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Varying spped of light

  1. Aug 2, 2004 #1
    I have to ask this question on this forum because i was shot down in flames when i bought the subject up in a physics discussion at uni.
    has the speed of light always been c?
    did it rapidly accelerate in line with the inflationary model of the universe or start instantaneously at c, and could it be possible that it is slowing down at the same rate the expanding universe is slowing down.
    I am going to throw the ball in the court of you clever ladies and gents because, I will confess, It may help me with a particular topic assighed to me by my tutor.
    many thanks
  2. jcsd
  3. Aug 2, 2004 #2


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    Staff: Mentor

    Its an interesting question and evidence is thin, but suggests it hasn't changed much (if at all). Remember, with telescopes we can see back in time and a different speed of light would cause very different looking galaxies, stars, etc.
  4. Aug 2, 2004 #3
    Thanks for your prompt reply Russ.
    This idea really came to me when i read the problem regarding the lack of mass/energy in the universe. now my idea( i wont call it a theory) goes on to sugest that if the speed of light had accelerated and is deaccelerating now then the size of the universe would be smaller than we have calculated. now this would help to solve partly the above mentioned problem.
    Now believe me i am not trying to flaw relativity but i am wondering whether, just as quantum mechanics and relativity are very good tools for predicting most of physics except singularities, they fail at the begin of time.
    do you think i should follow this line of thought or you my limited talents be better employed elsewhere.
    any guidance would be greatly appreciated
    many thanks again
  5. Aug 2, 2004 #4
    The speed of light is constant in space-time. It is reasonable to consider the possibility that as the universe increases through time that motion through space slows. While the speed of light in space-time is constant, as the theory goes, there is no requirement that the speed of light through space has been constant.
  6. Aug 2, 2004 #5


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    There is a lot of evidence to suggest that c has not varied significantly over time, at least not since a very long time ago. There would be a number of observational consquences, notably the nuclear fine structure constant, which have not been demonstrated. While a bit technical this paper gives a good overview

    http://horology.jpl.nasa.gov/papers/alpha95.pdf [Broken]

    For a dissenting opinion, try

    Last edited by a moderator: May 1, 2017
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