Relativity implies that a moving clock experiences less passing time than a resting clock (relative to an observer). The "slowness"-factor gets higher the closer you get to light speed, reaching infinity (i.e. impossible) precisely at light speed.<p>In the example the one twin travels to a distant star with an appreciable fraction of light speed, thus ages slower. Then, the twin travels back, again with an appreciable fraction of light speed, and still ages slower.<p>This is basic relativity theory. Maybe I understand the article wrong, but from what I read I understood that the twin should somehow "catch up" on his travel back.<p>I'd love to be corrected.