Hi everyone, These days I've been reading about relativity (special) in a book of general physics, and I have a doubt about the reference system: If I stay on earth and I observe a rocket travelling away from the earth with a great velocity (let's be 0.5c), and I notice that time inside the rocket is slower than on earth, ok, that's allright, but, in the same way, the person who travels in the rocket will see that he's got velocity zero and the earth moves at 0.5c, thus a clock ticks slower on the earth. Which one of those people will get older faster? For each one will be himself, and no the other, whose seconds are loooong. Twin paradox confuses me... Thanks to all.