Quantum Leaps in Philosophy of Mind

David Bourget

University of Toronto

Journal of Consciousness Studies, 11, 12, 2004, pp. 17-42

In this article, David Bourget attacks Stapp’s theory of quantum consciousness. First he discusses some of the difficulties posed by quantum theory itself. He regards von Neumann’s 1955 version as the final version of the orthodox view of quantum theory. This distinguishes the collapse of the quantum wave from the evolution of the wave. The collapse of the wave is here related to a measurement. The evolution of a system subject to a measurement is termed a projection postulate. It is not deterministic, in that the state that the system evolves into is not determined by the current state which is the wave function. However, probabilities can be assigned to the various possible outcomes. Stapp refers to these types of measurement as empirical questions. The questions have to have yes or no answers in response to questions about observables, such as ‘is the particle at position P’?

In contrast to the actual collapse of the wave function, the evolution of the wave is determined by Schrödinger’s equation, and specifies deterministically what state the system will be in in the future providing no measurement takes place. This system represents a superposition of states that an observable could be in.

What the theory does not define is what processes occur when the wave function collapses. The theory does not state when a measurement should occur. It is left to the mind of an experimenter to decide the timing, make the measurement, and apply the projection postulate. Nor does the theory specify what type of measurement should be made. This is again left to the mind of the experimenter, but the choice of type of measurement has an important impact on the future development of the system. In the orthodox theory there is also a problem as to where the collapse takes place between an original photon collision and the subsequent neural events in an observers mind.

Stapp, who claims to follow Heisenberg’s interpretation, sees the collapse of the wave function as a real event, which draws a dividing line between the potentials of the quantum world and the objects of the classical world.


Stapp criticises the classical view of freewill, because it leaves no room for the conscious will to determine actions. The universe would be no different if it did not exist in the view of classical physics. He favours a theory that frees the will from domination by the lowest level of physical objects, which is what happens in the classical theory, and he looks to quantum theory for an explanation.

Stapp’s original view of how free will functioned in the brain drew on the ideas of Eccles (1994)(1). This relates to the release of neurotransmitters from the boutons at the end of axons. The bouton contains vesicles holding neurotransmitters. A nerve impulse, or fluctuation in electrical potential in the axon, causes an influx of calcium ions into the bouton, which set off a process that triggers a release of neurotransmitters into the synaptic cleft. Eccles pointed out that normally only one vesicle released its neurotransmitters, although there could be as many as 50 vesicles potentially able to release neurotransmitters. Eccles suggested that the mind exerted control at the quantum level by tuning the grid that holds the vesicles.

Stapp suggests that the calcium ions could be in superposition. However, Bourget thinks that if indeterminancy did arise at individual synapses they would average out across the brain. Stapp, however, thinks that indeterminacies could be amplified across the brain into large patterns. He envisages self-sustaining neural groups driven by these indeterminacies. Eventually the strongest signal is extracted from competing signals, so the original intervention of the mind at the neurotransmitter level can be amplified up. The choice open to the mind is to choose which probability emerges from the wave function collapse, but it cannot specify anything else in this theory.

Bourget claims that Stapp altered his view of freewill during the 1990’s According to Bourget, it is only in the later versions of his theory that Stapp says that freewill is not involved in the collapse of the wave function, but only in the inderterminacies of quantum measurement. Stapp thinks that the indeterminancies as to the timing of a quantum measurement leave scope for freewill. Stapp sees the freedom of the will as limited to asking or not asking a particular question, such as ‘am I moving a finger? The frequency with which the will asks questions of the system can alter the dynamics of the brain system. (Misra and Sudarshan 1977) (Joos, 1996) (Itano et al 1990) (2-4).

The Unity of Consciousness

Stapp concentrates on the unity of consciousness. He thinks that this requires a physical correlate that does not exist in classical physics. Stapp relates this to quantum non-locality, where the collapse of the wave function of one particle, decides the outcome of the collapse of another, even though the latter is out of range of a signal travelling at the speed of light, or any other physical contact. Because of its unity, consciousness cannot be seen as the action of separate particles, but as holistic collpases over large parts of the brain.

Stapp defines our experience of consciousness as the feeling of events in the top-level processing of the brain. Qualia are defined as non-decomposable patterns of neural activity, while intentional states are seen as combinations of such patterns. Stapp draws a distinction between qualia such as the redness of red, the elemental or absolute units of experience and the meanings or intentional states that arise from the basic units of qualia.

Bourget considers that decoherence may present a problem for Stapp’s theory. He points out that the brain, in Stapp’s theory, seems to wander between the superposed yes and no answers to questions until freewill holds it onto either a yes or a no answer. Bourget thinks that Stapp’s account implies superpositions not only of brain macrostates but of their environment.


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