What is Real?: The Unfinished Quest for the Meaning of Quantum Physics

by Adam Becker

String theory, meanwhile, doesn’t describe a single universe but instead describes a “string landscape,” a phenomenally huge number of possible universes—10500 or more. The similarities to the many-worlds interpretation’s multiverse were not lost on quantum cosmologists. The appearance of multiverses independent of Everett’s interpretation made its strange profusion of worlds downright appealing. Some physicists even proposed that all three of these multiverses—Everettian many-worlds, eternal inflation, and the string landscape—were in fact a single multiverse, and the three theories were simply describing the same reality in different ways. In any case, the many-worlds interpretation was (mostly) no longer laughed out of the room without serious consideration. Indeed, by the start of the twenty-first century, many-worlds had become the most popular rival to the Copenhagen interpretation itself among physicists, with particular popularity among cosmologists. But with wider consideration came the realization of a new problem, one that any theory with an infinite multiverse faced: the problem of probability.

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