Twin paradox
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In physics, the twin paradox is a thought experiment in special relativity involving twins, one of whom takes a space voyage at relativistic speeds and returns home to find that the twin who remained
During the ISS year-long mission, astronaut Scott Kelly (right) aged about 8.6 milliseconds less than his twin brother Mark (left), on Earth, due to relativistic effects.
Time dilation
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Time dilation is the difference in elapsed time as measured by two clocks, either because of a relative velocity, a consequence of special relativity, or a difference in gravitational potential betwee
Time dilation explains why two working clocks will report different times after different accelerations. For example, time goes slower at the ISS, lagging approximately 0.01 seconds for every 12 Earth months passed. For GPS satellites to work, they must adjust for similar bending of spacetime to coordinate properly with systems on Earth.
Marine sandglass MMM