Could quantum mechanics save the soul? In the light of 20th century physics, is free will plausible?

Such as been the hope of some philosophers, scientists (and pretenders to those titles) – but neuroscientist Peter Clarke argues that it’s just not happening, in an interesting new paper: Neuroscience, quantum indeterminism and the Cartesian soul

Clarke first outlines the dualism of Rene Descartes, who famously believed in an immaterial human soul separate from the brain, and responsible for rational thought. But this implied that an immaterial soul could break the laws of physics, and affect some physical processes in the brain, in order to control our actions. Even in the 17th century, this was regarded as a bit much:

Princess Elizabeth of Bohemia (oldest daughter of King James VI), wrote: “…it would be easier for me to concede matter and extension to the soul, than to concede the capacity to move a body and to be moved by it to an immaterial thing.”
But the 20th century gave new life to dualism. Quantum theory taught that physics is non-deterministic on the smallest scales; most famously, Heisenberg’s uncertainty principle states that we can’t know the exact properties of any particle for sure – only the probability of finding a certain kind of particle in a certain place.

Since then, a number of authors have argued that the soul interacts with the brain by altering the distribution of quantum states, in such a way that it alters brain function. Arguably, this would not be ‘breaking the laws of physics’ in an objectionable Cartesian way. Because, thanks to Heisenberg, there was always a chance that the system would have ended up the desired way all along.

But Clarke pours cold water on this hope:

We consider whether a fluctuation within the limits of Heisenbergian uncertainty could affect the presynaptic calcium concentration by permitting a chemical bond to be modified in an ion channel, as has been proposed…

Tinkering with presynaptic calcium channels is one of the main proposals for how souls could alter neuronal firing. However,

… even with the conservative value of a time uncertainty of 10 milliseconds, Heisenberg’s equation gives an energy uncertainty of approximately 5.2 x 10^-30 J, which is about 200,000 times too small to disrupt even a single Van der Waals interaction, the weakest kind of chemical bond…