Question

Why the rest mass of photon is zero?? ​

Answer 1

Answer:

The nuclear strong force and weak force have very short ranges because of the mass of the exchange particles. The electromagnetic and gravity forces are precisely inverse square law forces with the implication of infinite range. This implies a zero mass exchange particle.

Answer 2

Answer:

               HERE IS YOUR ANSWER

Explanation:

The rest mass is the mass of a particle (in our case the photon) as measured by an observer who sees the particle still and with zero speed. ... But according to special relativity, light ALWAYS travels with the light speed c, and is NEVER at rest. And so it has zero REST mass.