Gravitational Waves vs Gravitons

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Discussion Overview

The discussion centers around the relationship between gravitational waves and gravitons, exploring whether gravitons are considered excitations of gravitational waves and the implications of gravitational wave observations on the existence of gravitons. The scope includes theoretical considerations in quantum gravity and string theory.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants question whether gravitons are postulated to be excitations of gravitational waves, suggesting that if gravitational waves are observed, it implies the existence of gravitons.
  • Others argue that there is no evidence supporting the quantization of gravity, indicating that gravitational waves, being solutions to classical equations, do not necessitate the existence of gravitons.
  • One participant notes that gravitational waves are derived from the linearized Einstein field equations, similar to how electromagnetic waves arise from Maxwell's equations, but this does not imply the existence of photons.
  • A participant raises a question about the necessity of gravitons in string theory, asking if they can be omitted if gravity is determined to be non-quantizable.
  • Another participant asserts that string theory predicts the existence of gravitons as part of its framework to unify quantum theory with general relativity.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between gravitational waves and gravitons, with no consensus reached on whether gravitons must exist based on the observation of gravitational waves or the implications of string theory.

Contextual Notes

There are unresolved assumptions regarding the quantization of gravity and the implications of classical versus quantum descriptions of gravitational phenomena. The discussion reflects varying interpretations of theoretical frameworks without definitive conclusions.

Islam Hassan
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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
 
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Islam Hassan said:
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.

Islam Hassan said:
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.
 
Islam Hassan said:
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.
 
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
 
Last edited:
String theory (to the best of my knowledge) predicts gravitons. The theory is supposed to unite quantum theory ith general relativity.
 

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