" At rest, we know that its circumference is equal to p times the diameter. Once the merry-go-round is set into motion, however, the outer rim travels faster than the interior and hence, according to relativity, should shrink more than the interior, distorting the shape of the merry-go-round. This means that the circumference has shrunk and is now less than p times the diameter; that is, the surface is no longer flat. Space is curved. "