Is it possible to derive the speed of light from quantum electrodynamics (like it can be done from Maxwell's equations) or is the fact that the speed of light in vacuum is constant and has a certain value an assumption in the theory? My understanding is that QED assign a mass zero to photons and so, by assuming that special relativity describes space and time, photons must travel at the speed of light in vacuum. Based on this understanding don't we run into a circular contradiction? Special relativity was inspired by the constant speed of light that is predicted from Maxwell's equations. QED presupposes that special relativity is true but, at the same time, it replaces Maxwell's equations, therefore pulling the ground off special relativity.