By the end of this century, says astrophysicist Martin Rees, we should be able to ask whether or not we live in a multiverse, and how much variety of the laws of physics its constituent ‘universes’ display. The answer to this question, says Rees, “will determine how we should interpret the ‘biofriendly’ universe in which we live (sharing it with any aliens with whom we might one day make contact).”

The same fundamental laws of physics apply throughout the entire domain we can survey with telescopes. Were that not so—were atoms ‘anarchic’ in their behavior—we’d have made no progress in understanding the observable universe. But this observable domain, says Rees, may not be all of physical reality; some cosmologists speculate that ‘our’ big bang wasn’t the only one—that physical reality is grand enough to encompass an entire ‘multiverse’.

Even conservative astronomers, concludes Rees, “are confident that the volume of space-time within range of our telescopes—what astronomers have traditionally called ‘the universe’—is only a tiny fraction of the aftermath of the big bang. We’d expect far more galaxies located beyond the horizon, unobservable, each of which (along with any intelligences it hosts) will evolve rather like our own.”

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