Difference between acceleration and gravitational field?

[curtdbz]

This is something I've always wondered... Einstein's equivalence principle says that you can't tell the difference between being accelerated in an elevator, or being in a gravitational field. No matter what, there's no mechanical device you can build, etc.

But, what about 'gravitons'? Aren't those supposed to be mediators for the gravity force (if they exist)? Can you tell by observing them that you're in a g-field and not an elevator that's accelerating?

 

[bcrowell]

I don't think the answer to your question is known, since we don't have a theory of quantum gravity. A theory of quantum gravity may have to throw out certain cherished principles of GR and QM, but we don't know which ones. If one of the principles to be abandoned is the equivalence principle, then the answer to your question would be yes. There are strong reasons to believe that gravitons can never be physically detected: http://arxiv.org/abs/gr-qc/0601043

 

[martinbn]

It is also possible that in an accelerated frame in empty space the graviton detector will detect gravitons. Some effect similar to Unruh effect.

 

[Mentz114]

It is also possible that in an accelerated frame in empty space the graviton detector will detect gravitons. Some effect similar to Unruh effect.

That sounds plausible. Maybe somebody can try accelerating the detector in bcrowell's reference to see if the cross-section increases

 

[bcrowell]

It is also possible that in an accelerated frame in empty space the graviton detector will detect gravitons. Some effect similar to Unruh effect.

This is sensible. There are pretty general arguments that the number of quanta is observer-dependent when you interface GR to quantum fields. (I think this is discussed in the appendix in Wald on quantum stuff, and also in Carroll.) The same would presumably apply when the quantum field is gravity itself.

 

[_PJ_]

That's an interesting point.
We'd have to detect and understand gravitons a little better, of course.

I personally believe, though, that the act of acceleration would require exchanges of gravitons in order to facilitate the exchanges of mass/energy.

 

[WannabeNewton]

Well the equivalence principle is also only valid for a given distance scale. If you look at a large enough distance scale you can observe geodesic deviation and can conclude that you are in a gravitational field and not simply accelerating.