This question already has an answer here:
I follow that time dilates / distance contracts as you move faster, but sees anomalies in what happens when you slow down again. The time changes are supposedly permanent, with an identical twin ageing a lot more than the twin brother in a rocket accelerating to relativistic speeds... The problem is: Suppose we send the one twin (call him the astronaut-brother) up in a rocket, circling the earth for a day, going close enough to light-speed so that supposedly fifty years pass for the ground-logged twin. Now the rocket slows down and lands. The astronaut brother supposedly finds his brother fifty years older than himself!
BUT we know during this process only one day passed for the observer (ground-logged brother). I don't see how the astronaut-brother can possibly find his twin, tens of years older in this scenario, once they're reconciled back in the same time frame?