Say you launch a rocket from earth, towards planet Zulu. The rocket travels at approximately c, relative to an observer on Zulu. Now, the rocket is pretty large, and fires a rocket from this rocket - a tiny rocket (so there's only a miniscule change in momentum). This rocket travels at a velocity almost c, towards Zulu - relative to the first rocket! Now, the observer at Zulu sees two rockets of almost equal magnitude of velocity heading towards it. But who arrives first? They both leave from the same spot at the same velocity relative to their target, but different velocity relative to each other. This is my problem: Who arrives first, and why? Edit: After thinking a bit about this, I realize that I'm probably going to get a couple of answers stating "massed objects can't reach the speed of light", it would take infinite energy. Well, that's fine with me, those who have a problem with that aspect can instead consider a situation where the first rocket travels at 0.4c, and the second one travels at 0.4c relative to the first rocket. According to my calculations, Zulu will see the second rocket travelling at 0.698c. The problem -for me- with this, is that for a given set of time, the distances travelled are different. If it takes 1 year for the first rocket to arrive at Zulu, the second rocket should use half that time, according to the first rocket, but Zulu will be expecting it somewhere between 1/2 year and 1 year. (can't be bothered to multiply). Where's the problem? Is there something about time dilation I should look into?