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Why is the area normal to a beam of light rays invariant?

  1. Feb 10, 2015 #1
    It is a fact that all inertial observers would measure the same area normal to a beam of light rays in relativity. You can prove this by considering the displacement vector connecting a light ray to its neighbouring light rays. But I wondered if there were some intuitive explanation of why this must be true?
  2. jcsd
  3. Feb 10, 2015 #2


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    Gold Member

    Not really sure what you're looking for. Length dilation/time dilation?
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