Does quantum mechanics rescue free will?

 

Philip Goff has challenged Kevin Mitchell’s interesting supposition that the indeterminacy of quantum physics creates some “causal slack” within which free will can operate. In essence, Kevin suggests (as I understand it) that quantum effects create a huge number of possible outcomes of any sufficiently complex scenario (like human decision-making), among which higher-level mechanisms of organismic agency can act to select one.

Philip responds that this won’t do the trick, because even though quantum mechanics can’t pronounce on which outcome will be observed for a quantum process with several possible outcomes, it does pronounce on the probabilities. He gives the example of his decision to water his dragon tree Susan (excellent name):

“Let’s say the Born rule determines that there’s a 90% chance my particles will be located in the way they would be if I watered Susan and a 10% chance they’ll be located in the way that corresponds to not watering Susan (obviously this is a ludicrously over-simplistic example, but it serves to make the point). Now imagine someone duplicated me a million times and waited to see what those million physical duplicates would decide to do. The physics tells us that approximately 900,000 of the duplicates will water Susan and approximately 100,000 of them will not. If we ran the experiment many times, each time creating a million more duplicates and waiting for them to decide, the physics tells us we would get roughly the same frequencies each time. But if what happens is totally up to each duplicate – in the radical incompatibilist sense – then there ought to be no such predictable frequency.”

It’s a good point, insofar as it needs an answer. But I think one exists: specifically, Philip’s scenario doesn’t really have any meaning. In this respect, it suffers from the same defect that applies to all attempts to reduce questions of human behaviour (such as those that invoke “free will”, a historically unfortunate term that deserves to have scare quotes imposed on it) to microphysics. The example Philip chooses is not “ludicrously over-simplistic” but in fact ill-defined and indeterminate. I don’t believe we could ever determine what is the configuration of Philip’s particles that predisposes him to water Susan. It’s not a question of this being just very, very difficult to ascertain; rather, I don’t see how such a configuration can be defined at the quantum level. We would presumably need to exclude all configurations that lead to other outcomes entirely – but how? What are the quantum variables that correspond to <watering Susan> or <not watering Susan (but otherwise doing everything else the same, so not cutting Susan in half either)>? What counts as “watering Susan”? Does a little water count? Is watering Susan before lunch the same as watering Susan after? This is not a simple binary issue that can be assigned Born probabilities – and neither can I see how any other human decision-making process is. (“Oh come on: what about ‘Either I press a button or I don’t’”? But no, that's not the issue as far as free will is concerned – it’s ‘Either I decide of my own volition to press the button, and I do it, and the botton works’ or not. And what then is the quantum criterion for ‘of my own volition’? How do we know it was that? What if I was bribed to do it?... and so on.)

Obviously such scenarios could go on ad infinitum, and the reason is that quantum mechanics is the wrong level of theoretical description for a problem like this. We simply don’t know what the right variables are: where the joints should be carved in an astronomically complex wavefunction for many particles that correspond to the macroscopic descriptions. And again, I don’t think this is (as physicists often insist) just a problem of lack of computational power; it’s simply a question of trying to apply a scientific theory in a regime where it isn’t appropriate. The proper descriptors of whether Philip waters Susan are macroscopic ones, and likewise the determinants of whether he does so. At the quantum scale they don’t just get intractably hard to discern, but in fact vanish, because one is no longer speaking at the right causal level of description.

This is, in fact, the same reason why Schrödinger’s cat is such an unhelpful metaphor. No one has ever given the vaguest hint at what the wavefunctions of a live and dead cat look like, and I would argue that is because “live” and “dead” can’t be expressed in quantum-mechanical terms: they are not well-defined quantum states.

I don’t necessarily argue that this rescues Kevin’s idea that quantum indeterminacy creates space for free will. I’m agnostic about that, because I don’t think what we generally mean by free will (which we might better call volitional behaviour) has any meaning at the quantum level, and vice versa. It’s best, I think, to explain phenomena at the conceptual/theoretical level appropriate to it. As Phil Anderson said years ago, it’s wrong to imagine that just because there’s reducibility of physical phenomena, this implies a reductive hierarchy of causation.

You’ll see very soon in Physics World why I’m thinking about this…