Most physics lovers asked themselves several times: Why should we limit the velocities in our nature to the velocity of light C ? And why a particle of light shouldn't have an ordinary mass even if the redshift or blueshift of light have been discovered.In my previous work about the michelson morley experiment, I concluded that the light can be studied easily like all the other waves. Actually, many scientists venerated the light by some theories that gave a limit to the velocities of photons and abolished their mass.This work makes a conclusion about Einstein’s relativity after an easy study about the Pound-Rebka experiment which deals with the Gravitational effect of light, and you will find also some logical remarks about the Doppler effect.