Arguably the most famous thought experiment in relativity theory is the Twin Paradox. In this supposed paradox, one of two twins travels at near the speed of light to a distant star and returns to the earth. Einstein's Theory of Relativity dictates that when he comes back, he is younger than his identical twin brother, who stayed on the earth.
Explanations of this paradox have been poor and sometimes outright wrong. This topic is one of my hobbies, so I offered to write an article for Scientific American's Website to explain this phenomenon. My objective was to explain it so that a layman could understand it. Take a look at it and see if I was successful.