The Fabric of Reality was David Deutsch’s first book, written in 1997. Some discoveries, in particular the acceleration of universal expansion, have made certain parts of the book out of date, but it is still a fascinating read. It wasn’t as world-shattering as Beginning of Infinity, possibly simply because I read BoI first. But there was one section on free will that made me almost jump up and down (quite a trick, as I was on an airplane when I read it).
One of my biggest concerns with the multiverse view has been that literally everything that can happen must happen in some universe. The shorthand for this is that in some universe we are all psychopaths. But Deutsch made me see that this problem is actually the salvation of free will. How?
Consider the problem of free will in a classical universe. It can’t exist, because classically everything is predetermined. On some level everything is atoms and forces, and once you have the initial conditions of atoms and forces nothing can change. There’s no room for free will in such a universe. This is not only because the future must be determined precisely by the past, but also because there is no sense in which we have a choice about anything. All our choices are the result of atoms and forces, and no amount of special pleading about our consciousness can change the fact that we ourselves are atoms and forces. In a classical universe, what happens is what must happen.
Adding randomness, whether quantum randomness or some other kind, helps this situation not at all. We would never define our free will based on randomness, but rather on deliberate choices that we make. If all our choices are really just rolls of some non-classical (and therefore truly random) die, then free will is just as much an illusion as it was classically. Who cares if the result of the die roll is random? It’s still not in any sense a free choice we’re making. It’s just an unpredictable one.
But, as Deutsch points out, the multiverse is of a wholly different character. Consider a basic multiverse, with nothing in it that we might call alive. Indeed, in this universe, everything that can happen will happen. A splits into A and B, which then split into A, B, C, and D, and so on, a forever-branching tree with no differentiation whatever.
Now insert a living thing into this multiverse. Life is knowledge, and (as Deutsch said in BoI) “(K)nowledge is information which, when it is embodied in a suitable environment, tends to cause itself to remain so.” (BoI, p 123) What can this possibly mean in a multiverse? It means that we no longer have an evenly branching tree! Knowledge causes itself to remain embodied. Once you have knowledge, for instance a living thing, that living thing makes choices. How? Living things that aren’t people do it through variation and selection. Once you have plants in the multiverse, you’re going to have more than the expected number of universes in the multiverse in which plants survive and thrive. Variation and selection ensures that plants develop good survival strategies (because those are the ones that survive).
As a result, multiverses that otherwise would have gone their separate ways become more similar than they otherwise would have been. It’s not random that plants survive. It’s due to their choices, via variation and selection.
We know that people can create knowledge, too. Unlike plants and non-human animals, people create knowledge via conjecture and criticism. Our choices are much more like what we think of as choices, since they happen within an individual. We can let our theories die in our place.
So consider an individual human faced with a choice (whether or not to jump off a cliff, for instance). It is true that every possibility will happen in some universe, including that in some universe the human chooses to jump. But (and here is the point) in a much larger number of universes the human chooses not to jump. These universes, in which the human chooses to stay at the top of the cliff, will resemble each other more than could be expected. And it was the human’s choice, the human’s free will, that did it.
So now we see the true power of free will in the multiverse. By exercising free will, by making good choices, we make large sections of the multiverse resemble each other more than they would have. It’s almost so simple that you miss the beauty of it. With no embodied knowledge, the universes in the multiverse are non-descript playings out of possibilities, with the maximum possible spread between universes. With embodied knowledge, however, first in the form of living things and finally in the form of people, great swaths of the multiverse tend to look like each other. The knowledge-creators in those universes make the difference. By exercising their choices, they alter the very structure of the multiverse. Free will changes the world!