other branch that "appeals" to me on a "Carl Sagan-esque" level. Could that change in the next few years? Sure. But not at the moment.
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Oct 1, 2010 00:44
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If light can't escape a black hole, how can gravity?
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Oct 1, 2010 03:50
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synapse posted:If light can't escape a black hole, how can gravity? 'Cause the gravity is already outside the black hole when the black hole forms. That's as much as I can really explain it without math. I'm not even sure that sentence made any sense, really, but it's as good a way to think about it as any. Black holes are pretty crazy! I find it's usually best to understand these sorts of problems through the math, but that obviously doesn't work here.
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Oct 1, 2010 03:56
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I've looked through this thread and haven't found this one yet: Could you write down the equations that define Einstein's General Relativity? I looked on Wikipedia and all sorts of places on the internet, but I've only found one sort of dinky little equation, but they say it's actually a whole bunch of equations, written in a very compact form. But people keep writing that it's something like ten equations. It's just something I'm really curious to see! EDIT: And another, more philosophical question -- Do you think that we have free will, or that the universe's fate is predetermined? DrSunshine fucked around with this message at 04:37 on Oct 1, 2010 |
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Oct 1, 2010 04:16
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When I watched Hubble 3D, the narrator mentioned that in a certain nebula that was photographed by the telescope, they found that winds in the nebula were blowing at over a trillion miles per hour. How were they able to measure this?
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Oct 1, 2010 04:43
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the posted:When I watched Hubble 3D, the narrator mentioned that in a certain nebula that was photographed by the telescope, they found that winds in the nebula were blowing at over a trillion miles per hour. How were they able to measure this? An easy to do astronomy lab is to take 2 pictures of the Crab Nebula, one from when it was first photographed and then one from recent times, and then, knowing the length (in light years) of the photos, you can compare how far the frontiers of gas have moved with a ruler. Then do simple math to figure out how fast it is expanding. I assume that something like this but more sophisticated was done with this other nebula. edit: You should then also be able to use the speed to prove that the winds have been traveling for about 1000 years and it must be the remnants of the supernova in 1054 Woke Mind Virus fucked around with this message at 04:59 on Oct 1, 2010 |
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Oct 1, 2010 04:54
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DrSunshine posted:I've looked through this thread and haven't found this one yet: Okay so this equation you have seen is actually only really half of GR. It's called "Einstein's equations of motion" and it goes something like this:  The G on the left with the subscripts is the Einstein tensor, a tensor that describes the gravitational fields, and the T is a tensor related to the stress-energy tensor, which describes the content of spacetime (and Λ is the cosmological constant and usually we assume it is zero or at least too small to matter, so ignore that for now). The other G (yeah it's kind of confusing) is Newton's universal gravitation constant, the same as in classical gravity, and c is the speed of light. So both G and T are symmetric tensors, which are basically the same as symmetric matrices, both 4x4 (since there are four dimensions of spacetime). A generic 4x4 tensor has 16 independent components, but since it's symmetric, there are six components above the diagonal that are the same as the six below the diagonal. So there are actually 10 independent components of each. The 16 components correspond to the four different values that each of mu and nu, the subscripts, can take (each 0, 1, 2, or 3, 0 representing a time-like dimension and 1,2,3 representing space-like dimensions). So for the 10 different independent components, there is a single equation, e.g.: G02 = 8 Pi G / c4 T02. So that is how this is really ten equations. Of course, they don't tell you anything unless you know how G and T are defined. I've already explained enough tensor calculus to confuse a lot of people, so I don't think I'll go into detail. Suffice to say that the curvature of space is determined by the matter, through these equations, and that each of these ten equations are second-order nonlinear differential equations that are all coupled to one another. It's a bit of a mathematical nightmare. But like I said, that's only half of GR. "Mass-energy tells space-time how to curve, and curved space-time tells mass-energy how to move." How mass-energy moves is determined by a set of conservation equations similar to those in classical mechanics, except that the divergence operator is replaced with something called a covariant derivative. These equations represent the conservation of energy, momentum, angular momentum, charge, particle number, whatever. The covariant derivative depends on the space-time curvature, such that the matter is induced to move. I won't put them here 'cause I'm too lazy to find a good version or upload a latex file of my own. They won't mean anything to you, anyway. They are first-order differential equations of the conserved variables' densities. You can also define how a particle will move with something called the geodesic equation, which also depends on the gravitational curvature, but in a slightly different way. tl;dr: the math is super-complicated, folks! I'm done typing about it, gently caress it. You can't really understand the math, nor comprehend how difficult it is to solve, unless you have a framework of multivariable calculus and differential equations, and are at least halfway through a course of tensor notation and basic GR. the posted:When I watched Hubble 3D, the narrator mentioned that in a certain nebula that was photographed by the telescope, they found that winds in the nebula were blowing at over a trillion miles per hour. How were they able to measure this? I would guess they were looking at the blueshift or redshift of gas traveling directly towards or away from us, using spectral lines. This is basically how all of this sort of thing is ever done. In a few cases of nearby nebulae and stars, as synapse mentioned, you can track the "proper motion" (motion in the plane of the sky, perpendicular to our line of sight) over long periods of time; see also: Barnard's star. I saved the best for last, folks: DrSunshine posted:EDIT: And another, more philosophical question -- Do you think that we have free will, or that the universe's fate is predetermined? No.
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Oct 1, 2010 05:31
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Please provide a simple answer to the question 'how do magnets work?' I need to know what causes one magnet to exert a force on another magnet.
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Oct 1, 2010 06:06
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When are we going to get some sweet pictures from Akatsuki?
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Oct 1, 2010 06:09
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Phlegmbot posted:Please provide a simple answer to the question 'how do magnets work?' I need to know what causes one magnet to exert a force on another magnet. Seconding this, but I've got a question of my own: How fast would I need to move in order to go back in time far enough to give Carl Sagan a big hug?
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Oct 1, 2010 07:22
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Phlegmbot posted:Please provide a simple answer to the question 'how do magnets work?' I need to know what causes one magnet to exert a force on another magnet. A mini tutorial. the posted:When are we going to get some sweet pictures from Akatsuki? I have no idea! But Venus isn't particularly sweet too look at, in my opinion - it just looks like some of the less interesting parts of Earth. It's not nearly so cool in comparison to nebulae and galaxies and globular clusters and other cool things. And then there's all the cool poo poo you can see without a telescope, just by walkin' around Earth with your eyes open. Venus is scientifically interesting, but I wouldn't call pictures of it "sweet." Nor mars or the moon, for that matter, once you get over the novelty of "ooooh it's another planet." They're basically the three least interesting things to look at that people are in the business of sending probes to. Tornado Lazers posted:Seconding this, but I've got a question of my own: Fast enough to come up with a new theory of physics where that's possible, and then prove yourself right. Does the ability to discover new physical law even depend on speed? I'd guess you'd want to go pretty slowly, because it's hard to solve equations while traveling past your desk at near the speed of light.
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Oct 1, 2010 09:15
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DontMockMySmock posted:A mini tutorial. I understand all of this, but it doesn't answer my question. Where does the force come from?
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Oct 1, 2010 12:36
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Phlegmbot posted:I understand all of this, but it doesn't answer my question. Where does the force come from? Here is a video explaining it from the greatest mind in recent times. http://www.youtube.com/watch?v=wMFPe-DwULM
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Oct 1, 2010 13:26
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Phlegmbot posted:I understand all of this, but it doesn't answer my question. Where does the force come from? Like Feynman said, this really can't be explained much more than "moving electric charges" to someone who isn't familiar with physics. As far as I understand, magnetism can come from either moving charges or from the intrinsic magnetism of particles which comes from another intrinsic property known as spin. What is spin? It's a type of angular momentum that all elementary particles possess as well as larger particles like nucleons and atoms. If you're asking how the force is transferred then it becomes even more difficult to explain. It arises from the exchange of virtual photons between magnetic dipoles IIRC.
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Oct 1, 2010 15:11
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Phlegmbot posted:I understand all of this, but it doesn't answer my question. Where does the force come from? The force from an ordinary permanent magnet comes from electrons, as is fairly well explained in the comic I linked. But if you ask "why," I don't really have an answer. Why do electrons do anything? They just do.
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Oct 1, 2010 18:01
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It's sort of like asking what gravity is (which I was thinking about last night). I can't really explain it without just using an equation. There's really no other way to do it. Gravity.... just is. It's one of the fundamental properties of the universe. If we were advanced enough to find out why gravity is, then I think we would be at the point where we could discover the true nature of our existence  .
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Oct 1, 2010 20:33
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Never has there been a more appropriate use of 2bong.
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Oct 1, 2010 20:54
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First off, let me thank you for taking the time to make this thread. You've done an exceptional job at explaining the subject in an accessible, yet thorough way. I have a few questions for you. My first one is academic in nature. I'm a 25 year old college drop out (of business school) and am strongly considering about - after taking a few night class in chemistry - going back to school full-time to study Physics. Would continuing to study at the graduate level be an option to me? I would probably be approaching 30 before completing a B.S., and I'm thinking that most people entering graduate school are 2-3 years younger than I am now. Also, what does the 8 signify in Einstein's equation of motion? I was looking at the derivations on Wikipedia, but the 4 pi G rho just kind of appear out of
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Oct 2, 2010 03:16
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oRenj9 posted:Also, what does the 8 signify in Einstein's equation of motion? I was looking at the derivations on Wikipedia, but the 4 pi G rho just kind of appear out of The 8 comes from a constant which is actually determined by deriving the classical Newtonian gravity from the Einstein Field Equations. Or so my wiki-ing tells me. A derivation of the constant is shown here e: I should stop trying to answer questions in a topic that isn't my own.
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Oct 2, 2010 03:20
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oRenj9 posted:My first one is academic in nature. I'm a 25 year old college drop out (of business school) and am strongly considering about - after taking a few night class in chemistry - going back to school full-time to study Physics. Would continuing to study at the graduate level be an option to me? I would probably be approaching 30 before completing a B.S., and I'm thinking that most people entering graduate school are 2-3 years younger than I am now. This is literally what I m doing right now, except I already have a B.A. I started back this semester to pursue a B.S. in Physics. I would wager, unless you're a genius, going straight to the graduate school would be impossible. Most schools wouldn't even accept an application if you didn't have a B.S. and numerous references. I'm turning 27 this year, and I'm hoping to be done with my B.S. in three years. I've already gone through this university once, so I have all the general education requirements fulfilled. And yes, you're right. All of the people in my classes are about 6-8 years younger than me. But who cares? I'm here, and I'm going to make it through. You should definitely go for it.
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Oct 2, 2010 05:40
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There's no reason to not pursue physics if that's what you really want to do. If you enjoy it, don't let age stop you. Just don't expect to retire quite as young as your peers. As for Einstein's equations' constant, well, EscalatorThief is right. The G in Newton's Law of Universal Gravitation is an constant of the universe that must be determined by experiment. If you write Einstein's equations as Gμν = k Tμν, then k is a constant of the universe that must be determined by experiment, and matching it with previously known data (such as through comparison to Newton's law and the known Newton's constant), it can be determined that k = 8 π G / c4.
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Oct 2, 2010 05:57
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Pseudo-scientific question forthcoming - apologies in advance if its ignorance is irritating. From what I understand, the faster something moves through space, the slower it moves through time, and that something's movement through space and time combined is always equal to c. If we thought about light emitted from our sun, for example, that departed from the sun 10 million years ago, would it be accurate to say that the light hasn't "aged" at all since then, since it's been traveling at the speed of light, therefore leaving itself no movement in the time dimension? If that's true so far, here's the thing I don't understand. I don't understand how light can have not aged at all when it's not like its travel is instantaneous. What I mean is, say the light was like "oh, here I go past the X galaxy," 5 million years later, "here I go past the Y galaxy." To the light it would not have been instantaneous, and it could say that it had reached X before Y, and therefore time had elapsed during the trip between the two galaxies, and if time had elapsed I dont see how it would be accurate to say light hasn't aged.
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Oct 2, 2010 21:56
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MyStereoHasMono posted:If that's true so far, here's the thing I don't understand. I don't understand how light can have not aged at all when it's not like its travel is instantaneous. What I mean is, say the light was like "oh, here I go past the X galaxy," 5 million years later, "here I go past the Y galaxy." To the light it would not have been instantaneous, and it could say that it had reached X before Y, and therefore time had elapsed during the trip between the two galaxies, and if time had elapsed I dont see how it would be accurate to say light hasn't aged. The light does indeed experience the trip as being instantaneous. That is, if you try to extrapolate from the equations used to describe massive objects at sublight speed, under the assumption that the same equations are also valid for describing a situation they weren't designed for and haven't been tested under. It's not at all clear that this is true, and you run into serious problems when you even try to define the question. For instance, I don't think anyone really knows what it would mean for light to "age." In our experience it never really seems to change of its own accord. And even when it interacts with something, particle physicists do their best work by assuming that the old photon has been destroyed and a new one has been emitted, rather than the old one "changing" in any way. And you can't accelerate a clock to lightspeed, so what does it mean to talk about time passing in that reference frame? Certainly it's hard to imagine even a clock, let alone a conscious observer, made out of pure light and other massless particles. It wouldn't do much but fly in various directions. We don't know how to describe the experiences of an object moving at the speed of light, and if I had to guess why, it's probably because such objects don't have experiences: at least not in any conventional sense. The same goes when you ask "If you move faster than light, do you go backwards in time?" which is something else that people have hypothesized based on the idea that a) FTL travel is actually possible, and b) the Lorentz transformations still give an accurate answer. It's fun to think about but there's not really any evidence for either of these. McNerd fucked around with this message at 00:26 on Oct 3, 2010 |
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Oct 3, 2010 00:17
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MyStereoHasMono posted:Pseudo-scientific question forthcoming - apologies in advance if its ignorance is irritating. It's important to remember that it moves slower through time compared to something else. Even if you leave earth at 0.999c, you still go through time perfectly normally according to yourself. However, it is true that something travelling at c can't evolve in time. This is why people figure neutrinos must have mass: they wouldn't be able to change through their different flavours if they were massless, and therefore moving at c. MyStereoHasMono posted:If that's true so far, here's the thing I don't understand. I don't understand how light can have not aged at all when it's not like its travel is instantaneous. What I mean is, say the light was like "oh, here I go past the X galaxy," 5 million years later, "here I go past the Y galaxy." To the light it would not have been instantaneous, and it could say that it had reached X before Y, and therefore time had elapsed during the trip between the two galaxies, and if time had elapsed I dont see how it would be accurate to say light hasn't aged. It's difficult to talk about what light would "see", because you're not allowed to actually change into the reference frame of something moving at c. However, if we look at the limit of something going at 0.9c, then 0.99c, and so on, we see the rest of the universe get closer together due to length contraction. The galaxy flattens into a plane, for example. You can imagine the light doesn't take any time to get from A to B, because to light, there's no distance between A and B.
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Oct 3, 2010 00:24
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MyStereoHasMono posted:Pseudo-scientific question forthcoming - apologies in advance if its ignorance is irritating. Wow, this makes more sense than any other way I have heard time dilation explained. I have a question: What is the relation between speed and time? What I mean is if you went 10% the speed of light around the Earth, would a trip take you 90% of the time it would seem to take from everyone on the Earth?
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Oct 3, 2010 01:14
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Quick Scoop posted:Wow, this makes more sense than any other way I have heard time dilation explained. I have a question: The difference in time is changed by the Lorentz factor. At 10% the speed of light it's about a 0.5% change.
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Oct 3, 2010 01:30
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Quick Scoop posted:Wow, this makes more sense than any other way I have heard time dilation explained. I have a question: The equation for calculating the effects of time dilation is actually really simple: t' = t*√(1-v^2/c^2) The effects really ramp up as you start pushing extra decimal places behind your percentage of C. Off the top of my head, I think travelling at 10% the speed of light would actually yield about a .5% difference in perception of time. ^^ Nevermind. Edit: Just so you know, the calculation for the question you asked looks like this: # of time units / the square root of (1 - (speed as a decimal of C^2/1^2)) To figure ten years traveled at 50% the speed of light: 10 / sqrt(1 - (.5^2/1^2)^2) The "1" inside the inner parentheses represents C. If you express your speed in terms of C, you don't really need it in there. Edit: Forgot to include some ^2s in the second equation. Centripetal Horse fucked around with this message at 22:16 on Oct 3, 2010 |
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Oct 3, 2010 01:30
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