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Is this proof of E=mc^2 ok?

  1. Nov 9, 2014 #1
  2. jcsd
  3. Nov 9, 2014 #2


    Staff: Mentor

    I don't know that I would call it a "proof", exactly, but the reasoning described in the post, which is based on a well-known thought experiment of Einstein's, is valid, at least as far as establishing that the energy of radiation confined in a box must contribute to the rest mass of the box in order for energy and momentum to be conserved. But that doesn't necessarily establish ##E = m c^2## as a universally valid equation.
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