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 we’re 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? That’s 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. He’s not the guy you’d expect to stop and say it isn’t 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.