Many folks might not realize it, but when we talk about “the multiverse,” we’re actually talking about a variety of hypotheses, particularly the many worlds, eternal inflation, and infinite repeating space interpretations. Each proposes a different way that we could live in a multiverse.
The many worlds interpretation is what people most commonly envision when thinking of the multiverse: a duplicate cosmos where everything is the same except you chose to wear red shoes today, or the Nazis won World War II — things like that. In other words: nifty “what if?” sci-fi daydreams. As The MIT Press Reader explains, the many worlds interpretation has roots in quantum mechanics, whereby unmeasured particle states do exist (up, down, clockwise, counterclockwise, etc.), but in their own universe.
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The eternal inflation interpretation was posited by physicist Alan Guth and has roots in the Big Bang. As Scientific American overviews, the Big Bang wasn’t an explosion in the way we think of it, but a rapid expansion — aka inflation — of space. But while inflation never stops, as Guth says, certain areas of space stop expanding and bubble into their own, pocketed universe. Hence, the multiverse is a collection of overlapping universes like frog eggs.
Finally, the infinite repeating space interpretation goes back to physicist Roger Penrose, who proposed that the universe continues to spawn subsequent universes, from one Big Bang to another, as Aeon describes. This notion, dubbed Cyclic Conformal Cosmology (CCC), creates a multiverse of sequential, ultimately infinite universes.
