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Can light produce weak gravity waves?

  1. Sep 20, 2014 #1
    I have read online that light can produce a weak gravitational field (for example antiparallel beams should, in principle, attract weakly). This made me wonder if light can produce minute gravitational waves. Even if the waves were extremely weak (no disregarding of those high order terms in the applicable equation, whatever equation that may be), could the gravitational waves dissipate energy (on the order that is expected for cosmological redshifts) when light travels across cosmological distances ? I was thinking about the debunked tired-light hypothesis regarding the cosmological redshift, and I wondered if anyone has considered a mechanism whereby gravity waves dissipate energy.
  2. jcsd
  3. Sep 21, 2014 #2
    A graviton would travel at the speed of light too. So a photon could not emit a graviton ahead of it. Nor could it emit a graviton to right angles to the direction of a photon, for then it would be going faster than the speed of light, having a velocity c in the direction of the photon plus a velocity c to right angles. These two velocities would add to produce a speed faster than the speed of light and so can not exist. Also a photon could not emit a graviton in the direction opposite a photon. For then that graviton would be at rest, being emitted with -c from a photon traveling at +c. And a graviton cannot exist at rest. So I would have to think that a photon does not produce any gravitational effects.
  4. Sep 21, 2014 #3


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    The OP is correct that per GR, anti parallel beams attract. Further, a light beam attracts a particle of matter. Finally, the OP's guess that light can produce GW is correct. The following:

    "When electromagnetic waves collide, it appears that gravitational
    waves are always generated by the collision. These may be impulsive
    waves that occur along the boundaries of region IV only, or they may
    appear throughout the interaction region. However, they must always

    is a conclusion from


    However, there is no support for any 'tired light' concept, because an EM wave by itself, produces no GW.
  5. Sep 22, 2014 #4
    I'm not sure how that is consistent with photons passing through each other unaffected. If colliding photons produce gravitational waves, then it seems that the energy of the EM waves (photons) would be decreased by the energy of the gravitational waves that are emitted.
  6. Sep 22, 2014 #5


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    Well, this is classical GR. However, in QFT, photons CAN interact with each other via multi-loop interactions (the probability is just vanishingly small). For example, there is computable (exceedingly small) probability that colliding high energy photons can produce positron-electron pair without mediation of another charged particle. Thus, in a quantum gravity theory, it would seem expected that there is a chance of graviton production, and that the photon energy after interaction is reduced.
  7. Sep 22, 2014 #6
    Perhaps should you read: "One loop photon-graviton mixing in an em field; part2 arxiv:0710.5572v1, "As has been recognized many years ago... the quantized Einstein-Maxwell theory predicts the process of photon-graviton conversion in an em field..."
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