“By the end of this century, be able to ask whether or not we live in a multiverse, and how much variety its constituent “universes” display. The answer to this question 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).”
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What we’ve traditionally called “the universe”—the aftermath of “our” big bang—may be just one island, just one patch of space and time, in a perhaps infinite archipelago,” continues Martin Rees, Great Britain’s premier astrophysicist, in Nautil.us. There may have been many big bangs, not just one.
However, if the universe stretches far enough, everything could happen—somewhere far beyond our horizon there could even be a replica of Earth. This requires space to be VERY big—described by a number not merely with a million digits but with 10 to the power of 100 digits: a one followed by 100 zeroes. Ten to the power of 100 is called a googol, and a number with a googol of zeros is a googolplex.
The first Copernican revolution moved the Earth out of the center of the solar system. The second recognized that there are many planets in our galaxy, and the third that there are many galaxies in the observable universe. Proving that our universe is one among many would represent a fourth Copernican revolution.
Given enough space and time, all conceivable chains of events could be played out somewhere, though almost all of these would occur far out of range of any observations we could conceivably make. The combinatorial options could encompass replicas of ourselves, taking all possible choices. Whenever a choice has to be made, one of the replicas will take each option. You may feel that a choice you make is “determined.” But it may be a consolation that, somewhere far away (far beyond the horizon of our observations) you have an avatar who has made the opposite choice.
All this could be encompassed within the aftermath of “our” big bang, which could extend over a stupendous volume. But that’s not all. What we’ve traditionally called “the universe”—the aftermath of “our” big bang—may be just one island, just one patch of space and time, in a perhaps infinite archipelago. There may have been many big bangs, not just one. Each constituent of this “multiverse” could have cooled down differently, maybe ending up governed by different laws. Just as Earth is a very special planet among zillions of others, so—on a far grander scale—our big bang could have been a rather special one.
In this hugely expanded cosmic perspective, the laws of Einstein and the quantum could be mere parochial bylaws governing our cosmic patch. So, not only could space and time be intricately “grainy” on a submicroscopic scale, but also, at the other extreme—on scales far larger than astronomers can probe—it may have a structure as intricate as the fauna of a rich ecosystem. Our current concept of physical reality could be as constricted, in relation to the whole, as the perspective of the Earth available to a plankton whose “universe” is a spoonful of water.
Could this be true? A challenge for 21st-century physics is to answer two questions. First, are there many “big bangs” rather than just one? Second—and this is even more interesting—if there are many, are they all governed by the same physics?
If we’re in a multiverse, it would imply a fourth and grandest Copernican revolution; we’ve had the Copernican revolution itself, then the realization that there are billions of planetary systems in our galaxy; then that there are billions of galaxies in our observable universe. But now that’s not all. The entire panorama that astronomers can observe could be a tiny part of the aftermath of “our” big bang, which is itself just one bang among a perhaps infinite ensemble.
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