In The Hidden Reality, Greene answers naysayers by turning their most damning evidence against string theory into an asset. The panoply of universes described by string theory, argues Greene, isn’t a failure of an overbroad mathematical framework. Instead, string theory is, in fact, tapping into a mind-blowing truth: that our cosmos is just one of a nearly uncountable panoply of cosmoses—that we inhabit a “multiverse” rather than a single universe.
If this seems like a drastic solution to the landscape problem, it is. This is not an elegant universe; it’s a byzantine mess with enormous philosophical implications. For example, the inhabitant of a multiverse is shadowed by countless doppelgängers identical to her in every possible way, as well as infinite others who are subtly and bizarrely different. For example, there would be a copy of you reading this review in Fookborum right now—and stumbling across this sentence would cause you to scratch your head in amazement with your prehensile tail. “You might argue that the bizarre nature of where we’ve gotten—infinite copies of you and everyone and everything—is evidence of the faulty nature of one or more of the assumptions that led us here,” Greene writes. Even though the consequences are indeed bizarre, he is rightly able to draw on the support of a large number of scientists who are now being driven to the same conclusion for reasons that have nothing to do with string theory. The most commonly accepted versions of the physical processes that took hold shortly after the big bang, for example, lead to the widely held belief that we live in oe of countless bubble universes that are floating in an infinite cosmic plenum. As Greene writes, multiverses are an almost inevitable conclusion of our current understanding of the laws of physics.
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.