Hi, I am a little confused with this paradox. I asked my professor about it and he didnt really give a convincing answer. So the scenario basically seems to be some twins on earth(or anywhere) at rest, and then one leaves at relativistic speed for some time then comes back to see that his/her twin is much older than them. My question is, how come you can tell which one would age more? Why couldn't it just as well be the one on the ship? From the twin on earths reference frame, they are at rest and then the rocket flies away from them, while in the rocket frame it is at rest and the earth flies away from them. From each of the twins perspective the other one moves and they are stationary in their own frames. How come the same thing wouldn't happen to the twin on earth and find the rocket twin older when the earth arrived back at the rocket? I just took this paradox for granted for a long time but now I seem to be confused. Thanks for reading.