This isn't hard proof, of course. But it's intriguing to remember that old saying, variously attributed to Picasso or sometimes the writer Susan Sontag, that if you can imagine something, it must exist.
And there might be something to that. After all, long before Hugh Everett sipped his sherry, numerous people in history imagined different versions of a multiverse.
Ancient Indian religious texts, for example, are filled with descriptions of multiple parallel universes [source: Sanskriti]. And in her book "Worlds Without End: The Many Lives of the Universe," Wesleyan University religion professor Mary-Jane Rubenstein notes that the ancient Greeks had the Atomist school of philosophy, which held that there were an infinite number of worlds scattered through a similarly infinite void.
In Medieval times, the idea of multiple universes also resonated. In 1277, for example, the Bishop of Paris even argued that Greek philosopher Aristotle had been wrong to say there was only one possible world, because that questioned an omnipotent God's power to create parallel ones. The idea was resurrected once again in the 1600s by Gottfried Wilhelm Leibniz, one of the leaders of the Scientific Revolution, who argued that there were many possible worlds, each with different physics [source: Wilkinson].