If there is one thing that religions absolutely must believe in, it is the existence of the soul, although not all religions give it the same name. Without the belief that there is some entity that is part of us and yet somehow independent of the body and can interact freely with an external deity, much of religious doctrine becomes even more vacuous than it currently is.
But how can the freely acting (Cartesian) soul exist in a world governed by scientific laws? One favored option is to use Heisenberg’s quantum indeterminancy as a mechanism, suggesting that it provides a loophole to escape determinism. This effect is tiny but some religious people who are also scientists (like Ken Miller) pin their hopes on it.
But a new paper by P. G. Clarke titled Neuroscience, quantum indeterminism and the Cartesian soul that appeared in the journal Brain and Cognition (2014 Feb;84(1):109-17) adds to the drubbing that the soul has been getting lately. Here’s the abstract.
Quantum indeterminism is frequently invoked as a solution to the problem of how a disembodied soul might interact with the brain (as Descartes proposed), and is sometimes invoked in theories of libertarian free will even when they do not involve dualistic assumptions. Taking as example the Eccles–Beck model of interaction between self (or soul) and brain at the level of synaptic exocytosis, I here evaluate the plausibility of these approaches. I conclude that Heisenbergian uncertainty is too small to affect synaptic function, and that amplification by chaos or by other means does not provide a solution to this problem. Furthermore, even if Heisenbergian effects did modify brain functioning, the changes would be swamped by those due to thermal noise. Cells and neural circuits have powerful noise-resistance mechanisms, that are adequate protection against thermal noise and must therefore be more than sufficient to buffer against Heisenbergian effects. Other forms of quantum indeterminism must be considered, because these can be much greater than Heisenbergian uncertainty, but these have not so far been shown to play a role in the brain.
In short, he says that in order for neuronal cells to be able to function they have to be able to overcome the disruption of thermal vibrations (that are always present). But these same noise suppression mechanisms will also suppress the much smaller effects of indeterminancy, even if they are amplified by some chaotic mechanism. In order that its signals not be disrupted randomly, the brain has developed a pretty good thermal noise-resistance mechanism.
Every cell in the body is constantly subject to thermal noise – thermally driven molecular movements – and is resistant to its effects. Thermal noise causes significant fluctuations in many cellular events including transcription and translation (“gene expression noise”), ion channel permeability (“channel noise”) and synaptic function (“synaptic noise”). Individual cells and brain function as a whole both have numerous inbuilt noise-resistance mechanisms including mass action, negative feedback and frequency-selective feedback, as I have discussed in detail in a recent review (Clarke, 2012). Thermal noise can be considered random in the sense that it is not biologically controlled or coordinated in any way with cellular function, but is on a sufficiently large scale to be describable by classical (deterministic) physics. This constitutes a fundamental problem for hypotheses of soul-mind interaction based on quantum-scale phenomena, because a neuron (or neural circuit etc.) whose function is resistant to thermal noise should a fortiori be resistant to the much smaller perturbations of quantum phenomena.
The conclusions of this study also raises problems for a free-standing consciousness or free-will in the classical sense. The author seems a little uncomfortable with that and suggests that there may be a way to reconcile those with his work.
The present paper raises problems for attempts to ground notions of a Cartesian soul (or self etc.) or free will on Heisenbergian uncertainty, because the uncertainty is too small in absolute terms and – even more importantly – in relation to the deterministic, but biologically uncontrolled, disruptions due to thermal noise. Moreover neurons and neural circuits have a built-in resistance to the thermal noise, and it seems unlikely that the smaller effects of Heisenbergian uncertainty could overcome the powerful noise-resistance mechanisms.
Even though I raise difficulties for attempts to ground notions of a Cartesian soul (or self) and free will in quantum indeterminacy (Heisenbergian or other), I do not consider that rejection of this particular grounding need undermine the notions of selfhood and free will, because moderate versions of physicalism such as dual aspect theory, and a compatibilist approach to free will provide alternative groundings.
I don’t know that I buy this. You can read more about this study here.