Einstein’s Test of Growing Old

None of Einstein’s ideas have so fascinated the public and provoked such controversy among physicists as the so-called “clock paradox.” This paradox is based on the assumption that time passes more slowly for an object in motion than one at rest. Thus, if Einstein is correct, an astronaut traveling at an extremely high speed, say to a distant star and back, would age less during his trip than a twin brother who had remained on earth. Depending on the length of his mission, the astronaut could, upon his return, actually be years younger than his twin. Man has not yet advanced far enough technologically to stage such a test of relativity. (Encyclopedia of Illustrations #13349).