# Question #2363c

The photon has zero rest mass (${m}_{o}$), it travels at the speed of light in every reference frame.
But in terms of its relativistic energy ${E}^{2} = {p}^{2} {c}^{2} + {m}_{o}^{2} {c}^{4}$, then ${m}_{o} = 0 \implies E = p c$. So the photon has relativistic momentum and mass.