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Light speed in relation to the size of the universe

  1. Jul 3, 2008 #1
    Can anyone tell me if the speed of light in a vacuum was the same a few seconds after the big bang when the universe was small as it is today? In other words could it be that the speed of light changes as the universe expands?

    Also is it actually known why light travels at the speed it does? If not then there is no point in me asking what is so special about that speed at which it travels with no varience.
  2. jcsd
  3. Jul 3, 2008 #2


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    There is no evidence that the speed of light has changed since the big bang.
  4. Jul 4, 2008 #3
    How can there be a doppler effect (red/blue shift) with light when the velocity of light doesn't vary relatively to the motions of source or observer???
  5. Jul 4, 2008 #4


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    It could, but as Mathman said, there's no evidence. Also, the speed can't vary in general relativity, so GR would have to be modified to allow for that.

  6. Jul 4, 2008 #5
    If we assume that light speed is variable over time then asa a consequence GR is no longer correct. GR requires that the local speed of light remains constant.
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