The Twin Paradox

Penrose (2004: 420):

The most dramatic of these contains the essence of the so-called ‘clock paradox’ (or ‘twin paradox’) of special relativity. Some readers may be familiar with this ‘paradox’; it refers to a space traveller who takes a rocket ship to a distant planet, travelling at close to the speed of light, and then returns to find that time on the Earth had moved forward many centuries, while the traveller might be only a few years older. … the space traveller’s clock indeed registers a shorter total elapsed time than those on Earth.

Blogger Comments:

To be clear, this 'paradox' is an expression of the finding, predicted by the Theory of Special Relativity, that the ticking of a clock takes longer the faster the clock is moving; that is, that time intervals expand as the speed of a body increases. The longer the time intervals, the fewer time intervals (units) measured.