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When you read, you see that there are different opinions on the question, does a photon have mass?

From what I think, I know that a black hole's mass increases when it consumes photons, and everybody knows that a photon has energy and momentum. Since energy can be trasformed to mass, therefore a photon has mass.

The mass of photon is measured by dividing its energy by c

^{2}, that measured mass is the mass of a moving photon with its constant speed, the same speed in all reference frames.

If a moving photon has mass, then it must exert force on other particles. The exertion of force causes acceleration and therefore change in speed, and this violates the idea of constant light speed.

Can you correct me?

Thanks...