Physicists describe the universe, or attempt to, using systems of equations. In order to create accurate descriptions, the equations make use of certain numerical constants — things like the speed of light and the strength of gravity.

What’s odd about these constants is that they seem almost have been fine-tuned so as to allow living beings such as ourselves to exist. If the force of gravity were just slightly smaller, for instance, stars and galaxies would never have formed. The entire universe would consist of a rapidly expanding cloud of gas. On the other hand, if gravity were just a little stronger, the stars and galaxies we see would all have collapsed into black holes. No planets, no sunlight, and perforce no scientists to look through telescopes and think about these things.

For those who believe in God, such a state of affairs is not difficult to explain. God created it that way, so that folks like us could come into being. Appeals to divine intervention are not, however, given much credence by scientists. Yet on the other side of the coin, it seems an awfully big coincidence that our universe should happen to have the characteristics that it is observed to have.

We do know that the universe we observe seems to have had a beginning, or something very like a beginning. About 13.8 billion years ago, our universe was extremely hot, extremely dense, and no bigger than the head of a pin. Since then, it has been expanding rapidly. Our most sophisticated observation and analysis suggests that it will continue to expand forever, and will indeed end (if that’s the right word) as a very thin, scattered cloud of cold gas.

Some cosmologists have proposed an explanation that would account for the seemingly custom-tailored nature of the universe we live in. It might be only one of an infinite number of universes, each of them with entirely random physical properties. Some of these universes would expand for a few minutes and then collapse again. Some of them would contain little or no matter. But if there are an infinite number of them, some would be rather like our own. In those, life as we know it could appear.

In fact, life could only appear in universes suitable for life, so all such universes would appear to be custom-tailored. What’s more, some universes (including, perhaps, our own) could be expected to have physics suitable for spawning new, baby universes. This process, of new universes budding off from older ones, may have been going on quite literally forever.

None of this is my own thinking, by the way. I’ve been reading The Book of Universes, by John D. Barrow.

It’s hard for the human mind to contemplate infinity. One of the odd consequences, if this multiverse of all universes has been going on forever, is that an infinite number of the other universes will look almost exactly like our own. So much like our own that you and I will be there — exactly as we are now, thinking exactly the same thoughts, or almost. Anything that can happen will have happened an infinite number of times. And in an infinite set of universes, anything can happen.

But wait — the concept is about to get a whole lot stranger.

In the past couple of decades, we have developed the ability to create sophisticated artificial models of complex systems, using computers. If we manage not to destroy all life on Earth, our ability to build complex models is bound to grow. In fact, if there is an infinite supply of universes, in some (a smaller but still infinite number) of which beings with complex intelligence can evolve, then it’s pretty much inevitable that some intelligent races will have developed the ability to create complex working models of entire living beings, entire planets full of life, or even entire universes.

The essence of such a complex model is that entities within the model would not know they were only virtual entities living within a model. Their experience — that is, the data that flows into them, and the behaviors they engage in as a result — would be of living in what to them is a real world.

This could be true of us. If we were actually virtual entities living in a simulated model world, we would have no way of knowing it. Welcome to the world of Philip K. Dick. What we think of as reality may be entirely constructed by vastly more intelligent beings. And their intentions might be benign, malevolent, or simply incomprehensible to us. In fact, given an infinite supply of universes, in some of them our creators’ intentions would be benign, while in others our creators would take delight in tormenting us.

What’s worse, they might have created our “real” world only last year, complete with “real” fossils, Roman ruins, galaxies that seem to be billions of years old, and everything else. Or they might have created only YOU. The rest of us might be amazingly realistic fakes — animations that disappear as soon as we’re out of your line of sight.

The word “might” in that paragraph is not adequate. If there are an infinite number of universes, some infinite number of which contain highly intelligent beings capable of constructing virtual models of intelligent beings, then in an infinite number of those universes you are an artificial construct who has been given the perhaps very temporary illusion that you’re real. In another infinite number of universes, however, you’re entirely real — made of real protons and neutrons exactly in the manner that you suppose.

And you have no way of knowing which of those two conditions you’re actually in.


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