Right, that’s the theologians ticked off. For my next trick: scientists.
Unlike theology, of course, we can’t dismiss scientific facts as untrue, no matter how inconvenient we might find them. But the implications of scientific discoveries get misinterpreted all the time.
Newtonian classical mechanics describes a mechanistic universe, one in which everything happens according to fairly simple, predictable, mathematical laws. If we know the exact state of everything at a given time, we can in principle know all future states, just by working out the maths. Such a universe is, in philosophical terms, determinist. But if people have free will, the argument went, it should be impossible even in theory to predict what they will do. If it’s possible to predict them, then they can’t be said to have any control over what they do, because it’s already determined before they decide to do it.
This was traditionally dealt with by means of substance dualism: the theory that the human mind was fundamentally separate from the body in such a way that preserved its freedom. This separate thing might be the soul, or the spirit — the important thing was that while it could affect, and be affected by the body, its internal processes were not bound by those effects. Descartes’ (in)famous I think therefore I am was part of an attempt to prove substance dualism.
Classical mechanics, of course, took a hell of a beating about a century ago, from relativity and quantum theory. Crucially, quantum theory is indeterminist. The most it can give us on the atomic scale, even in theory, is the probability of a thing happening. This is why we speak of the half-lives of radioactive materials, for instance: over any given interval, there’s a certain probability of a given atom decaying, and these probabilities add up over the billions of billions of atoms in a sample of plutonium to predict how much will be left after a certain amount of time. On a macroscopic level, then, the universe still appears deterministic, but fundamentally it isn’t.
Dualism has also, deservedly, fallen well out of favour, to the point where in some philosophical circles it’s more of a term of abuse, like creationism among biologists. If a theory entails or requires dualism, that’s all you need to dismiss it. There are a handful of (mostly theistic) philosophers who stick by it, but they’re a small minority; and, much more importantly, they’re simply wrong.
The indeterminism of quantum physics, however, doesn’t actually help us out of the apparent implications of determinism for free will. Firstly, the human brain mainly works on a macroscopic level; quantum effects are relevant to its electronics just as they are to artificial ones, but only to the extent that they are predictable. But even if the brain were entirely or mostly governed by quantum probabilities, it’s not at all clear how that would entail, or even allow for, free will in the usually understood sense of being free from determinism. We’d still be just as subject to the laws of chance as to those of physics.
Quantum effects and “free will” are supposed to be unpredictable, although in both cases they add up to predictable effects on large enough scales through the aggregation of probabilities. But the unpredictability of quantum effects isn’t caused by the free action of some unseen thing; it’s inherent in the fabric of reality. It’s no more indicative of intent than the result of a random dice roll, and there’s no reason to think it allows for free will as generally understood. Indeed, if it did, one of two things would be the case, neither of which we observe in reality.
The first would be that different probabilities would apply to quantum effects depending on whether they were inside a brain or not, or that quantum effects inside brains obeyed no predictable probabilities. That would be strong evidence for some sort of dualism, but no such thing has been observed — I don’t know if anyone’s tried, or how easy or obvious it might be; but it would be the story of the year in both physics and neurology if anyone had succeeded, and it’s not the sort of thing we can assume without checking. The alternative would be that everything in the universe has a conscious will. That would be interesting as a thought experiment (it shows up in Philip Pullman’s His Dark Materials fantasy series as a productive metaphor for a lot of ideas), but like the first option, it begs the question in the real world. We’d have to have independent evidence for pan-sentience, which, again, we don’t.
So physics doesn’t seem to allow for truly unpredictable free will. In fact, the fact that the actions of groups of people can often be more predictable the larger the group would seem to rule it out on its own. But this is a mistake. The essence of the problem, in one sentence, is that we’re looking for evidence of free will in the wrong place. We assume the evidence must take the form of irreducible unpredictability, that is, the sort that can’t be expressed even in terms of mathematical probabilities. There is an answer, but I’m trying to keep these posts to a manageable length, so I’m afraid it will have to wait for part three.
At least, that’s the deterministic explanation. The free-will explanation is that I like cliffhangers.