foodchain Posted July 7, 2007 Share Posted July 7, 2007 I don’t understand why this particle is put forward as is, does it not run counter to relativity at some level? Link to comment Share on other sites More sharing options...
ajb Posted July 8, 2007 Share Posted July 8, 2007 Once you understand what the graviton is then you will see that it is not in conflict with general relativity. We have recently discussed this. Search the forums Link to comment Share on other sites More sharing options...
foodchain Posted July 8, 2007 Author Share Posted July 8, 2007 Well, I read the thread and I have questions. Ok, gravity, its a product of mass curving spacetime. So then, is the graviton a particle that actually "conducts" or "mediates" this effect? Simply put if the graviton as by the standard model is a particle which causes gravity, then its not spacetime curvature from mass causing gravity? Or is the graviton supposed to be gravity for the subatomic realm? Link to comment Share on other sites More sharing options...
ajb Posted July 8, 2007 Share Posted July 8, 2007 You can think of the gravitational field as the metric on space-time. In that sense gravity is the local geometry of space-time. (I'd rather say local geometry than curvature because curvature has a specific meaning). The classical graviton is a linear perturbation of the space-time metric. The quantum graviton (the "particle") is the resulting particle upon quantisation of the classical graviton. I'll skip a load of technical issues here... It is in no way opposed or in conflict with general relativity. The graviton should be thought of as quantising general relativity. Link to comment Share on other sites More sharing options...
swansont Posted July 8, 2007 Share Posted July 8, 2007 To say that the graviton is or isn't in conflict with GR is a bit of a non-sequitur. GR is a classical theory, and the graviton is the proposed exchange particle for a quantum theory. Given our collective experience with classical vs quantum behavior in other parts of physics, it's expected that GR will fail at some scale. However the graviton behaves, it can't be inconsistent with GR wherever GR actually holds, much like the photon being the exchange particle for the EM interaction does not invalidate Maxwell's equations. It's the instances where the classical theory fails to work that the quantum nature becomes important/necessary. Link to comment Share on other sites More sharing options...
ajb Posted July 8, 2007 Share Posted July 8, 2007 Exactly swansont. They are not in "direct competition". Which I think was the question posed. And also, one has to explain what gravitons are. Maxwell's equations predict electromagnetic radiation just as Einstein's equations predict gravitational radiation. Quantise these and you get photons and gravitons. Link to comment Share on other sites More sharing options...
foodchain Posted July 8, 2007 Author Share Posted July 8, 2007 Exactly swansont. They are not in "direct competition". Which I think was the question posed. And also, one has to explain what gravitons are. Maxwell's equations predict electromagnetic radiation just as Einstein's equations predict gravitational radiation. Quantise these and you get photons and gravitons. So its not that the graviton is in conflict with GR, as much as its just the image of such on a quantum level? As I understand quanta currently, such does not denote solely particles, such as the electron for instance right? It also goes into discrete "packets" of energy such as the photon, but even that has the whole particle wave duality thing going on. My question then is such a relationship somewhat consequently to the reality of other particles, or quanta. I mean if light is not exactly a particle or a wave, could somewhat be said of gravity? I am trying to understand the graviton is all, and for it to have a infinite reach as I understand such mean that it escapes local geometry, or am I using that term wrong? I mean you have to get so close to a body, such as earth, before earths gravity attacks, on that note though, it would mean the local geometry or gravity, or what not is shaped perfectly to every possible point on the earth right? The other aspect then, would be the reaction to gravity and other forms of radiation, or electromagnetism I guess. Last question, I promise, at least for now. Going from what I understand, which is not a whole lot mind you, does this denote gravity, if as treated as a physical body here, has a velocity or speed, similar to the speed of light for instance? Link to comment Share on other sites More sharing options...
swansont Posted July 9, 2007 Share Posted July 9, 2007 I mean you have to get so close to a body, such as earth, before earths gravity attacks No. Gravity has an infinite range, as far as we know (which varies as 1/r2). That dictates that the graviton be massless. Link to comment Share on other sites More sharing options...
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