Wrong, James. I'm as open minded as anyone on this planet. It is you and some others who don't make the effort to think through the nature of the Unified Field Theory because you have already been indoctrinated with your Ultimate Creation Theory. Your religious view of the origin of the universe is easy to understand. What could possibly be easier than the whole universe starting from an instantaneous explosion? What could be more fundamentally religious than a light quanta that always was and always will be? Your view of a particle of light is that it goes on forever and does not experience decay, which is contrary to the law of equivalence. A photon is a unit of energy and so it has mass. If it didn't, it wouldn't exist. A photon is a unit of energy in a radiant state, which means that it exudes energy in the form of heat, which means it is attempting to disperse a portion of it's energy, which is a description of a particle in flux. For any particle to be in a radiant state, it's electromagnetic field must be extended further beyond the surface of the particle than when it is in a non-radiant state. At some point the light stream is going to reach a point in empty space where the leading photons are no longer constrained by the other photons all around them. The law of equivalence dictates that those leading photons will not be able to continue to be radiant and still maintain their total mass. The self preservation principle dictates that they will seek a rest state in which they are not dispensing their limited energy gratuitously. Therefore they will cease to radiate at a point that is most convenient for them to do so. Since they have dispersed some of their energy while in the illuminated state, they will then be a unit of energy of less mass.