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 re: Some thoughts by e.g.)

i)Are you sure this requires General Relativity? I thought that that that was only required to describe gravitaional fields caused by matter?

ii)Either way both observers are accelerating relative to the other so why would one end up older than the other?

Posted by Sir Percivale on 2006-05-24 19:05:13