The quantum mind hypothesis proposes that classical mechanics cannot explain consciousness, while quantum mechanical phenomena, such as quantum entanglement (two particles acting in unison) and superposition (physical systems exist partly in all their particular, theoretically possible states, but, when measured, give a result corresponding to only one of the possible configurations [decoherence]), may play an important part in the brain’s function, and could form the basis of an explanation of consciousness.

However, physicist Victor Stenger characterized quantum consciousness as a ‘myth’ having ‘no scientific basis’ that ‘should take its place along with gods, unicorns and dragons.’ The main argument against the quantum mind proposition is that quantum states in the brain would decohere before they reached a spatial or temporal scale at which they could be useful for neural processing. This argument was elaborated by the physicist, Max Tegmark. Based on his calculations, Tegmark concluded that quantum systems in the brain decohere quickly and cannot control brain function.

American quantum physicist David Bohm took the view that quantum theory and relativity contradicted one another, and that this contradiction implied that there existed a more fundamental level in the physical universe. He claimed that both quantum theory and relativity pointed towards this deeper theory, which is now understood to be quantum field theory. This more fundamental level was supposed to represent an undivided wholeness and an implicate order, from which arose the explicate order of the universe as we experience it. Bohm’s proposed implicate order applies both to matter and consciousness, and he suggests that it could explain the relationship between them. Mind and matter are here seen as projections into our explicate order from the underlying reality of the implicate order. Bohm claims that when we look at the matter in space, we can see nothing in these concepts that helps us to understand consciousness.

In trying to describe the nature of consciousness, Bohm discusses the experience of listening to music. He thinks that the feeling of movement and change that make up our experience of music derives from both the immediate past and the present both being held in the brain together, with the notes from the past seen as transformations rather than memories. The notes that were implicate in the immediate past are seen as becoming explicate in the present. Bohm views this as consciousness emerging from the implicate order. Bohm sees the movement, change or flow and also the coherence of experiences, such as listening to music as a manifestation of the implicate order. He claims to derive evidence for this from the work of Jean Piaget in studying infants. He states that these studies show that young children have to learn about time and space, because they are part of the explicate order, but have a ‘hard-wired’ understanding of movement, because it is part of the implicate order. He compares this ‘hard-wiring’ to Chomsky’s theory that grammar is ‘hard-wired’ into young human brains. In his writings, Bohm never proposed any specific brain mechanism by which his implicate order could emerge in a way that was relevant to consciousness, nor any means by which the propositions could be tested or falsified.

Theoretical physicist Roger Penrose and anaesthesiologist Stuart Hameroff collaborated to produce the theory known as Orchestrated Objective Reduction (Orch-OR). Penrose and Hameroff initially developed their ideas separately, and only later cooperated to produce Orch-OR. Penrose came to the problem from the point of view of mathematics and in particular Gödel’s incompleteness theorem (regarding the limitations of mathematical systems), while Hameroff came from a career in cancer research and anaesthesia. Gödel’s theorem is central to this theory. In 1931, Gödel proved that any theory capable of expressing elementary arithmetic cannot be both consistent and complete. Further to that, for any consistent formal theory that proves certain basic arithmetic truths there is an arithmetical statement that is true, but not provable in theory.

The theorem is not in itself controversial, but what Penrose developed from it is. In his first book on consciousness, ‘The Emperor’s New Mind’ (1989), Penrose argued that the theorem showed that the brain had the ability to go beyond what could be achieved by axioms or formal systems. He argued that this meant that the brain had some additional function that was not based on algorithms (a system of calculations), whereas a computer is driven solely by algorithms. Penrose asserted that the brain could perform functions that no computer could perform. He called this type of processing ‘non-computable.’ Penrose went on to consider what it was in the human brain that was not driven by algorithms. Given the algorithm-based nature of most of physics, he decided that the random choice of position etc. that occurs when a quantum wave collapses into a particle was the only possibility for a non-computable process. However, Penrose admitted that the randomness of the wave function collapse, although free from algorithms, is not a basis for any useful form of human understanding.

Penrose now proposed a second form of wave function collapse that could apply where quanta did not interact with the environment, but might collapse on their own accord. He suggests that each quantum superposition has its own piece of spacetime curvature, and when these become separated by more than a Planck length (microscopic distance) they become unstable and collapse. Penrose called this form of collapse objective reduction. Penrose suggested that objective reduction represented neither randomness nor the algorithm based processing of most physics, but instead a non-computable influence embedded in the fundamental level of spacetime geometry from which mathematical understanding and, by later extension of the theory, consciousness derived.

When he wrote his first book on consciousness, ‘The Emperor’s New Mind’ in 1989, Penrose lacked a detailed proposal for how quantum processing could be implemented in the brain. Subsequently, Hameroff read Penrose’s work, and suggested that microtubules (a cellular organelle) could be suitable candidates for quantum processing, an hypothesis which remains intensly controversial. Microtubules have a well established position in conventional biology and neuroscience. They are the main component of a supportive structure within neurons known as the cytoskeleton. In addition to providing a supportive structure, the known functions of microtubules include transport of molecules including neurotransmitters bound for synapses and control of the development of the cell.

Microtubules are composed of tubulin protein dimer subunits. The tubulin dimers each have hydrophobic pockets that are 8 nm apart, and which may contain delocalised pi electrons. Tubulins have other smaller non-polar regions that contain pi electron-rich indole rings separated by only about 2 nm. Hameroff proposes that these electrons are close enough to become quantum entangled. In the original version of his proposals, Hameroff went on to hypothesize that these electrons could become locked in phase, forming a state known as a Bose-Einstein condensate. In his most recent paper, he has amended this to suggest that electrons within the tubulin subunits are part of a Frohlich condensate, which is a coherent oscillation of dipolar molecules.

Furthermore, he proposes that condensates in one neuron could extend to many others via gap junctions between neurons, thus forming a macroscopic quantum feature across an extended area of the brain. When the wave function of this extended condensate collapsed, it was suggested that this could give access to non-computational influences related to mathematical understanding and ultimately conscious experience that are embedded in the geometry of spacetime. Finally, Hameroff postulated that the activity of these condensates is the source of gamma wave synchronization in the brain. This synchronization has also been viewed as a likely correlate of consciousness in conventional neuroscience, and it has been shown to be linked to the functioning of gap junctions.

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