The Twin Paradox


The Twin Paradox


The relativistic effects give rise to a famous so-called    paradox    of   two persons, say A and B, who are twins, born at the same time. Suppose that A flies away in a space ship at a speed comparable to the speed of light, leaving B stationary on the ground.


 B sees A moving fast, so that A’s clock appears to go slower from B’s point of view. If A comes back, he will find his twin brother B older than himself. The paradox arises from the contention that all motion is relative; so either twin could consider the other to be moving.

 Thus each should find the other younger, which is a logical contradiction. This contention presupposes that the twins situations are symmetrical and interchangeable. But this is not true. For the twins to meet and make the comparison, A has to turn around to come back. 

When the turns around, he feels the acceleration, while B feels nothing. Thus the situation is not symmetrical: there is a difference between the twins in the absolute sense. 


So the man (here A) who has felt the acceleration would be younger, and the paradox is resolved. 

In fact, it is one aspect of the theory of relativity which has been clearly demonstrated. Just as the mu-mesons live longer when they are moving, so will A live longer when he is travelling.   


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