I don't know much about this, but just out of curiosity, how does Mathis answer that "dark night sky" problem (i.e., Olbers' paradox)? Essentially, if every photon ever generated was still in existence, being capable of merely be absorbed and then re-radiated, eventually they would all accumulate, and everything would be radiating brightly — even the thinnest of dust clouds. And yet when not being bathed in the light from our star (i.e., the Sun), we see mostly a dark night sky.

 

I'm of the opinion that photons, as EM waves, can be absorbed and re-radiated, wherein they are converted back-n-forth between Newtonian momentum of charged particles and EM waves. So the amount of energy in the Universe is constant, but how much of it is stored in momentum versus EM waves is variable. But I'm not even sure if that's a complete idea. ;)