Speed of the graviton

[illinglsu]

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.

[ajb]

... 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.

[Kyrisch]

... 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.

[D H]

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.

[Moontanman]

Uh, i have a question, if gravity is indeed the bending of space time are gravitons even needed ?

[illinglsu]

well correct me if im wrong but i thought they still haven't proved the actual speed of gravity yet.

[Daecon]

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.

[brain-in-a-vat]

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

[ajb]

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.

[The Bear's Key]

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?

[proton]

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

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Kyrisch - I believe illinglsu is right. See http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html

Correctiob; He may be right.

[The Bear's Key]

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?

[theoriginal169]

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