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Gravity as a particle-based force vs space-time warping

  1. Feb 17, 2015 #1
    I'm interested to understand the interpretation of gravity as a result of exchange of force particles (ie gravitons) vs General Relativity-based warping of space-time. Related to this is while a constraint to speed of cause and effect would apply to the graviton-based concept, why should this limit apply to space-time warping ? Re this latter point, I understand that while gravitational waves have been postulated there is yet no evidence of them (in fact recent 2014 findings appear now to have been caused by interstellar dust. So I think my question can be distilled down to how can the theories of gravity as a particle-based force vs a space-time warp be reconciled, and what are the key implications of this ?
  2. jcsd
  3. Feb 18, 2015 #2


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    In the same way it applies to all fields - there is nothing that transmits changes of the field faster than the speed of light.
    There is indirect evidence - not from BICEP2, but from observations of orbiting pulsars where they lose energy well in agreement with the predicted emission of gravitational waves.
    Gravitational waves appear in both approaches, in the same way as light can be described with classical electromagnetic fields or quantized (where the concept of photons appears).
  4. Feb 18, 2015 #3


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    Gravitational waves have not been postulated any more than EM waves were. Rather they were, like EM waves, predicted as the result of the theory. As the theory in question is both highly consistent and otherwise very successful, this gives them quite another level of plausibility than a mere postulate. I don't think many physicists were surprised when the pulsar result matched the predictions.
  5. Feb 18, 2015 #4


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    You should read this:


  6. Feb 18, 2015 #5
    My question why the limit would not apply to the gravitational (as opposed to eg electromagnetic) field theory (as opposed to graviton particle force theory) is due to the former being a movement of space-time itself, which is not limited by c. (This concept as I understand has been explored/utilised in the Alcubierre metric). So if one views graviity as a bending/movement of space-time itself why is the speed of impact of gravity constrained by c ?
  7. Feb 20, 2015 #6


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    But it would!
    Distance changes between distant objects are not limited by c, but all local processes are.
  8. Feb 25, 2015 #7

    Graviton is a quantum/fluctuation of the curvature of spacetime, a ripple ON TOP of the spacetime. However the background spacetime curvature itself results from a condensate or coherent state of a enormous number of gravitons, not few isolated ripples....this coherent state is so tightly correlated that individual graviton loses its identity and is part of something enormous, i.e. curved spacetime. I hope the distinction is clear. It is the difference between classicl EM field between plates of a parallel plate capacitor and isolated photons. Recall bosons have the tendency to gather together into a phase coherent lump in which the individual boson loses its identity and the lump as whole is a single macroscopic entity, called a condensate.
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