Hey, I am 6 hours into a 12 hour audio course on Relativity. I love the course, but the bad thing is that you obviously can't ask questions. So here is a thought experiment I was hoping people could help me with. I am an observer standing between two rocket ships, R1 and R2. Each rocket starts flying at .75C in the opposite direction. R2 has a flash light on the rear of the ship shining back toward R1. 1. From the observer's frame of reference how quickly will the rockets be moving away from each other? 2. Will R1 ever see the light from the flash light shining back at it? If so, how quickly will R2 be moving from R1's perspective. Now let's take the same rocket ships and attach a string to the back of R2 that is wound on a spool which is attached to the back of R1. As the string is pulled off the spool, R1 should be able to calculate how quickly the ships are moving apart based on how quickly the spool turns. 1. What would R1 calculate the speed at which it is moving away from R2? Thanks a lot for your help!