# Photons can have a constant rest-mass

The photoelectric effect proves that the light must be consisting of particles and on the other hand the wave nature of light was shown through the double-slit experiment of Thomas Young. In this experiment, we could observe the interference fringes that justify the light as a wave. But we know that the constant mass of the electron was proven and electron, the same as photon, have interference fringes in the double-slit experiment. Therefore, there is at least one example that a particle with constant rest mass has interference fringes in the double-slit experiment and the removal of constant rest mass, for photon, is not a good solution to answer the observance of interference fringes in the double-slit experiment. In this paper, by considering the constant rest-mass for a photon, we will express its various motions and present its energy equation.