From this link http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/headlights.html I don't understand the following..."Does time stop for a photon?. . . It is really not possible to make sense of such questions and any attempt to do so is bound to lead to paradoxes. There are no inertial reference frames in which the photon is at rest so it is hopeless to try to imagine what it would be like in one." In particular this statement "There are no inertial reference frames in which the photon is at rest". Can anyone explain that to me?