Gravitational Waves vs Gravitons

[Islam Hassan]

Are gravitons postulated to be excitations of gravitational waves? If so, and since gravitational waves have been unambiguously observed, then gravitons must exist, no?

If not, then what is the postulated relationship between gravitational waves and gravitons? Are both deemed/postulated to arise out of gravity quantum fields?IH

 

[Drakkith]

Are gravitons postulated to be excitations of gravitational waves?

Gravitons are hypothetical force carriers of the gravitational interaction. This includes gravitational waves and static fields.

If so, and since gravitational waves have been unambiguously observed, then gravitons must exist, no?

No. There's no evidence that gravitation is quantized like the other 3 fundamental forces are. It's entirely possible that gravitation isn't quantized and remains as described by General Relativity. Gravitons would only be required in the case that gravitation is quantized. As far as I know at least.

 

[Orodruin]

Are gravitons postulated to be excitations of gravitational waves? If so, and since gravitational waves have been unambiguously observed, then gravitons must exist, no?

No. Gravitational waves are solutions to the linearised version of the Einstein field equations. These are classical equations, just like Maxwell's equation for electromagnetism predict electromagnetic waves. You cannot predict photons from Maxwell's equations. What you can do is to check that QED reduces to Maxwell's equations in the appropriate limit, but the implication then goes in the other direction.

 

[Islam Hassan]

Slightly off-topic, but are gravitons necessary for the consistency of (one or more or all) string theories? Or can they be dispensed with within ST painlessly if and when gravitation is one day ascertained to be non-quantisable?IH

 

[mathman]

String theory (to the best of my knowledge) predicts gravitons. The theory is supposed to unite quantum theory ith general relativity.