This is a classic thought experiment relating to the Special Theory of Relativity.

Two twins of the same age start on planet Earth. Twin A stays on Earth while twin B travels far, far away and back at near the speed of light.

Because of Special Relativity, A looks at B's clock, and it moves slower than his own. So at the end of B's journey, A is much older than B.

However, B's frame of reference is equally valid. According to B, A's clock is moving slower than his own. So at the end of the journey, B is older than A.

What faulty reasoning leads to this apparent contradiction?

(In reply to Some thoughts by tomarken)

That's correct, and to take into account B's acceleration, you need the GENERAL theory of Relativity, not the "Special" one.

Posted by e.g. on 2006-05-24 17:41:12