Since photons are massless they can travel at the speed of light; but doesn't that mean that for them, relativistic time dilation is infinite, i.e., slowed to zero? They should be, in effect, immortal. This torpedoes the idea of red-shift changes being do to some kind of "light deterioration" that some people propose as an explanation of the acceleration of the expansion of the Universe. Photons could not deteriorate if time doesn't affect them.
Any other ideas out there on the effect of Time on Light?