Hume's Multiverse

Here's a nice little piece from IAI about reality not having any fundamental level to it. You might remember a previous discussion about this from another, more in-depth IAI piece which considered two main options : either reality becomes at some point self-referential, with some aspects being impossible to define without reference to others, or it's turtles all the way down.

Today's piece considers only the latter.

Perhaps reality has no foundation. Atoms, it turned out, could be divided into protons, neutrons and electrons, which it turned out could be further divided into quarks. Maybe we can keep going, further dividing and further dividing without ever reaching an end.

Why rule out the possibility of infinite regress in the composition of reality, whether that be infinitely many distinct layers, each more fundamental than the previous, or whether it be reality going in a circle, such that if you dig down far enough you discover the universe as a whole?

The claim that reality must have an ultimate level is often supported by little more than an appeal to intuition or incredulous bafflement at the alternative. If an argument is given, it is usually that reality must have foundations if anything else is to get off the ground. To go back to our analogy of the buildings, we might argue that there needs to be a foundational level for every other level to ultimately rest upon. If there is an infinite regress of distinct levels of reality, more and more fundamental but never ultimately fundamental, then (it is argued) there is nothing whose existence can account for the existence of everything else. A circular regression might seem even worse, from this perspective, since then every level of reality ultimately depends on itself, metaphysically bootstrapping itself into existence. The foundationalist, by contrast, can offer a picture whereby everything non-foundational ultimately inherits its existence from reality’s foundations.

Foundationalists take the ultimate beings - whether they be God, minds, quarks, quantum fields, or something else - for granted; there is no deeper explanation of where they come from. Why is an unexplained Prime Mover okay when an infinite regress of greater and greater movers is not, or a circle of things each moving each other? In fact, why isn’t it worse? The foundationalist posits some things that are, by definition, unaccounted for. In an infinitely descending or circular reality, at least everything is accounted for.

My objection would actually first be infinity : that once one invokes infinity, one is applying mathematical magic that can explain anything. This is why I concentrated last time on the idea of a circular, self-referential reality which would neatly avoid this. But yes, there's certainly also a nagging doubt about what something truly fundamental would mean. Supposing atoms were really indivisible, what would they be made of ? What is the "stuff" of a quark ? Why can't it be split ?

But perhaps I've let my own anti-infinity bias get in the way here, though I do still think any infinity means we've found a flaw in our mathematics. The issue for me is that infinity completely does away with causality, that one can simply point to an infinite multiverse and say, "our patch is the way it is because of sheer chance, all is probability, all parameter space must be occupied somewhere". This robs physics of any claim on meaning. Nothing is more or less real, it would seem, than anything else.

Or does it ? 

Recall that one about whether chairs exist. Let us suppose that the answer postulated, that it depends on the applicant conditions, is the correct one. In this way, perhaps infinite regress and causality alike can be cheerfully reconciled. If we can say that indeed, objects as we describe them do have some level of existence, then by the same token, we ought to be able to say that they experience certain processes. We can save causation thus. We might not have access to the true, fundamental nature of reality, but our observations of one thing leading to another are not meaningless either. Causality has the same level of reality as our observations do. If it's meaningful to say that a chair exists, then it is at least equally meaningful to say that pushing on a chair is what causes it to lean over.

Again, "equally meaningful" does not mean we've got at the true, underlying cause. We haven't considered electrostatic forces or atomic structure, let alone psychological motivations or the nature of mind. So Hume too, he can come along for the ride, happy that his seemingly bizarre claims that we don't understand causation can be saved after all. Rather the claim here is that our explanations for the cause of things are perfectly valid at the same level of the observations : they are correct, just not fundamental.

How does this hold up if there's nothing foundational but only infinite regress ? Well, at our level, the cause of the chair leaning is us pushing on it. At the atomic level, the cause of one atom moving is another pushing on it, with the existence of the experimenter being totally unknown and irrelevant. And at the subatomic level all is forces.

As we go down the levels, the ones above become less and less "real" in that they are less and less relevant. What seems to us to be truth, the existence of curious humans poking their noses into things because they want to, seem at first like at best emergent constructs : an atomic-scale observer wouldn't say a human is "real", just a collection of atoms that happen to be in a particular large-scale arrangement right now (just as some astronomers say exactly the same thing about filaments of galaxies). They'd say a human is no more than a label for that collection of atoms, not "real" in any fundamental sense.

And the deeper we go, the more detached from each other the layers become. At the subatomic the causes are electrostatic forces and the like. At even smaller scales it might be dominated by fluctuations in the quantum foam. Beyond that ? Impossible to say. We could likely not understand it anyway, even at the most - ahem - fundamental level. It would be utterly meaningless to us. To the denizens of this world, however, there might be yet smaller and smaller realms beyond. 

The point is that these levels do not affect one another. The processes at work simply do not exist in the different worlds, just as a single atom can't have a temperature but to anyone caught in a winter chill or a heatwave temperature becomes a very real consideration. So infinite regress does not mean avoiding causation : it means causation works on different scales, with there being literally zero chance of the smallest scales affecting the largest. This particular flavour of infinity isn't a mere substitution of meaningless statistics for physics.

Hmmm.