What is the relation between gravity and light?

  1. why did they have to be the same speed? do you think that this speed was somehow set as a standard speed for such things, i don't know maybe there are other things that are also in the speed of light.. so the speed of light isn't so rare..
  2. jcsd
  3. Chronos

    Chronos 10,348
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    GR sets a universal speed limit on 'communication' between objects in the universe. That limit happens to be the speed of light.
  4. Hipothetical particle responsible for carrying gravity is massless boson called graviton. Massless particles propagate at speed of light.

    If graviton is never confirmed to be real, then your question - why gravity propagates at speed of light - is very good question. Simply stating that GR forbids FTL communication, doesn't explain anything, because question is why speed of gravity propagation is exactly same as the speed of light propagation, not why gravity is not faster then light.
  5. Matterwave

    Matterwave 3,865
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    I think the "speed of gravity" can be worked out using GR...and it turns out to be c...but I've no idea how. :P
  6. Nabeshin

    Nabeshin 2,202
    Science Advisor

    Related thread:


    Edit: Also, on the grounds of dimensional analysis, we expect to get c. The only other really conceivable option would be for gravity to propagate instantaneously.
    Last edited: Feb 10, 2010
  7. Ich

    Ich 1,931
    Science Advisor

    A graviton simply inherits its properties from the classical wave it is meant to quantize. Whether or not there is a graviton is irrelevant, the speed is derived from linearized gravity, i.e. the wave solution in the weak field approximation.
  8. Chronos

    Chronos 10,348
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    Instantaneous speed of gravity has been thoroughly debunked AFAIK.

  9. could you please explain what you meant by "GR" and "FTL" ? :confused:
  10. mgb_phys

    mgb_phys 8,809
    Science Advisor
    Homework Helper

    GR = general relativity, Einstein's law of gravity
    FTL = faster than light
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