multiverses

For some time, physicists have theorized about the existence of alternate universes. In fact, some models of physics require multiple universes, to explain some rarely observed phenomena. But, other than obvious ones like The Man In The High Castle Universe where the Nazis won WWII, the Earth-295 Age of Apocalypse Universe, and the Terran Empire "Mirror Mirror" Universe, just how many alternate universes are there? Well, some Stanford University physicists have answered that question, and the magic number is: 10^10^16 other realities.

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You're unique. Aren't you? One of the more creative hypotheses surrounding quantum mechanics posits the exact opposite. Though we can readily see only one world, quantum mechanics says that when were not observing the particles that make up that world, those particles exist in multiple places at once. There are many theories that attempt to grasp what this means, but one of the most tantalizing is Hugh Everett's multiverse concept.

Is all this work on string theory and multiple dimensions and extra universes still science? Thats the question physicist Sean Carroll and writer John Horgan recently debated. Carroll, of the California Institute of Technology, also blogs regularly for Cosmic Variance, and he wrote out a detailed post explaining his position. Obviously, as a cosmologist who works full-time on these seemingly preposterous ideas, he is a bit biased. Hes not the guy youd expect to stop and say it isnt real science. But his piece on the subject does effectively explain why he and, one assumes, other theoretical physicists working on these problems think this way.