Eddie asked:

Newtonian mechanics tells us that the physical world at any particular moment can in principle be formulated as a differential equation with respect to time. By solving the differential equation and knowing the time of concern, one can find out or predict exactly how the world was in the past or how it will be in the future. Since we human beings are members of the physical world, our behaviours are necessarily governed by the laws of physics and thus fully predictable by the very same differential equation also. It follows that there is no such thing as free will.

However, quantum mechanics suggests by contrast that the physical world (the subatomic world be exact) is probabilistic with uncertainties.

Should mind-body dualism be rejected, will quantum mechanics be an essential clue for explaining the existence of free will?

Answer by Geoffrey Klempner

Let me first state something obvious. The ‘equation’ which you talk about ‘solving’ may indeed have a solution in principle, but it is not one that we can ever discover because all measurement in science has a degree of imprecision. To actually solve the equation one would need to have precise values, for even the smallest deviation will be magnified over time (the ‘butterfly effect’).

However, this leads to a second obvious point. There is a crucial difference for us, as human beings facing an uncertain future, between a universe in which the future is all laid out, determinately, even if we cannot know or predict it – where every event happens because of, say, the precise way that the Big Bang banged – and a universe where some events can occur without a determining cause. The second universe is ‘open’ not ‘closed’. This seems to matter to us, it makes a difference to the way we strive. But, even so, this would have nothing to do with free will as such.

There are two, in some sense diametrically opposed situations where one talks of an agent ‘exercising free will’.

One type of example, which is easily neglected in discussions such as these, is where you perform an action which everyone knew you would do. Let’s say I have a passion for the free will problem so that if any question about free will comes up on Ask a Philosopher I will always try to answer it. A colleague remarks, ‘I’m surprised you bothered to answer Eddie’s question.’ ‘You should have known be better than that!’ I reply. I’m a bit annoyed that my colleague didn’t know I was so keen on the free will problem. But that didn’t make my decision to answer Eddie’s question any less of a ‘free’ decision.

The other kind of example is where a decision is finely balanced. It is at least conceivable that a quantum event in the brain could be the thing that makes you go one way, or the other. Schopenhauer, writing long before quantum theory in his ‘Prize Essay on the Freedom of the Will’, argued that the ‘freedom of indifference’, where the tiniest impulse can tip the balance one way or the other, is not true ‘freedom’, because you weren’t involved. Your character, your desires, passions, ideals, none of these were sufficient to decide the question.

And, yet, what is interesting about this example – which is very common – is that after the event when you made your decision, albeit on the flimsiest or even non-existent grounds, you will seek to rationalize it, talk about it in a way which gives the decision a meaningful place in your ongoing ‘life story’. You make the decision yours by the things you do and say subsequently.

Clearly, on this scenario, it wouldn’t make any difference whether quantum theory was true or false. Even in a determinist universe, finely balanced decisions can happen. From a subjective point of view, we wouldn’t know the difference.

The pessimistic view is that free will is impossible either way. In a deterministic universe, we are like wind-up clockwork toys. In a quantum universe we are like roulette wheels. But these are just pictures. If you allow the picture to take hold of your mind you will lose the thing you have now, which arguably is all we could want from a concept of ‘free will’.

There is a deep sense of mystery in the incompatibility between our picture of ‘how the universe works’ and our sense of our own subjective reality. We don’t know our own selves, as we are ‘objectively’, and in a sense cannot know. The free will problem is the classic expression of this.