Ok, so I just watched the nova fabric of the cosmos (blew my mind). Anyways, suppose I jumped on top of a beam of light and road it as it traveled out into space. Now, suppose that as I was traveling out there, another person is coming at me in the exact opposite direction on another beam of light. According to Einstein, if I was holding a radar gun, it would still say that the person on the other beam of light was only going 671 million mph (roughly), but what I don't understand is that if we are going opposite directions, why would my radar gun not change? I understand that if i flew by an observer on a beam of light, space would warp in order to not allow me to exceed the speed of light, but how would I perceive the person coming at me if we were both on a beam of light? Obviously it would only be an instant that we would see each other, but how would we perceive time relative to each other? If I looked at my watch and he looked at his, and I could somehow see the speed of his watch, which would be ticking faster and which would slow down? This is something that I have found fascinating, and I believe it is true, but it just blows my mind, and I'm really interested in it.