No, all I could find were qualitative discussions of the subject. But if you look at the relativistically correct equation for mass:Originally posted by marcus
Do you have a web reference to some sci.physics
conversation where a person who does not own
Lightman et al could read more about
the parallel case?
m2 = E2 - p2 (c = 1)
You can see that a system of anti-parallel beams has a net momentum of zero so m = E. On the other hand a system of parallel beams of light has a momentum of p = E and therefore m = 0.
This isn’t Lightman or GR but it’s pretty convincing.