Quote:
Originally Posted by raymo
Again, as I understand it, there is no proof that photons are massless;
and if they are massless, maybe they would not interact with spacetime,
and ignore the curves and sail straight through them without deviating. Just
another thought to toss into the cauldron of complexity that is the
universe. I suppose the fact that photons travel at the speed that they do
comes close to proof of their mass,[assuming that relativity is correct, that is].
raymo
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If photons have mass then the scattering of a photon by another particle would follow the same physics as the scattering of particles in general, namely the energy and momentum changes of a scattered particle is a function of its velocity. Here energy and momentum are related to the particle's mass.
The situation with photons is very different. They do not undergo velocity changes after scattering. In this case the energy and momentum is related to the photon's wavelength. Energy and momentum changes occur due to a change in the scattered photon's wavelength.
Regards
Steven