I’ve been reading Brian Greene’s The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos. What a wonderful book! This is my third or fourth time through it and I find something new to appreciate each time.
In all likelihood, there are not only multiple universes, but an infinite number of them. This is what most versions of eternal inflation entail. The evidence for inflation grows stronger every year, and eternal inflation is the most likely variety of it.
Greene’s book explores half a dozen versions of the multiverse (multiple, or parallel, universes), and most of them are not mutually exclusive. There could be several flavors of parallelism at work simultaneously.
One likely aspect of the multiverse is what Greene calls the Swiss cheese model, in which our universe is like one of the bubbles in a block of Swiss cheese. The block has always existed, and has always been infinite in extent. (To those who ask, “Where did it come from?” I would reply, “Why should nothing be the default state? If there were nothing, we would be asking, ‘Who took everything away?’ …except we would not be here to ask that.”) The block expands due to processes that I only started to understand on this reading of the book and which I won’t attempt to explain here. In fact, it has always been expanding (but has always been infinite — infinity is a strange thing). Once in a while, a quantum fluctuation causes a “bubble” to form, one of which is our universe. These bubbles are carried away from each other in the expanding block, keeping them as isolated and distinct universes.
Because this has been happening forever, the number of bubble universes is already infinite. An infinite number are yet to come.
This post is not about how all that might work. For now, I only want to dwell on why I find this idea of infinite universes so comforting.
To appreciate it, you first must grasp just what infinity entails. Think of repeating an experiment an infinite number of times. If your experiment is to roll a pair of dice, then every possible outcome would happen at least once. In fact, it would happen an infinite number of times. Double-sixes? An infinite number of them. That’s amazing, but we’re just getting started.
Suppose your experiment is to thoroughly shuffle a deck of cards. Any outcome you can think of will be represented, including the outcome of the deck sorted just as it was when the box was opened: all the spades, followed by all the diamonds, clubs and hearts, and sorted by rank within suit. In fact, that will happen an infinite number of times. It’s harder to believe than getting an infinite number of double-sixes, but it’s true for exactly the same reason. Infinity is really big!
It’s so big that if instead of dice or cards, you were to play with a finite number of atoms arranged in a finite space, then every physically possible arrangement would be among the outcomes of the experiment. What is our universe, but a finite number of atoms in a finite space? Yes, if there are infinitely many universes, then others exactly identical to ours appear an infinite number of times (assuming, Greene hastens to add, that there’s nothing special about ours, and there is no reason to think there is).
Not only that, but there are others identical to ours except for that one detail of ours that bothers you the most.
That is the first comfort: If things have gone badly here, there’s a universe where they went well. An infinite number of them, in fact.
Of course, there’s also a place where they went much, much worse, so in case you’re a glass-half-empty sort of person let’s turn to the second comfort.
The nice thing about eternal inflation is that it will go on without us. Not only that, but when our universe has finally turned cold and dark, other universes will just be getting started, while in others the first life-forms will be starting to stir, just beginning their billion-year climb up the evolutionary ladder first to sentience, then to full awareness of their world, and finally to awestruck wonder at the universe they inhabit.
Why is this a comfort? Sometimes I feel responsible for so much. I have a family that is undergoing a lot of stress at the moment, a job in which I’m behind schedule, a book I’m writing, and even a musical instrument I have neglected for several months. I take my responsibilities seriously, but it’s nice to know that regardless of how well or poorly I do, the multiverse will go on without me.
It does not all depend on me or on you, even though sometimes it feels that way.
Look to the sky on the darkest, starriest night. Think about everything you see repeated in every possible variation, an infinite number of times. Think about the entire history of this universe, again repeated with infinite variations, more beautiful than the simultaneous play of a million kaleidoscopes. To think that all that beauty will continue to multiply with or without you … doesn’t that lighten the load?