Description: In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. The theory of relativity predicts that a person making a round trip will return younger than his or her identical twin who stayed at home. ///// When the traveling twin returns, he's younger and older than his brother who stayed put.