Einstein's Cosmos: How Albert Einstein's Vision Transformed Our Understanding of Space and Time (Great Discoveries Book 0)

by Michio Kaku

Einstein’s formula was not simply an academic exercise, because he believed that it might explain a curious fact discovered by Marie Curie, that just an ounce of radium emitted 4,000 calories of heat per hour indefinitely, seemingly violating the first law of thermodynamics (which states that the total amount of energy is always constant or conserved).

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.