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Does Quantum Physics have a Role in the Mind-Brain System?

An Introduction

The problem of the relation between mind and body is well known as a difficult `world knot'. Over the centuries various monistic and dualistic theories have been proposed, and the subject has had renewed interest as we try to assimilate the implications of quantum physics. These implications may make us reexamine our views of brains and bodies, but it is still not clear what consequences they have for our understanding of minds.  We may suspect that quantum mechanics and consciousness are related, but the details are not at all clear.

Measurements and Consciousness

Earlier in the interpretation of quantum mechanics, it appeared that the problem of measurement could only be solved by introducing some basic notion of an observer, presumably a conscious observer. Many scientists and philosophers (e.g. Wigner (1962) Eccles and Popper (1977), Faber (1986), Toben (1974), Squires (1990), Donald (1990) among others) have taken this solution to indicate an essential role of consciousness in the physical world. Consciousness, to solve the measurement problem, must initiate the transition from quantum potentialities to definite actualities. It would not have to select which actuality, but merely cause some actuality to be produced. Squires and Donald accept this merely `collapse prompting' role of consciousness, and their position has the advantage of requiring no changes to quantum theory, as consciousness then makes no change to any predicted probability. Squire's conclusion, unfortunately, does not yield any functional role which may be important in mental and/or physiological processes in the brain. Donald (1990) does go on to give circumstances in which `measurement collapses' are important for the function of neural cells, but their effects are simply to reinstate the `classical' on/off nature of the sodium switches even when there are quantum uncertainties. 

Since, moreover, it is possible that the `measurement problem' can be solved within physics (see e.g. Maxwell, 1988), the role of consciousness in measurement has little direct bearing on the problem of how the mind and brain function together. In order to say something relevant to the brain sciences, we have to go beyond conventional quantum mechanics (of whatever interpretation), and make new hypotheses with definite empirical content. We have to postulate that `consciousness' (whatever that may turn out to be) influences the actual outcome of neural events, and does not just observe them as if disinterestedly. 

Quantum Brains

It is well known that there is a residual indeterminism of quantum mechanics in making predictions of physical processes. Quantum mechanics is also `non-local', as described for example by Bell's inequalities. If either of these two phenomena are displayed in the brain as described by quantum physics, then this may be relevant to the problem of consciousness. 

Biased Probabilities:

One proposal (from Walker (1970) and later Eccles (1977)) has been that mental events influence at least some physical outcomes within the range allowed by quantum mechanics. This idea has to supplemented by an account of how these small effects are amplified to affect macroscopic outcomes, and recently possible accounts have been presented, Eccles (1989). Eccles requires that the options of a single vesicle discharging or not discharging both have non-zero quantum probabilities, so that such neural events are genuinely under-determined by quantum mechanics, and the way is open for them to be determined by the mind. 

Bose-Einstein Condensates:

Another proposal by Marshall (1989) is that the mental and bodily realms derive directly from a quantum realm, as separate appearances of an underlying structure given by quantum mechanics. Since the unity of mental experience is one of its outstanding features, the proposal is that consciousness arises from a quantum mechanical structure which shows remarkably unity, namely Bose-Einstein condensates. This therefore requires not only that the brain amplifies quantum indeterminism, but also that long-range and long-time correlations of quantum phases are set up in the brain, by means for example of a structure proposed by Fröhlich. 

Both these proposals go some way toward connecting the apparently disparate realms of mind and brain. From the physics side, both have quantum mechanics holding virtually unchanged. They furthermore then both require that neuro-physiological processes are in some essential way `quantum processes'. They require then that the peculiarly quantum features of matter become much more spatially spread out in the brain than is usually admitted. In the language of physics, Marshall requires that non-local correlations (of the kind described by Bell's Inequalities) are set up between parts of the brain that are very far apart on the atomic scale, and hence that the brain exhibits some of the characteristics of `quantum computers' as described by Deutsch (1985). There is a difficulty that this implies much larger quantum effects than have ever been observed in materials at room temperature. There is evidence of unusual microwave absorption, but it is not clear whether this really demonstrates quantum correlations as distinct from sets of coupled classical (non-quantum) oscillations. 

Eccles' proposal is weaker than Marshall's, as he only requires that for some brief time the non-local correlations extend between the options of a single vesicle discharging or not discharging, so there can exist a coherent superposition of these two states. Eccles does not require that the two options remain coherent for any duration after the event (as Marshall would require to obtain widespread and persisting quantum phase coherences). 

Both proposals are made less likely by the fact that Plank's constant, which sets the scale for quantum processes, is so small. It is not impossible that there are genuinely undetermined neural events in the brain, and/or that there are large scale quantum coherent effects, but these are difficult to set up in the noisy room-temperature non-crystalline system of the brain.

Psychological Considerations.

There are also questions from the psychological point of view. Eccles' proposal tells us very little about the structure of the mind, apart from the fact that it must be able to predict and control the amazingly complicated system of many of the random discharges in the brain. There is little indication from what psychologists know about the mind that it has anything like the required analytical and motor capacities. The mind is best dealing with at most 5 to 8 items, and is completely swamped when it tries to understand massively parallel systems directly. A way of avoiding these difficulties will be discussed later

Marshall's proposal seems to tell us more about the mind, namely that it arises whenever quantum mechanics gives suitable Bose-Einstein condensates. However, all psychological details of mental structure and operations would then be derived from this quantum structure. That is, he would have to claim that all human life (from mathematics and logic to arts to psychopathology) is implicit in Schrödinger's equation. Personally, I find it extremely implausible that the quantum mechanics of patterns of excitations of Bose-Einstein condensates exactly and mechanically determines the interaction patterns of ideas, images and meanings in the human mind. There are certainly similarities between the two, but these do not imply identity. To talk of similarity without giving evidence for identity leads to another approach, as we see next


  • Deutsch, D. (1985) `Quantum Theory, the Church-Turing principle and the universal quantum computer', Proc. R. Soc. Lond, A 400, pp. 91 - 117.
  • Donald, M.J. (1990) `Quantum Theory and the Brain', Proc. R. Soc. Lond, A 427, pp. 43 - 93.
  • Eccles, J. and K.R. Popper, (1977) `The Self and Its Brain', Springer.
  • Eccles, J. (1989) `Evolution of the Brain: Creation of the Self', Routledge.
  • Faber, R.J. (1986) `Clockwork Garden'.
  • Marshall, I.N. (1989) `Consciousness and Bose-Einstein Condensates', New Ideas in Psychology, 7 pp. 73 - 85.
  • Maxwell, N. (1988) `Quantum Propensiton Theory: A testable resolution of the wave-particle dilemma', The British Journal for the Philosophy of Science, 39, pp. 1 - 50.
  • Squires, E.J. (1990) `An Attempt to Understand the Many-worlds Interpretation of Quantum Theory', in Quantum Theory without Reduction, ed. Cini and Levy-Blond, Adam Hilger, pp. 151 - 160.
  • Walker, E.H. (1970) `The Nature of Consciousness', Mathematical Biosciences, 7, pp. 131 - 178.
  • Wigner, E. (1962) `Remarks on the Mind-Body Question', pp. 284 - 302 in The Scientist Speculates, I.J. Good, ed: Basic Books, N.Y.

See also Pierro Scaruffi, 'Thinking About Thought', 2001.


Author: Ian Thompson, IJT@newdualism.org  

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