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10 Jul 2012 15:17:39 IST

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what is a twin paradox???

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Janardhan K

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10 Jul 2012 19:13:57 IST

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In physics, the twin paradox is a thought experiment in special relativity, in which a twin makes a journey into space in a high-speed rocket and returns home to find she has aged less than her identical twin who stayed on Earth. This result appears puzzling because each twin sees the other twin as traveling, and so, according to a naive application of time dilation, each should paradoxically find the other to have aged more slowly. However, this scenario can be resolved within the standard framework of special relativity (because the twins are not equivalent; the space twin experienced additional, asymmetrical acceleration - when she switched directions to come back home), and therefore is not a paradox in the sense of a logical contradiction.

Janardhan K

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10 Jul 2012 19:19:21 IST

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u better see a video on youtube, it will be better for u to understand thru video......

Sagar Saxena

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31 Jul 2012 13:44:12 IST

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Special relativity tells us that a moving clock runs slow. So an astronaut who goes to a distant star at relativistic speeds and comes back will have aged less than his/her twin that stays home.

The apparent paradox lies in the naive application of the principal of relativity to the problem. If I think your clock runs slow because you are moving relative to me, you think my clock runs slow because I am moving relative to you. So you might argue that from the astronauts perspective, the twin at home should age slower.

This is incorrect, however. The paradox is resolved by the fact that the symmetry is broken when the astronaut turns around to come home. His reference frame changes. During that switch, the twin at home appears to him to age a bunch (by application of the Lorentz transformation--of course he doesn't just suddenly "see" the twin age). A good way of seeing exactly what happens is to imagine the twins sending radio messages to each other at fixed intervals. On the way there, the radio signals are redshifted--the interval is increased, so they come less often than they are sent. On the way home, they are blueshifted--the interval is decreased so they come more often. The travelling twin spends an equal time in redshift and blueshift mode. But the home twin sees a long period of redshift and then a shorter blueshift, so he sees fewer signals come from the astronaut, so he knows the astronaut aged less.

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