And once you become willing to take on the philosophical baggage of a multifoliate universe (and aren’t bothered by your countless identical twins), some of the deepest and most vexing problems about physics become easy to understand. All those nonsensical-seeming quantum-mechanical laws—that a particle can be in two places at once, that two objects can have a spooky connection that appears to transcend the laws governing space and time—instantly become explicable the moment you view our universe as one among many. And from Greene’s point of view, the 10⁵⁰⁰ different cosmoses described by string theory have ceased to be an unwanted artifact of the theory’s equations, instead becoming a factual description of universes that actually exist. Each of these universes is a bubble cosmos with its own cosmological constants, and as he says, “with some 10⁵⁰⁰ possibilities awaiting exploration, the consensus is that our universe has a home somewhere in the landscape.” Which is to say, string theory can no longer be accused of describing a landscape of fictional universes; our universe is just one in a collection of cosmoses as real as our own, even if we’re unable to see them. Multiversism is a radical, ambitious, and frustrating argument that relies on many lines of evidence and modes of thought—cosmological reasoning about the nature of the big bang, quantum-mechanical reasoning about the nature of matter on the smallest scale, information-theoretic reasoning about the nature of black holes—and it can be bewildering. Furthermore, Greene argues for nine distinct varieties of multiverse, each of which approaches the issue from a slightly different direction. And since the majority of his readers are untutored in the mathematical formalism that physicists use to understand the underpinnings of a scientific theory, Greene must use the much less precise tools of metaphor and simile to do the intellectual heavy lifting.

more from Charles Seife at Bookforum here.