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

  • Thread starter aloshi
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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?
 

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tiny-tim
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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?
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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