Hello, I was wondering how collisions would when both objects are travelling at c. Imagine 2 cars driving towards each other at a constant speed on a perpendicular course at regular speeds (not at c). Depending on how high their speeds are and their initial starting positions are they could miss each other or crash into each other in a variety of ways, ignoring the chance that they miss or that hit exactly on the right spot, there would be a certain chance for car A to hit car B's side, and the other way around. Whenever one of the cars (car B) travels at c instead, car A would always see B approaching at c no matter how fast it go itself. Because of this B could still easily crash into A's side, but as long as A isn't at c itself, then the chances would be almost impossible for A to crash into B's side. While B is moving at c, it seems it makes absolutely no difference what A's speed is to determine the chances of which cars side will be hit because A would always see B approaching at c. So if speed doesn't matter, what happens if they are both at c? Would they always miss, or hit each other on the sweet spot on the corner? Or do they just have a 50% chance to hit each other on the sides. Of course mass can't travel at c, so feel free to substitute cars for a line of photons moving towards another line of photons.