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Gravitational waves speed in a medium

  1. Feb 17, 2016 #1
    Electromagnetic waves are known to travel a c in a vacuum, but at lower speeds in a material medium.
    What about gravitational waves? They are also predicted to travel at c in a vacuum, but what about them traveling through material mediums? Do they get slowed down? by which factor?

  2. jcsd
  3. Feb 17, 2016 #2


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    I doubt there has been much work done on that. The calculations I have seen regarding gravitational waves have all assumed that outside the source region there is negligible mass-energy, and accordingly assumes the stress-energy tensor outside the source to be zero. Since a medium has mass, the question of speed through a medium would be outside the scope of such calculations.
  4. Feb 17, 2016 #3


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    See Ingraham, "Gravitational waves in matter," GRG 29 (1997) 117. Ingraham suggests that the best chance for seeing ##v<c## might be in "gravitational wave propagation through molecular gas clouds of galactic or intergalactic size." Although n−1 would be incredibly small, he suggests that you might be able to see an effect accumulated over thousands or millions of light-years.

    Note that the recent aLIGO result puts a very tight upper limit on dispersion.
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