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Do Massless Particles Cause Gravitation?

  1. Mar 7, 2012 #1
    I know physical bodies with mass cause gravitation.
    But do massless particles, like photons, also cause gravitation ? I know they're affected by gravity, but would a cloud of photons bend space by itself?

    Thank you
     
  2. jcsd
  3. Mar 7, 2012 #2

    PeterDonis

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    Staff: Mentor

    Yes, photons have energy, and anything with energy causes gravitation.

    More precisely, photons have a non-zero stress-energy tensor, which is what acts as the "source" of gravitation. See, for example, this Wikipedia page:

    http://en.wikipedia.org/wiki/Stress–energy_tensor

    The stress-energy tensor of a source-free electromagnetic field, down the page, would apply to photons.

    I add this qualification because there are also cases where an "energy" can be assigned to the gravitational field itself, but this "energy" is not part of the stress-energy tensor and so it does not act as a "source" of gravitation in the above sense.
     
  4. Mar 7, 2012 #3

    jedishrfu

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    Staff: Mentor

    JA Wheeler once investigated the idea of a geon. Light traveling in a self perpetuating circle due to its own gravity.

    http://en.wikipedia.org/wiki/Geon_(physics)
     
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