Free Will and Physics

John Rose wrote here yesterday concerning Einstein’s attempted reconciliation of complete physical determinism and human free will, and he noted the argument, mentioned by Stephen Barr and others , that the indeterminacy of quantum theory may make a place for free will in the physical universe.

Without disagreeing with either Rose or Barr, I would note that, even if it turns out that the physical universe is completely deterministic, we ought have no worries about free will. I say this not because I am a “soft determinist,” thinking that physical determinism is compatible with any coherent account of free will, but because I am prepared to say that a human being is not a purely physical system. Indeed, I think anyone who believes in an immortal spiritual soul that survives the death of the body is committed to saying just this. But if a human being is not a purely physical system, there is no reason to think that everything that human beings do happens in accordance with the laws of physics, whether those laws be deterministic or otherwise. In other words, if tomorrow it were conclusively established that the laws of physics are fully deterministic, I would say that human beings, being not purely physically systems, often do things that violate those laws.

Some people who argue that quantum indeterminacy makes room for free will do so because they are bothered by the idea that something outside of physical reality¯the spiritual soul¯might be affecting physical reality and causing physical things to behave otherwise than the laws of physics entail. This is a genuine concern, for the mechanism for such interaction between the spiritual and the physical is, to say the least, highly mysterious. (Descartes theorized that the interaction took place at the pineal gland deep inside the brain.)

Some people appealing to quantum indeterminacy think they can side-step such problems because they can affirm both that human beings act freely and that human beings act always in accordance with the laws of physics. This, however, is an illusion. They in no way avoid the problem of a nonphysical reality affecting the physical world, because it’s implicit in their view that the nonphysical reality (whether they think of it as a spiritual soul or otherwise) is causing a quantum indeterminacy to be resolved one way rather than another¯more precisely, is causing a wave function to collapse. On their view, the human soul amounts to a hidden variable.

I thus do not see why cramming human free will into quantum indeterminacy seems attractive. Such a view does not avoid the problem of explaining how a spiritual reality affects physical realities, and it also creates the strange anomaly that quantum indeterminacies inside the human brain are resolved by acts of free will by the spiritual soul but quantum indeterminacies everywhere else in the universe are resolved in some other way.

Moreover, there are powerful philosophical arguments unrelated to free will supporting the proposition that human beings are not purely physical systems (for example, arguments that purely physical systems cannot have intellectual content¯cannot be the subject of predicates such as “believes it will rain next Tuesday” or “hopes to be admitted to Yale in the fall”). It is much easier, in my view, to say that human beings, not being purely physical systems, sometimes act contrary to the laws of physics, and so be done with it.

Robert T. Miller is an assistant professor at the Villanova University School of Law.