The quantum mind or quantum consciousness hypothesis proposes that classical mechanics cannot explain consciousness, while quantum mechanical phenomena, such as quantum entanglement and superposition, may play an important part in the brain's function, and could form the basis of an explanation of consciousness. It is not one theory, but a collection of distinct ideas described below.
A few theoretical physicists have argued that classical physics is intrinsically incapable of explaining the holistic aspects of consciousness, whereas quantum mechanics can. The idea that quantum theory has something to do with the workings of the mind go back to Eugene Wigner, who assumed that the wave function collapses due to its interaction with consciousness. However, modern physicists and philosophers consider the arguments for an important role of quantum phenomena to be unconvincing. 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 philosopher David Chalmers has argued against quantum consciousness. He has discussed how quantum mechanics may relate to dualistic consciousness. Indeed, Chalmers is skeptical of the ability of any new physics to resolve the hard problem of consciousness.
Description of main quantum mind approaches
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 he formulated in terms of a quantum field theory. This more fundamental level was proposed to represent an undivided wholeness and an implicate order, from which arises 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.
Roger Penrose and Stuart Hameroff
|This section relies on references to primary sources. (February 2012)|
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 collaborated to produce Orch-OR in the early 1990s.
Penrose's controversial argument began from Gödel's incompleteness theorems. In his first book on consciousness, The Emperor's New Mind (1989), he argued that while a formal proof system cannot prove its own inconsistency, Gödel-unprovable results are provable by human mathematicians. He takes this disparity to mean that human mathematicians are not describable as formal proof systems, and are not therefore running a computable algorithm.
Penrose determined that wave function collapse was the only possible physical basis for a non-computable process. Dissatisfied with its randomness, Penrose proposed a new form of wave function collapse that occurred in isolation, called objective reduction. He suggested that each quantum superposition has its own piece of spacetime curvature, and when these become separated by more than one Planck length, they become unstable and collapse. Penrose suggested that objective reduction represented neither randomness nor algorithmic processing, but instead a non-computable influence in spacetime geometry from which mathematical understanding and, by later extension, consciousness derived.
Originally, Penrose lacked a detailed proposal for how quantum processing could be implemented in the brain. However, Hameroff read Penrose's work, and suggested that microtubules would be suitable candidates.
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. Hameroff originally suggested the tubulin-subunit electrons would form a Bose-Einstein condensate, but this was discredited. He then proposed a Frohlich condensate, a hypothetical coherent oscillation of dipolar molecules. However, this too has been experimentally discredited.
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 to non-computationally access mathematical understanding and ultimately conscious experience, that are hypothetically embedded in the geometry of spacetime.
However, Orch-OR makes numerous false biological predictions, and is considered to be an extremely poor model of brain physiology. The proposed predominance of 'A' lattice microtubules, more suitable for information processing, was falsified by Kikkawa et al., who showed that all in vivo microtubules have a 'B' lattice and a seam. The proposed existence of gap junctions between neurons and glial cells was also falsified. Orch-OR predicts that microtubule coherence reaches the synapses via dendritic lamellar bodies (DLBs), however De Zeeuw et al. proved this impossible, by showing that DLBs are located micrometers away from gap junctions.
Umezawa, Vitiello, Freeman, Kak
Hiroomi Umezawa and collaborators proposed a quantum field theory of memory storage. Giuseppe Vitiello and Walter Freeman have proposed a dialog model of the mind, where this dialog takes place between the classical and the quantum parts of the brain. Quantum field theory models of brain dynamics are fundamentally different from the Penrose-Hameroff theory. Subhash Kak has proposed that the physical substratum to neural networks has a quantum basis, but he also points out that the quantum mind will still have machine-like limitations.
Henry Stapp favors the idea that quantum waves are reduced only when they interact with consciousness. He argues from the Copenhagen Interpretation that the quantum state collapses when the observer selects one among the alternative quantum possibilities as a basis for future action. The collapse, therefore, takes place in the expectation that the observer associated with the state.
His theory of how mind may interact with matter via quantum processes in the brain differs from that of Penrose and Hameroff.
Criticism by Max Tegmark
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.
- Bohm interpretation of quantum mechanics
- Quantum mind–body problem
- Quantum cognition
- Electromagnetic theories of consciousness
- Evolutionary neuroscience
- Hard problem of consciousness
- Holonomic brain theory
- Mechanism (philosophy)
- Hameroff-Penrose Orchestrated Objective Reduction
- Theory of mind
- John Searle (1997). The Mystery of Consciousness. The New York Review of Books. pp. 53–88. ISBN 978-0-940322-06-6.
- Stenger, Victor, "The Myth of Quantum Consciousness", The Humanist Vol 53 No 3 (May–June 1992) pp. 13-15 
- David J. Chalmers (2003). "Consciousness and its Place in Nature". In Stephen P. Stich & Ted A. Warfield. Blackwell Guide to Philosophy of Mind. Blackwell. ISBN 978-0-631-21774-9.
- David J. Chalmers (1995). "Facing Up to the Problem of Consciousness". Journal of Consciousness Studies 2 (3): 200–219.
- David J. Chalmers (1997). The Conscious Mind: In Search of a Fundamental Theory. Philosophy of Mind Series. Oxford University Press. ISBN 978-0-19-511789-9.
- David Bohm (1980). Wholeness and the Implicate Order. London: Routledge. ISBN 0-203-99515-5.
- Piaget, J. (1956). The Origin of Intelligence in the Child. Routledge.
- Hameroff, Stuart (2008). "That's life! The geometry of π electron resonance clouds". In Abbott, D; Davies, P; Pati, A. Quantum aspects of life. World Scientific. pp. 403–434. Retrieved Jan 21, 2010.
- Roger Penrose & Stuart Hameroff (2011). "Consciousness in the Universe: Neuroscience, Quantum Space-Time Geometry and Orch OR Theory". Journal of Cosmology 14.
- Reimers, Jeffrey R.; McKemmish, Laura K.; McKenzie, Ross H.; Mark, Alan E.; Hush, Noel S. (17). "Weak, strong, and coherent regimes of Fröhlich condensation and their applications to terahertz medicine and quantum consciousness". PNAS 106 (11): 4219–4224. Bibcode:2009PNAS..106.4219R. doi:10.1073/pnas.0806273106. PMC 2657444. PMID 19251667. Retrieved 10 June 2013.
- Kikkawa, M., Ishikawa, T., Nakata, T., Wakabayashi, T., Hirokawa, N. (1994). "Direct visualization of the microtubule lattice seam both in vitro and in vivo". Journal of Cell Biology 127 (6): 1965–1971. doi:10.1083/jcb.127.6.1965. PMC 2120284. PMID 7806574.
- Kikkawa, M., Metlagel, Z. (2006). "A molecular "zipper" for microtubules". Cell 127 (7): 1302–1304. doi:10.1016/j.cell.2006.12.009. PMID 17190594.
- F. J. Binmöller & C. M. Müller (1992). "Postnatal development of dye-coupling among astrocytes in rat visual cortex". Glia 6 (2): 127–137. doi:10.1002/glia.440060207. PMID 1328051.
- De Zeeuw, C.I., Hertzberg, E.L., Mugnaini, E. (1995). "The dendritic lamellar body: A new neuronal organelle putatively associated with dendrodentritic gap junctions". Journal of Neuroscience 15 (2): 1587–1604. PMID 7869120.
- G. Vitiello, My Double Unveiled. John Benjamins, 2001.
- W. Freeman and G. Vitiello, Nonlinear brain dynamics as macroscopic manifestation of underlying many-body dynamics. Physics of Life Reviews, vol. 3, pp 93-118, 2006.
- S. Kak, Quantum neural computing, In Advances in Imaging and Electron Physics, vol. 94, P. Hawkes (editor). Academic Press, 1995, pp. 259-313.
- A. Gautam and S. Kak, Symbols, meaning, and origins of mind. Biosemiotics (Springer Verlag), vol. 6, 2013.
- Stapp H.P. Mindful Universe: Quantum Mechanics and the Participating Observer. Springer, 2007.
- Tegmark, M. (2000). "Importance of quantum decoherence in brain processes". Physical Review E 61 (4): 4194–4206. arXiv:quant-ph/9907009. Bibcode:2000PhRvE..61.4194T. doi:10.1103/PhysRevE.61.4194.
- Charles Seife (4 February 2000). "Cold Numbers Unmake the Quantum Mind". Science 287 (5454): 791. doi:10.1126/science.287.5454.791. PMID 10691548.
- Flanagan, Brian. Are Perceptual Fields Quantum Fields?
- Hodgson, David. The Mind Matters. Oxford University Press, 1993.
- Koch, C. and Hepp, K., "Quantum mechanics in the brain", Nature 440, 611 (30 March 2006)
- Litt et al., "Is the Brain a Quantum Computer?", Cognitive Science (2006)
- Lockwood, Michael. Mind, Brain and the Quantum. Cambridge, MA: Basil Blackwell Ltd., 1989.
- McFadden, Johnjoe (2000) Quantum Evolution HarperCollins. ISBN 0-00-255948-X; ISBN 0-00-655128-9 . Final chapter on the quantum mind.
- Pharaoh, M.C. (online). Looking to quantum mechanics for a reductive explanation of the noumenon of consciousness Retrieved June.21 2008.
- Schrödinger, Erwin. Mind and Matter. Cambridge University Press, 1959.
- Weyl, Hermann. Mind and Nature, University of Pennsylvania Press, 1934.
- Wigner, Eugene. "Physics and the Explanation of Life", in Foundations of Physics, vol. 1, 1970, pp. 34–45.
- Center for Consciousness Studies, directed by Stuart Hameroff
- Online papers on consciousness
- Stanford Univ. Encyclopedia of Philosophy critical survey article Harald Altmanspacher (2006) Quantum Approaches to Consciousness
- "What is an Essentially Quantum Mechanical Effect?", Osvaldo Pessoa Jr.