Quantum Mechanics Photons
The photon is normally assumed to have zero rest mass. If the photon had a small mass, this would alter the potential energy which the electron experiences in the electric field of the proton. Instead of V(r) = -(e^2)/(4(pi)(epsion_0)(r)) we would have V(r) = -((e^(2))(e^(-r/r_0)))/(4(pi)(epsilon_0)(r)) where r_0 is