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Comment Re:Two photons travelling in opposite directions (Score 2, Interesting) 415

You've just run into one of the classic problems of people just learning relativity. Specifically, you're assuming that the light has a rest frame. In the strictest sense, it doesn't, at least not a useful one. If you tried the basic equations, from which velocity transformations are derived, and assumed they held for photons, you would find that time does not pass for a photon. Obviously, this would be weird. You don't run into the problem until you get to something travelling at the speed of light, though, and you know the physics of what happens to that photon as long as you're in a normal rest frame, so the basic answer is that you simply don't try to go into the photon's rest frame, because that is meaningless. So, if two photons are going in opposite directions, you may see them going faster than the speed of light relative to each other, but that's never been what relativity was about. Relativistic velocities are only meaningful relative to your reference frame, and your reference frame can only ever be a safe non-speed-of-light one.

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