I. The patchy universe
It has been some weeks since I realized what a dramatic assertion it is to claim that every event in the universe is determined in some fixed way by laws of nature and antecedent conditions. True, in the normal course of our experiments, we do not see causal determinism violated (setting aside for now quantum indeterminacy). But this is an unimaginably scant sliver of events making up the world. For every event we observe, there are countless ones we do not observe, or ones we do not observe with enough precision to tell us anything about the nature of their determination. And that’s just in the neighborhood of the events we measure. Out beyond Earth’s orbit, and in distant galaxies, and in the hearts of stars, and beyond black holes, are events too numerous for any analogy. We cannot even begin to say with any sort of confidence what is happening out there. And then there are the events in our past, to which there is no longer any access, and presumably all the ones in the future. So, in short, we observe quite nearly the smallest sampling we can possibly manage, a scarp of things here and now; and upon that evidence we make the claim that absolutely every event is causally determined? Ridiculous!
Don’t misunderstand me; I am not getting ready to argue for the possibility of free will or miracles. I am only pointing out, along with Hume I guess, that our confidence in causality far outstrips any evidence we have for it.
Now take up the quantum indeterminacy we had set aside. We have plenty of evidence for the claim that, in some circumstances, there is indeterminacy in the universe, meaning no fact to the matter of where a particle is, or how many there are, or what any of them is doing or how any of them are traveling. Indeed, the indeterminacy is not just a shortcoming in our theory; it is built into it, so that we are able to make the predictions we make only because we rely upon there being indeterminacy in the universe, an indeterminacy described by the formulas of quantum mechanics.
Put the earlier skepticism together with the confidence in quantum mechanics and what we have as a result is a very screwy universe. It is not at all as orderly as Messrs. Newton and Einstein would have had it. Imagine a pencil sketch of a mechanism, and now imagine a great many patches being erased away and not replaced by anything firm or definite. The only exceptions are the patches being measured or observed, or ones interacting fairly directly with those patches, in more-or-less determinate ways, with our eyes perhaps only half open.
II. Other worlds
It’s only been a comparative short while since I’ve begun to believe in other possible worlds. I’ve always regarded the idea as kind of kooky, but now it seems to me all too likely. It took us a while to discover new continents and cultures; and then other planets, suns, solar systems, galaxies, galactic clusters, etc. Following this progression makes it natural to infer there are other universes as well. And the inference is made more confident by the fact that many theorists are making more and more reference to these other universes, and using their goings-on to explain what’s going on in this universe. (Plus, I asked my poker pal Eastman Hatch about other possible worlds, and Eastman is an elderly gentleman who learned his physics from Feynman and is about as sensibly-minded as anyone I have ever met, and he says there probably are other worlds. So there. That is good enough for me.)
III. Weaving the worlds together
Now every time causal determinism fails (“open patches”), there is a range of ways to fill in the blanks. It may be that a given particle goes through one gate; or a second particle is created, and each goes through either of two gates; or a third is also created, which is almost immediately reabsorbed into the first, while the other two proceed through the gates; and so on. Again, QM gives us definite ways of describing these possibilities, along with their probability. Let’s suppose that all of these different ways describe the actualities in different worlds, so everything that could happen does happen in some world or other.
But in the situations I am describing, the open patch is over a stretch of spacetime, with fixed events around the borders. What I mean is that some portion of the universe is in state X at time 46, and in state Z at time 49, and the patch between the two is open: the patch could be filled with Y1/Y2/Y3 at times 47, 48, and 49; or Y112/Y113/Y114 at those times; or Y222/Y223/Y224, and so on. We have let all of these possible fill-ins for the patch come into being in different worlds, but all of these different worlds agree with the endpoints of state X at time 46 and state Z at time 49. Where these worlds overlap there is not a plurality of worlds; there is just the one world, with the way it is. Where they do not overlap, there are different worlds, of course.
So what we have, in the end, is our world cruising along, in some vaguely determinate order. Every so often a blank indeterminacy opens up, and our world splits into several different worlds, in which lots of different things happen. Then the patch closes up again, and we’re back to a single world once again. Maybe this happens a lot, or a little, or more here than there, or whatever. If QM is right, it happens almost everywhere almost all of the time.
IV. Making it personal
I don’t see why the open patches couldn’t crop up in our own personal spaces, where (say) my brain splits into several possible worlds, and perhaps I even have several different mental experiences, before the world sews itself up again into a single whole. I would not remember this happening, or at least I wouldn’t remember it in any way that privileged one of the possible brain sequences above any other. Maybe I would remember a vague sense of drifting along in thought, or chasing a cloud of different ideas at once. (This happens all the time, of course.) This would mean that, as I travel along through time, I am something of an army, marching in a file, then dispersing along different paths, before resuming a single path once more. Or to complicate the picture a bit further (since I do not believe the self is a unitary thing), maybe a part of me disperses along one cluster of paths, while another part disperses along another cluster, and the first part groups together again, followed by the second part, while a third now goes into disarray, and so on. And similarly, of course, with every other alleged “object” in the universe.
Well, maybe.
Huenemanniac 
I always thought you were a bit too dismissive of QM strangeness, because it only happens in the extremely small events that matter little to the big events of our larger world. I may have misunderstood you.
It is true that we seem to observed mostly large deterministic processes and the QM events are only on extremely small scales. Though I think it is better so say that quantum mechanics is happening in the all the vastness of the universe and within us. Each QM event with its indeterminate character is small, but the vastness of the events (everything) underlying all actions only become the deterministic classical physics we perceive in the enormous numbers of QM events underlying the large classical event. Our large world does seem to be cause-effect to our senses. We are not free to fly, alter our pasts, will a third arm, etc. There is growing evidence that our life choices are mostly based on our genetic machinery and our repetitive training by our environment.
The sliver of perceiving a will to choose might only be a mirage that I, like President Bush, am a decider. However, perhaps we have some sliver of will that is free and that is why we perceive it. We obviously have inflated the sliver, but perhaps when we feel the shame of the open questions of our terminal existenz then our brains have been developed enough to perceive and to will in the sliver of openness that the underlying sea of QM events permits.
Perhaps.
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