illinglsu Posted May 11, 2009 Share Posted May 11, 2009 I was just wondering that if it turns out that gravity is mediated by the graviton, then wouldnt the graviton be the first true tachyon known. The reason why i say tachyon is through examples where gravity is obviously traveling faster than the speed of light such as in black holes. Just looking for some higher intellects to extrapolate on this. Link to comment Share on other sites More sharing options...
ajb Posted May 11, 2009 Share Posted May 11, 2009 ... examples where gravity is obviously traveling faster than the speed of light such as in black holes. I don't think this is correct. Sticking to classical gravity form the moment you can show that gravitational waves that travel at the speed of light. You can think of this as the speed that space-time reacts to small changes in the energy-momentum content. Gravitons are the quanta of these ripples. You can argue that gravitons are massless spin-2 fields. The massless part means that they travel at the speed of light. Link to comment Share on other sites More sharing options...
Kyrisch Posted May 11, 2009 Share Posted May 11, 2009 ... where gravity is obviously traveling faster than the speed of light such as in black holes. This isn't right. The reason light can't escape a black hole is not because the gravitons emitted are "traveling faster than light", but rather that the curvature of space within the event horizon of a black hole is so severe that the escape velocity (yep, just like that same velocity rockets need to exceed in order to launch into orbit) of the black hole exceeds the speed of light. Further, it is generally accepted that gravitons are massless and (therefore) move at the speed of light, although I don't know what experiments have been done to demonstrate this. Link to comment Share on other sites More sharing options...
D H Posted May 11, 2009 Share Posted May 11, 2009 This is the subject of several physics FAQ entries. Does Gravity Travel at the Speed of Light? How does the gravity get out of the black hole? Gravitational Radiation Some Frequently Asked Questions About Virtual Particles In particular, see questions 4 and 5. Link to comment Share on other sites More sharing options...
Moontanman Posted May 12, 2009 Share Posted May 12, 2009 Uh, i have a question, if gravity is indeed the bending of space time are gravitons even needed ? Link to comment Share on other sites More sharing options...
illinglsu Posted May 12, 2009 Author Share Posted May 12, 2009 well correct me if im wrong but i thought they still haven't proved the actual speed of gravity yet. Link to comment Share on other sites More sharing options...
Daecon Posted May 12, 2009 Share Posted May 12, 2009 I still think that there's no such thing as a graviton and it's actually space itself that's bending, instead of a force-carrier particle being responsible for gravity. At least, I'd like that to be the explanation. Link to comment Share on other sites More sharing options...
brain-in-a-vat Posted May 12, 2009 Share Posted May 12, 2009 (edited) Uh, i have a question, if gravity is indeed the bending of space time are gravitons even needed ?Particle physics and its Standard Particle Model predicts a graviton, while General Relativity is satisfied with curved spacetime. There are ongoing attempts to reconcile those two theories, but not too long ago it was thought that GR breaks down in the Planck regime, and that the discovery of gravity waves, i.e. the graviton, would solve the cause of gravity. Edited May 12, 2009 by brain-in-a-vat spelling Link to comment Share on other sites More sharing options...
ajb Posted May 12, 2009 Share Posted May 12, 2009 Uh, i have a question, if gravity is indeed the bending of space time are gravitons even needed ? I know I have discussed this before. A forum search should help. Anyway, gravitons are the quanta associated with fluctuations on the metric in the linearised Einstein field equations. There are inherently a perturbative notion, as are all particles. However, the existing methods of perturbative quantum field theory do not work when discussing gravitons. It is possible (and there is evidence) that general relativity (or something very close) is well defined in non-perturbative quantum field theory. (There maybe an non-Gaussian fixed point). So, it maybe possible that quantum gravity is not a theory of gravitons. Link to comment Share on other sites More sharing options...
The Bear's Key Posted May 14, 2009 Share Posted May 14, 2009 Here's a good one... Does it take the graviton longer to reach us (as would a photon) through expanding space? Hence, might it also become stretched -- much like a photon -- by this space expansion? Link to comment Share on other sites More sharing options...
proton Posted May 15, 2009 Share Posted May 15, 2009 I was just wondering that if it turns out that gravity is mediated by the graviton, then wouldnt the graviton be the first true tachyon known. The reason why i say tachyon is through examples where gravity is obviously traveling faster than the speed of light such as in black holes. Just looking for some higher intellects to extrapolate on this.Ant virtual particle can travel faster than the speed of light so they wouldn't be the first particles to be tachyon-like. However tachyons are real particles, not virtual particles. Kyrisch - I believe illinglsu is right. See http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html Merged post follows: Consecutive posts mergedKyrisch - I believe illinglsu is right. See http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.htmlCorrectiob; He may be right. Link to comment Share on other sites More sharing options...
The Bear's Key Posted January 26, 2010 Share Posted January 26, 2010 Here's a good one... Does it take the graviton longer to reach us (as would a photon) through expanding space? Hence, might it also become stretched -- much like a photon -- by this space expansion? Redshifted gravity anyone? Link to comment Share on other sites More sharing options...
theoriginal169 Posted January 26, 2010 Share Posted January 26, 2010 I know I have discussed this before. A forum search should help. Anyway, gravitons are the quanta associated with fluctuations on the metric in the linearised Einstein field equations. There are inherently a perturbative notion, as are all particles. However, the existing methods of perturbative quantum field theory do not work when discussing gravitons. It is possible (and there is evidence) that general relativity (or something very close) is well defined in non-perturbative quantum field theory. (There maybe an non-Gaussian fixed point). So, it maybe possible that quantum gravity is not a theory of gravitons. its possible i think cuz at motion your mass prevents you from c<speed but at gravity there is nomotion so noth prevents u Link to comment Share on other sites More sharing options...
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