Twin Paradox

In physics, the twin paradox refers to a thought experiment in Special Relativity, in which a person who makes a journey into space in a high-speed rocket will return home to find they have aged less than an identical twin who stayed on Earth. This result appears puzzling, hence the title of "paradox", but it is completely explained within the framework of relativity theory and has been verfied experimentally using precise measurements of clocks flown in airplanes.
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Since the Special Theory of Relativity predicted time dilation (slowing) with increasing speed relative to an observer - something amply confirmed in observation and experiment - an interesting effect might be experienced with twins. If one were to stay on earth when the other was rocketted to space, travelling at speeds approaching the velocity of light for some time, then return, one twin would supposedly have aged more. This does not happen, a fact accounted for in Einstein's General Theory of Relativity which deals with the acceleration and opposite effect of decelleration, upon the return flight.