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JulianM
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Mentor's note: this thread has been forked from https://www.physicsforums.com/threads/why-the-photon-has-no-mass.899792/#post-5912751
If the mass is zero then that formulation also yields zero energy (which we know is not true)
But momentum = mass x velocity so that part of the equation is E2 = c.(mv)lightarrow said:The correct equation, that is, the one which is always correct in special relativity, is:
E^2 = (mc^2)^2 + (cp)^2 (1)
p = momentum.
We know from classical electrodynamics that light's energy E is equal to cp. Then, from (1) you see that m must be zero.
lightarrow
If the mass is zero then that formulation also yields zero energy (which we know is not true)
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