Cram Session: Parallel Universes in 200 Words

In this series, Life's Little Mysteries explains complex subjects in exactly 200 words.

Astrophysical data suggests space-time might be "flat," rather than curved, and thus that it goes on forever. If so, then the region we can see (which we call "the universe") is just one patch in an infinitely large "quilted multiverse." Meanwhile, the laws of quantum mechanics dictate that there are only a finite number of possible particle configurations within each cosmic patch (10^10^122 distinct possibilities, to be exact). So, with an infinite number of cosmic patches, the particle arrangements within them must repeat — infinitely many times over.  This means there are infinitely many "parallel universes": cosmic patches exactly the same as ours (containing someone exactly like you), as well as patches that differ by just one particle's position, patches that differ by two particles' positions, and so on down to patches that are totally different from ours. Furthermore, proponents of inflationary cosmology believe our quilted multiverse is just one of infinitely many bubbles that have inflated inside a larger multiverse. Because the fundamental constants can vary from bubble to bubble, each bubble can be wildly different; however, the possible values of the constants are finite, so the bubbles must eventually repeat. Thus, there are parallel universes within parallel quilted multiverses.

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