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Relativity Video Check

  1. Aug 18, 2011 #1
    I made a relativity video for my father as he's been asking a long time.

    His question is basically how can light always travel at the same speed no matter where you are. So to answer it and since he's far away I made this video

    If someone could check it and let me know if it's wrong or any points are unclear before I send it to him. He worked as an engineer so the maths should be OK.
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Aug 18, 2011 #2


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    It seems accurate to me. But I don't think you've achieved an explanation of why every observer sees light travelling at the same speed. You've demonstrated via the transverse light clock that time dilation happens.

    One reason ( rather than an explanation ) is that Maxwell's equations tell us that the speed of light is a function of two universal constants ( scalars) which are naturally Lorentz invariant.
  4. Aug 18, 2011 #3


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    Nothing could illustrate better than this, the harm done by teaching SI units. The speed of light is not "a function of two universal constants". Look up 'Gaussian units' on Wikipedia, and read how ε0 and μ0 are not in any way fundamental, just an artifact of the SI unit system.
  5. Aug 18, 2011 #4


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    Thank you Bill.
  6. Aug 18, 2011 #5
    Thank you I've put your comment up on the video. When I finished it, I did start wondering how length contraction plays a role. I haven't really heard much about Gaussian units but I will give it a go.
  7. Aug 18, 2011 #6


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    Oh, that's a shock to me. So the idea that ε0 and μ0 are 'properties' is wrong ?

    Does this mean that Maxwell's equations give no support to the assertion that the speed of light is locally the same ?
    Last edited: Aug 18, 2011
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