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clock paradox

n. (context relativity English) The phenomenon in which two observers who start together with identical clocks, follow different timelines, and then rejoin can have different elapsed times on their clocks, especially if one travels at a relativistic speed.

Wikipedia
Clock paradox
  1. redirect Twin paradox

Usage examples of "clock paradox".

So you can go a year, or a million years, or a billion-there seems to be no upper limit, and you will not be dilated-that's always an illusion, incidentally, there never was any so-called clock paradox, the clocks only seemed to differ when they were apart, much as a ship in the distance seems small though you know it is not.