I have questions: 1) twin 1 goes on a rocket flys to pluto at .99c and comes back to earth (all uniform motion, somehow). When he gets back he sees twin 2 is older. But since twin 2 was moving away from him at .99c why doesn't twin 2 see him as older? 2) Why does something gain mass as it approaches c? Appearently when you hit c you have infinite mass, and therefore need infinite energy to continue, so you cant hit c, but why do you even gain mass? i know you use the energy-mass equivalence to find out how much energy is turned to mass, but why cant it just get faster? I had more but i lost my train of thought, so more to come!