Originally posted by Pera
Yes, you were right about many things there, though the thing about photons left me wondering, I thought photons don't have mass at all? I mean, if photons can travel at the speed of light, they obvioysly can't have any mass. Or has the summer holiday made me forget everything about physics?
Photon's can exert their momentum onto another object (such is the principle of a solar sail), however they don't actually have to have mass to do that. In "classical" modern physics, photons have a zero rest mass, and since they have a rest mass of zero, plugging the value of 0 into the Lorentz equation to determine its mass at reletavistic speeds will give you an answer of 0. Otherwise, anything that has any mass will result in a mass of infinity upon reaching c.
Over the years there have been a few sensitive cosmological theories that would require photons to weigh something, even if it's only on the order of 0.000000000000000000000000000000000001g. Also, according to Einstein's General Theory of Relativity, gravitational fields can bend photons - while some may say that it's a matter of the interaction of the forces in some other manner, one of the fundamental principles of gravity is that gravitons interact with mass. At least, that's what I learned over the past 11 years. I've presented my own hypothesis on this in places such as the old VBB (and other places that seem to have died soon afterwards....), but I'll spare everyone this time around
