I have read some of the stuff on this website but am still puzzled. I understand that E=mv^2 refers to the rest energy of the photon which presumably would be nil if the mass is nil. However, we never find photons in this state as they travel at the speed of light and at this speed they do have energy, presumably kinetic energy. We also know they have energy as they can be used in lasers. If this is kinetic energy, i.e. 1/2 mv^2, then again it is suggesting that the photon has mass, albeit a miniscule mass but mass never the less.So the question is, does the photon have mass or not? If not, where does the energy come from and what is the equation that relates energy to a mass-less state?