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Homework Help: How can we said that photon does not have a mass?

  1. Mar 3, 2010 #1
    how can we sad that photon does not have a mass? in my book they are a piece that there write at the photon influence of gravitation?
     
  2. jcsd
  3. Mar 3, 2010 #2

    tiny-tim

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    Hi aloshi! :smile:

    Mass is energy, energy is mass.

    A photon does not have rest-mass, but it does have mass.

    A box into which photons are inserted (from outside) weighs more, and exerts more gravity.
     
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