Since the ancient Greeks first speculated that everything they observed in reality was the result of the interaction of tiny particles they called atoms, great thinkers have tried to find a single mathematical formula that governs and explains the workings of the entire universe. So far, though, even minds as brilliant as physicists Albert Einstein and Stephen Hawking have been unable to come up with that single grand equation of everything, also known as the theory of everything, or the final theory. Nevertheless, they continue to try, because without that final piece of the puzzle that is reality, the sum total of what we know falls a bit short of making sense.