Editing Orchestrated objective reduction

{{Short description|Theory of a quantum origin of consciousness}}
{{Use dmy dates|date=May 2024}}{{multiple image|total_width=300
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| image1 = Roger Penrose 9671.JPG
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| footer = The founders of the theory: [[Roger Penrose]] and [[Stuart Hameroff]], respectively}}

'''Orchestrated objective reduction''' ('''Orch OR''') is a theory postulating that [[consciousness]] originates at the [[Quantum mind|quantum level]] inside [[neurons]] (rather than being a product of [[Neural pathway|neural connections]]). The mechanism is held to be a [[quantum physics|quantum]] process called [[objective reduction]] that is orchestrated by cellular structures called [[microtubule]]s. It is proposed that the theory may answer the [[hard problem of consciousness]] and provide a mechanism for [[free will]].<ref name=frontiers>{{cite journal |doi=10.3389/fnint.2012.00093 |pmid=23091452 |pmc=3470100 |title=How quantum brain biology can rescue conscious free will |journal=Frontiers in Integrative Neuroscience |volume=6 |pages=93 |year=2012 |last1=Hameroff |first1=Stuart |doi-access=free }}</ref> The hypothesis was first put forward in the early 1990s by [[Nobel Prize|Nobel]] laureate for [[physics]] [[Roger Penrose]], and [[Anesthesiologist|anaesthesiologist]] [[Stuart Hameroff]]. The hypothesis combines approaches from [[molecular biology]], [[neuroscience]], [[pharmacology]], [[philosophy]], [[quantum information theory]], and [[quantum gravity]].<ref name=H&PvsReimers2014>{{cite journal |doi=10.1016/j.plrev.2013.11.013 |title=Reply to seven commentaries on "Consciousness in the universe: Review of the 'Orch OR' theory"|journal=Physics of Life Reviews |volume=11 |issue=1 |pages=94–100 |year=2014 |last1=Hameroff |first1=Stuart |last2=Penrose |first2=Roger |bibcode=2014PhLRv..11...94H}}</ref><ref name="Penrose2014">{{cite journal |doi=10.1007/s10701-013-9770-0 |title=On the Gravitization of Quantum Mechanics 1: Quantum State Reduction |journal=Foundations of Physics |volume=44 |issue=5 |pages=557–575 |year=2014 |last1=Penrose |first1=Roger |bibcode=2014FoPh...44..557P|s2cid=123379100 |doi-access=free }}</ref>

While some other theories assert that consciousness emerges as the complexity of the [[computation]]s performed by [[cerebral cortex|cerebral]] [[neuron]]s increases,<ref name="McCulloch1943">{{cite journal | last1 = McCulloch | first1 = Warren S. | author1-link = Warren Sturgis McCulloch | last2 = Pitts | first2 = Walter | author2-link = Walter Pitts | title = A logical calculus of the ideas immanent in nervous activity | journal = Bulletin of Mathematical Biophysics | volume = 5 | issue = 4 | pages = 115–133 | year = 1943 | doi = 10.1007/bf02478259}}</ref><ref name="Hodgkin1952">{{cite journal | last1 = Hodgkin | first1 = Alan L. | author1-link = Alan Lloyd Hodgkin | last2 = Huxley | first2 = Andrew F. | author2-link = Andrew Fielding Huxley | title = A quantitative description of membrane current and its application to conduction and excitation in nerve | journal = Journal of Physiology | volume = 117 | issue = 4 | pages = 500–544 | year = 1952 | doi = 10.1113/jphysiol.1952.sp004764 | pmid = 12991237 | pmc = 1392413}}</ref> Orch OR posits that consciousness is based on [[Computability theory|non-computable]] [[quantum computing|quantum processing]] performed by [[qubits]] formed collectively on cellular microtubules, a process significantly amplified in the neurons. The qubits are based on oscillating [[dipoles]] forming [[Quantum superposition|superposed]] resonance rings in helical pathways throughout lattices of microtubules. The oscillations are either electric, due to charge separation from [[London forces]], or magnetic, due to [[electron spin]]—and possibly also due to [[nuclear spin]]s (that can remain isolated for longer periods) that occur in [[gigahertz]], [[megahertz]] and [[kilohertz]] frequency ranges.<ref name=H&PvsReimers2014/><ref name=HameroffVs7Others2014>{{cite journal |doi=10.1016/j.plrev.2013.11.014 |title=Reply to criticism of the 'Orch OR qubit' – 'Orchestrated objective reduction' is scientifically justified |journal=Physics of Life Reviews |volume=11 |issue=1 |pages=104–112 |year=2014 |last1=Hameroff |first1=Stuart |last2=Penrose |first2=Roger |bibcode=2014PhLRv..11..104H }}</ref> Orchestration refers to the hypothetical process by which connective proteins, such as [[microtubule-associated protein]]s (MAPs), influence or orchestrate qubit [[wave-function collapse|state reduction]] by modifying the spacetime-separation of their superimposed states.<ref name="Penrose-Hameroff2014">{{cite journal |doi=10.1016/j.plrev.2013.08.002 |pmid=24070914 |title=Consciousness in the universe |journal=Physics of Life Reviews |volume=11 |issue=1 |pages=39–78 |year=2014 |last1=Hameroff |first1=Stuart |last2=Penrose |first2=Roger |bibcode=2014PhLRv..11...39H |doi-access=free }}</ref> The latter is based on [[Penrose interpretation|Penrose's objective-collapse theory]] for interpreting quantum mechanics, which postulates the existence of an objective threshold governing the collapse of [[quantum state]]s, related to the difference of the [[spacetime curvature]] of these states in the universe's [[Planck scale|fine-scale]] structure.<ref>{{cite web |title=Physicists Eye Quantum-Gravity Interface |author=Natalie Wolchover |date=31 October 2013 |website=Quanta Magazine |type=Article |publisher=Simons Foundation |url=https://www.simonsfoundation.org/quanta/20131107-physicists-eye-quantum-gravity-interface/ |access-date=19 March 2014}}</ref>

Orchestrated objective reduction has been criticized from its inception by mathematicians, philosophers,<ref name=Boolos_1990>{{cite journal | last1 = Boolos | first1 = George | author-link = George Boolos | display-authors = etal | year = 1990 | title = An Open Peer Commentary on The Emperor's New Mind. | journal = Behavioral and Brain Sciences | volume = 13 | issue = 4| page = 655 | doi = 10.1017/s0140525x00080687 | s2cid = 144905437 }}</ref><ref name=martin_1993>{{cite journal |last1=Davis |first1=Martin |title=How subtle is Gödel's theorem? More on Roger Penrose |journal=Behavioral and Brain Sciences |date=September 1993 |volume=16 |issue=3 |pages=611–612 |doi=10.1017/S0140525X00031915 |s2cid=144018337 }}</ref><ref name=lewis_1969>{{cite journal |last1=Lewis |first1=David |title=Lucas against Mechanism |journal=Philosophy |date=July 1969 |volume=44 |issue=169 |pages=231–233 |doi=10.1017/s0031819100024591 |s2cid=170411423 |doi-access=free }}</ref><ref name=putnam_1995>{{cite journal |last1=Putnam |first1=Hilary |title=Book Review: Shadows of the mind |journal=Bulletin of the American Mathematical Society |date=1 July 1995 |volume=32 |issue=3 |pages=370–374 |doi=10.1090/S0273-0979-1995-00606-3 |doi-access=free }}</ref><ref>{{cite news |last1=Putnam |first1=Hilary |title=The Best of All Possible Brains? |url=https://archive.nytimes.com/www.nytimes.com/books/97/04/27/nnp/17540.html |work=The New York Times |date=20 November 1994 }}</ref> and scientists.<ref name=Tegmark2000>{{cite journal|doi=10.1103/PhysRevE.61.4194|title=Importance of quantum decoherence in brain processes|journal=Physical Review E|volume=61|issue=4|pages=4194–4206|year=2000|last1=Tegmark|first1=Max|bibcode=2000PhRvE..61.4194T|arxiv=quant-ph/9907009|pmid=11088215|s2cid=17140058}}</ref><ref name=Koch2006>{{cite journal |doi=10.1038/440611a |pmid=16572152 |title=Quantum mechanics in the brain |journal=Nature |volume=440 |issue=7084 |pages=611 |year=2006 |last1=Koch |first1=Christof |last2=Hepp |first2=Klaus |bibcode=2006Natur.440..611K |s2cid=5085015 |doi-access=free }}</ref><ref name=Hepp2012>{{cite journal |last1=Hepp |first1=K. |title=Coherence and decoherence in the brain |journal=Journal of Mathematical Physics |date=September 2012 |volume=53 |issue=9 |pages=095222 |doi=10.1063/1.4752474 |bibcode=2012JMP....53i5222H }}</ref> The criticism concentrated on three issues: Penrose's interpretation of [[Gödel's incompleteness theorems|Gödel's theorem]]; Penrose's [[abductive reasoning]] linking non-computability to quantum events; and the brain's unsuitability to host the quantum phenomena required by the theory, since it is considered too "warm, wet and noisy" to avoid [[decoherence]].

==Background==
{{further|Penrose–Lucas argument}}
In 1931, mathematician and logician [[Kurt Gödel]] proved that any [[effective procedure|effectively generated]] theory capable of proving basic arithmetic cannot be both [[consistency|consistent]] and [[completeness (logic)|complete]]. In other words, a mathematically sound theory lacks the means to prove itself.<ref>{{Harvnb|Hofstadter|1979|pp=476–477}}, {{Harvnb|Russell|Norvig|2003|p=950}}, {{Harvnb|Turing|1950}} under "The Argument from Mathematics" where he writes "although it is established that there are limitations to the powers of any particular machine, it has only been stated, without sort of proof, that no such limitations apply to the human intellect."</ref> In his first book concerning consciousness, ''[[The Emperor's New Mind]]'' (1989), [[Roger Penrose]] argued that equivalent statements to "Gödel-type propositions" had recently been put forward.<ref name=Penrose1989/>

Partially in response to Gödel's argument, the [[Penrose–Lucas argument]] leaves the question of the physical basis of non-[[Computable function|computable]] behaviour open. Most physical laws are computable, and thus algorithmic. However, Penrose determined that [[wave function collapse]] was a prime candidate for a non-computable process. In [[quantum mechanics]], particles are treated differently from the objects of [[classical mechanics]]. Particles are described by [[wave function]]s that evolve according to the [[Schrödinger equation]]. Non-stationary wave functions are [[linear combination]]s of the [[eigenstate]]s of the system, a phenomenon described by the [[superposition principle]]. When a quantum system interacts with a classical system—i.e. when an [[observable]] is measured—the system appears to [[wave function collapse|collapse]] to a random eigenstate of that observable from a classical vantage point.

If collapse is truly random, then no process or algorithm can deterministically predict its outcome. This provided Penrose with a candidate for the physical basis of the non-computable process that he hypothesized to exist in the brain. However, he disliked the random nature of environmentally induced collapse, as randomness was not a promising basis for mathematical understanding. Penrose proposed that isolated systems may still undergo a new form of wave function collapse, which he called objective reduction (OR).<ref name="Penrose-Hameroff2014"/>

Penrose sought to reconcile [[general relativity]] and quantum theory using his own ideas about the possible structure of [[spacetime]].<ref name="Penrose1989">{{Cite book |last=Penrose |first=Roger |title=The Emperor's New Mind: Concerning Computers, Minds and The Laws of Physics |title-link=The Emperor's New Mind |publisher=Oxford University Press |year=1989 |isbn=978-0-19-851973-7 |pages=[https://archive.org/details/emperorsnewmindc00penr/page/108/mode/2up 108–109]}}</ref>{{Page needed|date=May 2024}}<ref name= Penrose1994>{{Cite book |last=Penrose |first=Roger |author-link=Roger Penrose |title=Shadows of the Mind: A Search for the Missing Science of Consciousness |url=https://archive.org/details/shadowsofmindsea00penr_0/ |publisher=Oxford University Press |year=1989 |pages=416–7, 457 |isbn=978-0-19-853978-0 }}</ref> He suggested that at the [[Planck scale]] curved spacetime is not continuous, but discrete. He further postulated that each separated [[quantum superposition]] has its own piece of [[spacetime curvature]], a blister in spacetime. Penrose suggests that gravity exerts a force on these spacetime blisters, which become unstable above the Planck scale of <math>10^{-35} \text{m}</math> and collapse to just one of the possible states. The rough threshold for OR is given by Penrose's indeterminacy principle:
::<math>\tau \approx \hbar/E_G</math>
:where:
::* <math>\tau</math> is the time until OR occurs, 
::* <math>E_G</math> is the gravitational self-energy or the degree of spacetime separation given by the superpositioned mass, and
::* <math>\hbar</math> is the [[reduced Planck constant]]. 
Thus, the greater the mass–energy of the object, the faster it will undergo OR and vice versa. [[Mesoscopic physics|Mesoscopic]] objects could collapse on a timescale relevant to neural processing.<ref name="Penrose-Hameroff2014"/>{{additional citation needed|date=May 2013 |reason=Search for supporting evidence besides the papers from the main authors of the theory.}}

An essential feature of Penrose's theory is that the choice of states when objective reduction occurs is selected neither randomly (as are choices following wave function collapse) nor algorithmically. Rather, states are selected by a "non-computable" influence embedded in the [[Planck]] scale of spacetime geometry. Penrose claimed that such information is [[Platonism|Platonic]], representing pure mathematical truths, which relates to Penrose's ideas concerning the three worlds: the physical, the mental, and  the Platonic mathematical world. In ''[[Shadows of the Mind]]'' (1994), Penrose briefly indicates that this Platonic world could also include aesthetic and ethical values, but he does not commit to this further hypothesis.<ref name="Penrose1994"/>

The Penrose–Lucas argument was criticized by mathematicians,<ref name=laforte_1998>LaForte, Geoffrey, Patrick J. Hayes, and Kenneth M. Ford 1998.''[https://web.archive.org/web/20060901233518/http://www.cs.uwf.edu/~glaforte/papers/whyGodel.ps Why Gödel's Theorem Cannot Refute Computationalism]''. Artificial Intelligence, 104:265–286.</ref><ref name=solomon_1996>{{cite journal | author-link = Solomon Feferman | last = Feferman | first = Solomon | year = 1996 |citeseerx = 10.1.1.130.7027 | title = Penrose's Gödelian argument | journal = [[Psyche (consciousness journal)|Psyche]] | volume = 2 | pages = 21–32 }}</ref><ref name=krajewski_2007>{{cite journal |last1=Krajewski |first1=Stanisław |title=On Gödel's Theorem and Mechanism: Inconsistency or Unsoundness is Unavoidable in any Attempt to 'Out-Gö del' the Mechanist |journal=Fundamenta Informaticae |date=2007 |volume=81 |issue=1–3 |pages=173–181 |url=https://content.iospress.com/articles/fundamenta-informaticae/fi81-1-3-11 }}</ref> computer scientists,<ref name=putnam_1995/> and philosophers,<ref name=mindpapers>{{cite web|url=http://consc.net/mindpapers/6.1b |title=MindPapers: 6.1b. Godelian arguments |publisher=Consc.net |access-date=2014-07-28}}</ref><ref name=lucas_criticisms>{{cite web|url=http://users.ox.ac.uk/~jrlucas/Godel/referenc.html |title=References for Criticisms of the Gödelian Argument |publisher=Users.ox.ac.uk |date=1999-07-10 |access-date=2014-07-28}}</ref><ref name=Boolos_1990/><ref name=martin_1993/><ref name=lewis_1969/> and the consensus among experts in these fields is that the argument fails,<ref>{{cite journal |last1=Bringsjord |first1=Selmer |last2=Xiao |first2=Hong |title=A refutation of Penrose's Gödelian case against artificial intelligence |journal=Journal of Experimental & Theoretical Artificial Intelligence |date=July 2000 |volume=12 |issue=3 |pages=307–329 |doi=10.1080/09528130050111455 |s2cid=5540500 |url=http://cogprints.org/553/3/pen.sel8.pdf }}</ref><ref>In an article at {{cite web |url=http://www.mth.kcl.ac.uk/~llandau/Homepage/Math/penrose.html |title=King's College London - Department of Mathematics |access-date=2010-10-22 |url-status=dead |archive-url=https://web.archive.org/web/20010125011300/http://www.mth.kcl.ac.uk/~llandau/Homepage/Math/penrose.html |archive-date=2001-01-25 }} L.J. Landau at the Mathematics Department of King's College London writes that "Penrose's argument, its basis and implications, is rejected by experts in the fields which it touches."</ref><ref name="Burgess">Princeton Philosophy professor John Burgess writes in ''[http://www.princeton.edu/~jburgess/Montreal.doc On the Outside Looking In: A Caution about Conservativeness]'' (published in Kurt Gödel: Essays for his Centennial, with the following comments found on [https://books.google.com/books?id=83Attf6BsJ4C&pg=PA131 pp. 131–132]) that "the consensus view of logicians today seems to be that the Lucas–Penrose argument is fallacious, though as I have said elsewhere, there is at least this much to be said for Lucas and Penrose, that logicians are not unanimously agreed as to where precisely the fallacy in their argument lies. There are at least three points at which the argument may be attacked."</ref> with different authors attacking different aspects of the argument.<ref name="Burgess" /><ref>[[Nachum Dershowitz|Dershowitz, Nachum]] 2005. ''[http://www.cs.tau.ac.il/~nachumd/papers/FourSonsOfPenrose.pdf The Four Sons of Penrose]'', in ''Proceedings of the Eleventh Conference on [[Logic for Programming, Artificial Intelligence, and Reasoning]] (LPAR; Jamaica)'', G. Sutcliffe and A. Voronkov, eds., Lecture Notes in Computer Science, vol. 3835, Springer-Verlag, Berlin, pp. 125–138.</ref> [[Marvin Minsky|Minsky]] argued that because humans can believe false ideas to be true, human mathematical understanding need not be consistent and consciousness may easily have a deterministic basis.<ref>Marvin Minsky. "Conscious Machines." Machinery of Consciousness, Proceedings, National Research Council of Canada, 75th Anniversary Symposium on Science in Society, June 1991.</ref> [[Solomon Feferman|Feferman]] argued that mathematicians do not progress by mechanistic search through proofs, but by trial-and-error reasoning, insight and inspiration, and that machines do not share this approach with humans.<ref name=solomon_1996/>

==Orch OR==
Penrose outlined a predecessor to Orch OR in ''The Emperor's New Mind'', coming to the problem from a mathematical viewpoint and in particular Gödel's theorem, but lacked a detailed proposal for how quantum processes could be implemented in the brain. [[Stuart Hameroff]] separately worked in cancer research and [[anesthesia]], which gave him an interest in brain processes. Hameroff read Penrose's book and suggested to him that [[microtubule]]s within neurons were suitable candidate sites for quantum processing, and ultimately for consciousness.<ref name="Hameroff1982">{{cite journal |last1=Hameroff |first1=Stuart R. |last2=Watt |first2=Richard C. |title=Information processing in microtubules |journal=Journal of Theoretical Biology |date=October 1982 |volume=98 |issue=4 |pages=549–561 |doi=10.1016/0022-5193(82)90137-0 |pmid=6185798 |bibcode=1982JThBi..98..549H }}</ref><ref name="Hameroff1987">{{cite book |author=Hameroff, S.R. |title=Ultimate Computing |publisher=[[Elsevier]] |year=1987 |url=https://archive.org/details/ultimatecomputin00hame |isbn=978-0-444-70283-8 }}</ref> Throughout the 1990s, the two collaborated on the Orch OR theory, which Penrose published in ''[[Shadows of the Mind]]'' (1994).<ref name=Penrose1994/>

Hameroff's contribution to the theory derived from his study of the neural [[cytoskeleton]], and particularly on microtubules.<ref name=Hameroff1987/> As neuroscience has progressed, the role of the cytoskeleton and microtubules has assumed greater importance. In addition to providing structural support, microtubule functions include [[axoplasmic transport]] and control of the cell's movement, growth and shape.<ref name=Hameroff1987/>

Orch OR combines the Penrose–Lucas argument with Hameroff's hypothesis on quantum processing in microtubules. It proposes that when condensates in the brain undergo an objective wave function reduction, their collapse connects noncomputational decision-making to experiences embedded in spacetime's fundamental geometry. The theory further proposes that the microtubules both influence and are influenced by the conventional activity at the synapses between neurons.

===Microtubule computation===
[[File:Microtubule diagram.jpg|thumb|300px|<small>'''A:'''</small> An [[axon terminal]] releases [[neurotransmitter]]s through a synapse and are received by microtubules in a neuron's [[dendritic spine]].<br><small>'''B:'''</small> Simulated microtubule tubulins switch states.<ref name=frontiers/>]]
Hameroff proposed that microtubules were suitable candidates for quantum processing.<ref name=Hameroff1987/> Microtubules are made up of [[tubulin]] [[protein]] subunits. The tubulin protein [[Dimer (biochemistry)|dimers]] of the microtubules have [[hydrophobic]] pockets that may contain delocalized [[π electron]]s. Tubulin has other, smaller non-polar regions, for example 8 [[tryptophan]]s per tubulin, which contain π electron-rich [[indole]] rings distributed throughout tubulin with separations of roughly 2&nbsp;nm. Hameroff claims that this is close enough for the tubulin π electrons to become [[quantum entanglement|quantum entangled]].<ref name=Hameroff_2007>{{cite book |last=Hameroff |first=Stuart |author-link=Stuart Hameroff |chapter=That's life! The geometry of π electron resonance clouds |title=Quantum aspects of life |editor-last=Abbott |editor1-first=D |editor2-last=Davies |editor2-first=P |editor3-last=Pati |editor3-first=A |chapter-url=http://www.quantumconsciousness.org/documents/Hameroff_received-1-05-07.pdf |year=2008 |publisher=World Scientific |pages=403–434 |access-date=Jan 21, 2010 |archive-date=June 11, 2011 |archive-url=https://web.archive.org/web/20110611163201/http://www.quantumconsciousness.org/documents/Hameroff_received-1-05-07.pdf |url-status=dead }}</ref> During entanglement, particle states become inseparably correlated.

Hameroff originally suggested in the fringe ''[[Journal of Cosmology]]'' that the tubulin-subunit electrons would form a [[Bose–Einstein condensate]].<ref name="Penrose-Hameroff2011">{{cite journal 
|author1=Roger Penrose  |author2=Stuart Hameroff  |name-list-style=amp |title= Consciousness in the Universe: Neuroscience, Quantum Space-Time Geometry and Orch OR Theory |journal= Journal of Cosmology |volume= 14 |year= 2011 |url= http://journalofcosmology.com/Consciousness160.html|archive-url= https://web.archive.org/web/20140207124412/http://journalofcosmology.com/Consciousness160.html|url-status= dead|archive-date= February 7, 2014}}</ref> He then proposed a [[Frohlich condensate]], a hypothetical coherent oscillation of dipolar molecules. However, this too was rejected by Reimers's group.<ref name="Reimers2009">{{cite journal |doi=10.1073/pnas.0806273106 |pmid=19251667 |pmc=2657444 |title=Weak, strong, and coherent regimes of Frohlich condensation and their applications to terahertz medicine and quantum consciousness |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=11 |pages=4219–4224 |year=2009 |last1=Reimers |first1=J. R. |last2=McKemmish |first2=L. K. |last3=McKenzie |first3=R. H. |last4=Mark |first4=A. E. |last5=Hush |first5=N. S. |bibcode=2009PNAS..106.4219R |doi-access=free }}</ref> Hameroff and Penrose contested the conclusion, considering that Reimers's microtubule model was oversimplified.<ref>{{Cite journal |last1=Hameroff |first1=Stuart |last2=Penrose |first2=Roger |date=2014-03-01 |title=Consciousness in the universe: A review of the 'Orch OR' theory |journal=Physics of Life Reviews |volume=11 |issue=1 |pages=39–78 |doi=10.1016/j.plrev.2013.08.002 |issn=1571-0645|doi-access=free |pmid=24070914 |bibcode=2014PhLRv..11...39H }}</ref>

Hameroff then proposed that condensates in microtubules in one [[neuron]] can link with microtubule condensates in other neurons and [[glial cell]]s via the [[gap junctions]] of [[electrical synapse]]s.<ref name="Hameroff2006a">{{cite journal |doi=10.1097/00000542-200608000-00024 |author=Hameroff, S.R. |title=The entwined mysteries of anesthesia and consciousness |journal=Anesthesiology |volume=105 |issue=2 |pages=400–412 |year=2006 |pmid=16871075|s2cid=1655684 |doi-access=free }}</ref><ref name="Hameroff2009">{{cite journal |author= Hameroff, S. |title=The "conscious pilot"—dendritic synchrony moves through the brain to mediate consciousness |journal=Journal of Biological Physics |volume= 36 |pages= 71–93 |year=2009 |doi=10.1007/s10867-009-9148-x |pmid= 19669425 |issue= 1 |pmc= 2791805}}</ref> Hameroff proposed that the gap between the cells is sufficiently small that quantum objects can [[quantum tunneling|tunnel]] across it, allowing them to extend across a large area of the brain. He further postulated that the action of this large-scale quantum activity is the source of 40&nbsp;Hz [[gamma wave]]s, building upon the much less controversial theory that gap junctions are related to the gamma oscillation.<ref name="Bennett&Zukin2004">{{cite journal |author1=Bennett, M.V.L. |author2=Zukin, R.S.  |name-list-style=amp |title=Electrical Coupling and Neuronal Synchronization in the Mammalian Brain |journal=Neuron |volume=41 |issue=4 |pages=495–511 |year=2004 |pmid=14980200 |doi=10.1016/S0896-6273(04)00043-1|s2cid=18566176 |doi-access=free }}</ref>

===Related experimental results===

==== Superradiance ====
In a study Hameroff was part of, [[Jack Tuszyński]] of the [[University of Alberta]] demonstrated that anesthetics hasten the duration of a process called delayed luminescence, in which microtubules and tubulins {{Nowrap|re-emit}} trapped light. Tuszyński suspects that the phenomenon has a quantum origin, with [[superradiance]] being investigated as one possibility (in a 2024 study, superradiance was confirmed to occur in networks of [[tryptophan]]s, which are found in microtubules).<ref name=":0">{{cite web |date=April 29, 2024 |title=Ultraviolet superradiance from mega-networks of tryptophan in biological architectures |url=https://www.eurekalert.org/news-releases/1042789 |access-date=2024-10-03 |website=[[EurekAlert]]}}</ref><ref name=":1">{{Cite journal |last1=Babcock |first1=N. S. |last2=Montes-Cabrera |first2=G. |last3=Oberhofer |first3=K. E. |last4=Chergui |first4=M. |last5=Celardo |first5=G. L. |last6=Kurian |first6=P. |date=2024 |title=Ultraviolet Superradiance from Mega-Networks of Tryptophan in Biological Architectures |journal=The Journal of Physical Chemistry B |volume=128 |issue=17 |pages=4035–4046 |doi=10.1021/acs.jpcb.3c07936 |pmc=11075083 |pmid=38641327}}</ref> Tuszyński told ''New Scientist'' that "We're not at the level of interpreting this physiologically, saying 'Yeah, this is where consciousness begins,' but it may."<ref>{{cite web |last1=Tangermann |first1=Victor |date=19 April 2022 |title=Experiment Suggests That Consciousness May Be Rooted in Quantum Physics |url=https://futurism.com/human-consciousness-quantum-physics |access-date=24 April 2022 |website=Futurism |publisher=Camden Media Inc}}</ref>

The 2024 study, called Ultraviolet Superradiance from Mega-Networks of Tryptophan in Biological Architectures and published in ''[[The Journal of Physical Chemistry]]'', confirmed superradiance in networks of tryptophans.<ref name=":0" /><ref name=":1" /> Large networks of tryptophans are a warm and noisy environment, in which quantum effects typically are not expected to take place.<ref name=":0" /> The results of the study were theoretically predicted and then experimentally confirmed by the researchers.<ref name=":0" /><ref name=":1" /> [[Majed Chergui]], who led the experimental team, stated that "It's a beautiful result. It took very precise and careful application of standard protein spectroscopy methods, but guided by the theoretical predictions of our collaborators, we were able to confirm a stunning signature of superradiance in a micron-scale biological system."<ref name=":0" /> [[Marlan Scully]], a physicist well-known for his work in the field of theoretical quantum optics, said "We will certainly be examining closely the implications for quantum effects in living systems for years to come."<ref name=":0" /> The study states that "by analyzing the coupling with the electromagnetic field of mega-networks of tryptophans present in these biologically relevant architectures, we find the emergence of collective quantum optical effects, namely, superradiant and subradiant eigenmodes.&nbsp;... our work demonstrates that collective and cooperative UV excitations in mega-networks of tryptophans support robust quantum states in protein aggregates, with observed consequences even under thermal equilibrium conditions."<ref name=":1" />

==== Microtubule quantum vibration theory of anesthetic action ====
In an experiment, [[Gregory D. Scholes]] and Aarat Kalra of [[Princeton University]] used lasers to excite molecules within tubulins, causing a prolonged excitation to diffuse through microtubules farther than expected, which did not occur when repeated under anesthesia.<ref>{{cite web |last1=Lewton |first1=Thomas |date=18 April 2022 |title=Quantum experiments add weight to a fringe theory of consciousness |url=https://www.newscientist.com/article/2316408-quantum-experiments-add-weight-to-a-fringe-theory-of-consciousness/ |url-access=subscription |access-date=23 April 2022 |website=[[New Scientist]]}}</ref> However, diffusion results have to be interpreted carefully, since even classical diffusion can be very complex due to the wide range of length scales in the fluid filled extracellular space.<ref>{{cite journal |last1=Nicholson |first1=Charles |date=May 2022 |title=The Secret World in the Gaps between Brain Cells |journal=Physics Today |volume=75 |issue=5 |pages=26–32 |bibcode=2022PhT....75e..26N |doi=10.1063/PT.3.4999 |s2cid=248620292}}</ref>

At high concentrations (~5 [[Minimum alveolar concentration|MAC]]) the anesthetic gas [[halothane]] causes reversible depolymerization of microtubules.<ref>{{Cite journal|last1=Allison|first1=A.C|last2=Nunn|first2=J.F|date=December 1968|journal=The Lancet|volume=292|issue=7582|pages=1326–1329|doi=10.1016/s0140-6736(68)91821-7|pmid=4177393|issn=0140-6736|title=Effects of General Anæsthetics on Microtubules}}</ref> This cannot be the mechanism of anesthetic action, however, because human anesthesia is performed at 1 [[minimum alveolar concentration|MAC]]. (Neither Penrose or Hameroff claim that depolymerization is the mechanism of action for Orch OR.)<ref>{{cite journal | doi=10.1016/j.plrev.2013.08.002 | title=Consciousness in the universe | year=2014 | last1=Hameroff | first1=Stuart | last2=Penrose | first2=Roger | journal=Physics of Life Reviews | volume=11 | issue=1 | pages=39–78 | pmid=24070914 | bibcode=2014PhLRv..11...39H | s2cid=5015743 | doi-access=free }}</ref><ref>{{Cite web |last1=Hameroff |first1=Stuart |last2=Penrose |first2=Roger |date=1996 |title=Orchestrated Objective Reduction of Quantum Coherence in Brain Microtubules: The "Orch OR" Model for Consciousness |url=https://bigbangpage.com/wp-content/uploads/2015/04/orchestrated-objective-reduction-in-microtubuls...pdf |website=bigbangpage.com}}</ref> At ~1 MAC halothane, reported minor changes in tubulin protein expression (~1.3-fold) in primary cortical neurons after exposure to halothane and isoflurane are not evidence that tubulin directly interacts with general anesthetics, but rather shows that the proteins controlling tubulin production are possible anesthetic targets.<ref>{{Cite journal|last1=Pan|first1=Jonathan Z.|last2=Xi|first2=Jin|last3=Eckenhoff|first3=Maryellen F.|last4=Eckenhoff|first4=Roderic G.|date=July 2008|title=Inhaled anesthetics elicit region-specific changes in protein expression in mammalian brain|journal=Proteomics|volume=8|issue=14|pages=2983–2992|doi=10.1002/pmic.200800057|pmid=18655074|s2cid=24559322|issn=1615-9853|doi-access=free}}</ref> Further proteomic study reports 0.5 mM [<sup>14</sup>C]halothane binding to tubulin monomers alongside three dozens of other proteins.<ref name="Pan2007">{{cite journal
 | last1 = Pan
 | first1 = Jonathan Z.
 | last2 = Xi
 | first2 = Jin
 | last3 = Tobias
 | first3 = John W.
 | last4 = Eckenhoff
 | first4 = Maryellen F.
 | last5 = Eckenhoff
 | first5 = Roderic G.
 | title = Halothane binding proteome in human brain cortex
 | journal = Journal of Proteome Research
 | volume = 6
 | number = 2
 | pages = 582–592
 | doi = 10.1021/pr060311u
 | year = 2007
| pmid = 17269715
 }}</ref> In addition, modulation of microtubule stability has been reported during anthracene general anesthesia of tadpoles.<ref name=":3">{{Cite journal|last1=Emerson|first1=Daniel J.|last2=Weiser|first2=Brian P.|last3=Psonis|first3=John|last4=Liao|first4=Zhengzheng|last5=Taratula|first5=Olena|last6=Fiamengo|first6=Ashley|last7=Wang|first7=Xiaozhao|last8=Sugasawa|first8=Keizo|last9=Smith|first9=Amos B.|date=2013-03-29|title=Direct Modulation of Microtubule Stability Contributes to Anthracene General Anesthesia|journal=Journal of the American Chemical Society|volume=135|issue=14|pages=5389–5398|doi=10.1021/ja311171u|pmid=23484901|issn=0002-7863|pmc=3671381|bibcode=2013JAChS.135.5389E }}</ref> The study called Direct Modulation of Microtubule Stability Contributes to Anthracene General Anesthesia claims to provide "strong evidence that destabilization of neuronal microtubules provides a path to achieving general anesthesia".<ref name=":3" />

A highly disputed theory put forth in the mid-1990s by Hameroff and Penrose posits that consciousness is based on quantum vibrations in tubulin/microtubules inside brain neurons. Computer modeling of tubulin's atomic structure<ref>{{Cite journal|last1=Craddock|first1=Travis J. A.|last2=St. George|first2=Marc|last3=Freedman|first3=Holly|last4=Barakat|first4=Khaled H.|last5=Damaraju|first5=Sambasivarao|last6=Hameroff|first6=Stuart|last7=Tuszynski|first7=Jack A.|date=2012-06-25|title=Computational Predictions of Volatile Anesthetic Interactions with the Microtubule Cytoskeleton: Implications for Side Effects of General Anesthesia|journal=PLOS ONE|volume=7|issue=6|pages=e37251|doi=10.1371/journal.pone.0037251|pmid=22761654|pmc=3382613|issn=1932-6203|bibcode=2012PLoSO...737251C|doi-access=free}}</ref> found that anesthetic gas molecules bind adjacent to amino acid aromatic rings of non-polar [[pi electron|π-electrons]] and that collective quantum dipole oscillations among all π-electron resonance rings in each tubulin showed a spectrum with a common mode peak at 613 [[Tera-|T]][[Hz]].<ref name="Craddock2017">{{Cite journal|last1=Craddock|first1=Travis J. A.|last2=Kurian|first2=Philip|last3=Preto|first3=Jordane|last4=Sahu|first4=Kamlesh|last5=Hameroff|first5=Stuart R.|last6=Klobukowski|first6=Mariusz|last7=Tuszynski|first7=Jack A.|date=2017-08-29|title=Anesthetic Alterations of Collective Terahertz Oscillations in Tubulin Correlate with Clinical Potency: Implications for Anesthetic Action and Post-Operative Cognitive Dysfunction|journal=Scientific Reports|volume=7|issue=1|pages=9877|doi=10.1038/s41598-017-09992-7|pmid=28852014|pmc=5575257|issn=2045-2322|bibcode=2017NatSR...7.9877C}}</ref> Simulated presence of 8 different anesthetic gases abolished the 613 THz peak, whereas the presence of 2 different nonanesthetic gases did not affect the 613 THz peak, from which it was speculated that this 613 THz peak in microtubules could be related to consciousness and anesthetic action.<ref name="Craddock2017" />

Another study that Hameroff was a part of claims to show "anesthetic molecules can impair π-resonance energy transfer and exciton hopping in 'quantum channels' of tryptophan rings in tubulin, and thus account for selective action of anesthetics on consciousness and memory".<ref>{{Cite journal |title=Anesthetics act in quantum channels in brain microtubules to prevent consciousness |url=https://pubmed.ncbi.nlm.nih.gov/25714379/ |journal=Current Topics in Medicinal Chemistry|date=2015 |pmid=25714379 |last1=Craddock |first1=T. J. |last2=Hameroff |first2=S. R. |last3=Ayoub |first3=A. T. |last4=Klobukowski |first4=M. |last5=Tuszynski |first5=J. A. |volume=15 |issue=6 |pages=523–533 |doi=10.2174/1568026615666150225104543 }}</ref>

In a study published in August 2024, an undergraduate group led by a [[Wellesley College]] professor found that rats given [[Epothilone|epothilone&nbsp;B]], a drug that binds to microtubules, took over a minute longer to fall unconscious when exposed to an anesthetic gas.<ref>{{Cite web |date=2024-09-06 |title=Study Supports Quantum Basis of Consciousness in the Brain |url=https://neurosciencenews.com/quantum-process-consciousness-27624/ |access-date=2024-10-04 |website=Neuroscience News |language=en-US}}</ref>

==Criticism==
Orch OR has been criticized both by physicists<ref name="Tegmark2000" /><ref name="McKemmish2009">{{cite journal |last1=McKemmish |first1=Laura K. |last2=Reimers |first2=Jeffrey R. |last3=McKenzie |first3=Ross H. |last4=Mark |first4=Alan E. |last5=Hush |first5=Noel S. |title=Penrose-Hameroff orchestrated objective-reduction proposal for human consciousness is not biologically feasible |journal=Physical Review E |date=13 August 2009 |volume=80 |issue=2 |pages=021912 |doi=10.1103/PhysRevE.80.021912 |pmid=19792156 |bibcode=2009PhRvE..80b1912M |url=https://espace.library.uq.edu.au/view/UQ:200232/UQ200232.pdf }}</ref><ref name="Reimers2009" /><ref name="Reimers2013">{{cite journal|last1=Reimers|first1=Jeffrey R.|last2=McKemmish|first2=Laura K.|last3=McKenzie|first3=Ross H.|last4=Mark|first4=Alan E.|last5=Hush|first5=Noel S.|year=2014|title=The revised Penrose–Hameroff orchestrated objective-reduction proposal for human consciousness is not scientifically justified|journal=Physics of Life Reviews|volume=11|issue=1|pages=101–103|bibcode=2014PhLRv..11..101R|doi=10.1016/j.plrev.2013.11.003|pmid=24268490}}</ref><ref name="Villatoro2015">{{cite web |url = https://mappingignorance.org/2015/06/17/on-the-quantum-theory-of-consciousness/ |title = On the quantum theory of consciousness |last = Villatoro |first = Francisco R. |date = June 17, 2015 |website = Mapping Ignorance |publisher = University of the Basque Country |access-date = August 18, 2018 |quote= Hameroff's ideas in the hands of Penrose have developed almost to absurdity.}}</ref> and [[neuroscientist]]s<ref name="Baars2012">{{cite journal |vauthors=Baars BJ, Edelman DB | title = Consciousness, biology and quantum hypotheses | journal = Physics of Life Reviews | volume = 9 | issue = 3 | pages = 285–294 | year = 2012 | doi = 10.1016/j.plrev.2012.07.001 | pmid = 22925839| bibcode = 2012PhLRv...9..285B }}</ref><ref name="Georgiev2017">{{cite book | last = Georgiev | first = Danko D. | title = Quantum Information and Consciousness: A Gentle Introduction | publisher = CRC Press | year = 2017 | location = Boca Raton | isbn =  9781138104488 | oclc = 1003273264 | page=177|url=https://books.google.com/books?id=OtRBDwAAQBAJ&pg=PT177}}</ref><ref name="Litt2006">{{cite journal |vauthors=Litt A, Eliasmith C, Kroon FW, Weinstein S, Thagard P | title = Is the brain a quantum computer? | journal = Cognitive Science | volume = 30 | issue = 3 | pages = 593–603 | year = 2006 | doi = 10.1207/s15516709cog0000_59 | pmid = 21702826
| doi-access = free }}</ref> who consider it to be a poor model of brain [[physiology]]. Orch OR has also been criticized for lacking [[explanatory power]]; the philosopher [[Patricia Churchland]] wrote, "Pixie dust in the synapses is about as explanatorily powerful as quantum coherence in the microtubules."<ref>{{cite web|url=https://patriciachurchland.com/wp-content/uploads/2020/07/1997-Brainshy-NonNeural-Theories-of-Conscious-Experience.pdf |title=Brainshy: Non-Neural Theories of Conscious Experience |access-date=2021-03-03 |first=Patricia S. |last=Churchland}}</ref>

[[David Chalmers]] argues against quantum consciousness. He instead discusses how quantum mechanics may relate to [[Mind–body dualism|dualistic consciousness]].<ref name="Chalmers2003">{{cite book |author1=Stephen P. Stich |url=https://books.google.com/books?id=NEGK_ZStddkC&q=dualistic+consciousness&pg=PA126 |title=The Blackwell Guide to Philosophy of Mind |author2=Ted A. Warfield |date=15 April 2008 |publisher=John Wiley & Sons |isbn=9780470998755 |page=126}}</ref> Chalmers is skeptical that any new physics can resolve the [[hard problem of consciousness]].<ref name="Chalmers1995">{{cite journal |author =  David J. Chalmers|author-link=David Chalmers|title = Facing Up to the Problem of Consciousness |journal = Journal of Consciousness Studies|volume = 2 |issue = 3 |year = 1995 |pages = 200–219 |url = http://consc.net/papers/facing.html}}</ref><ref name="Chalmers1997">{{cite book |last1=Chalmers |first1=David J. |title=The Conscious Mind: In Search of a Fundamental Theory |date=1997 |publisher=Oxford University Press |location=New York |isbn=978-0-19-511789-9 |edition=Paperback}}</ref><ref name="David Chalmers 1996">{{cite book |author=David Chalmers |title=The Conscious Mind: In Search of a Fundamental Theory |isbn=978-0-19-510553-7 |url-access=registration |url=https://archive.org/details/consciousmindins00chal |publisher=Oxford University Press |year=1996 }}</ref> He argues that quantum theories of consciousness suffer from the same weakness as more conventional theories. Just as he argues that there is no particular reason why particular macroscopic physical features in the brain should give rise to consciousness, he also thinks that there is no particular reason why a particular quantum feature, such as the EM field in the brain, should give rise to consciousness either.<ref name="David Chalmers 1996"/>

===Decoherence in living organisms===
In 2000 [[Max Tegmark]] claimed that any quantum coherent system in the brain would undergo effective [[wave function collapse]] due to environmental interaction long before it could influence neural processes (the "warm, wet and noisy" argument, as it later came to be known).<ref name=Tegmark2000/> He determined the decoherence timescale of microtubule entanglement at brain temperatures to be on the order of [[femtosecond]]s, far too brief for neural processing. [[Christof Koch]] and [[Klaus Hepp]] also agreed that [[Coherence (physics)#Quantum coherence|quantum coherence]] does not play, or does not need to play any major role in [[neurophysiology]].<ref name=Koch2006/><ref name=Hepp2012/> Koch and Hepp concluded that "The empirical demonstration of slowly decoherent and controllable quantum bits in neurons connected by electrical or chemical synapses, or the discovery of an efficient quantum algorithm for computations performed by the brain, would do much to bring these speculations from the 'far-out' to the mere 'very unlikely'."<ref name=Koch2006/>

In response to Tegmark's claims, Hagan, Tuszynski and Hameroff claimed that Tegmark did not address the Orch OR model, but instead a model of his own construction. This involved superpositions of quanta separated by 24&nbsp;nm rather than the much smaller separations stipulated for Orch OR. As a result, Hameroff's group claimed a decoherence time seven orders of magnitude greater than Tegmark's, although still far below 25&nbsp;ms. Hameroff's group also suggested that the [[Debye force|Debye]] layer of [[counterion]]s could screen thermal fluctuations, and that the surrounding [[actin]] [[gel]] might enhance the ordering of water, further screening noise. They also suggested that incoherent metabolic energy could further order water, and finally that the configuration of the microtubule lattice might be suitable for [[quantum error correction]], a means of resisting quantum decoherence.<ref name="Hagan2002">{{cite journal|last1=Hagan|first1=S.|last2=Hameroff|first2=S. R.|last3=Tuszyński|first3=J. A.|year=2002|title=Quantum computation in brain microtubules: Decoherence and biological feasibility|journal=Physical Review E|volume=65|issue=6|pages=061901|arxiv=quant-ph/0005025|bibcode=2002PhRvE..65f1901H|doi=10.1103/PhysRevE.65.061901|pmid=12188753|s2cid=11707566}}</ref><ref name="Hameroff2006b">{{cite book |doi=10.1007/3-540-36723-3 |title=The Emerging Physics of Consciousness |series=The Frontiers Collection |year=2006 |bibcode=2006epc..book.....T |isbn=978-3-540-23890-4 |url=https://cds.cern.ch/record/1338905 |editor-last1=Tuszynski |editor-first1=Jack A |pages=193–253 }}</ref>

In 2009, Reimers ''et al.'' and McKemmish ''et al.,'' published critical assessments. Earlier versions of the theory had required tubulin-electrons to form either [[Bose–Einstein condensate|Bose–Einstein]]s or [[Herbert Fröhlich|Frohlich]] condensates, and the Reimers group noted the lack of empirical evidence that such could occur. Additionally they calculated that microtubules could only support weak 8&nbsp;MHz coherence. McKemmish ''et al.'' argued that [[Aromaticity|aromatic molecules]] cannot switch states because they are delocalised; and that changes in tubulin protein-conformation driven by [[Guanosine triphosphate|GTP]] conversion would result in a prohibitive energy requirement.<ref name="McKemmish2009"/><ref name="Reimers2009"/><ref name="Reimers2013" />

In 2022, a group of Italian physicists conducted several experiments that failed to provide evidence in support of a gravity-related quantum collapse model of consciousness, weakening the possibility of a quantum explanation for consciousness.<ref>{{cite news|title=Collapsing a leading theory for the quantum origin of consciousness|url=https://phys.org/news/2022-06-collapsing-theory-quantum-consciousness.html|work=phys.org|date=13 June 2022}}</ref><ref>{{cite journal|last1=Derakhshani|first1=Maaneli|last2=Diósi|first2=Lajos|last3=Laubenstein|first3=Matthias|last4=Piscicchia|first4=Kristian|last5=Curceanu|first5=Catalina|title=At the crossroad of the search for spontaneous radiation and the Orch OR consciousness theory|journal=Physics of Life Reviews|date=1 September 2022|volume=42|pages=8–14|doi=10.1016/j.plrev.2022.05.004|pmid=35617922|bibcode=2022PhLRv..42....8D|s2cid=248868080}}</ref>

===Neuroscience===
{{further|Neuroscience}}
Biology-based criticisms have been offered, including a lack of explanation for the probabilistic release of [[neurotransmitter]] from presynaptic [[axon terminal]]s<ref name="Beck1992">{{cite journal |last1=Beck |first1=F |last2=Eccles |first2=J C |title=Quantum aspects of brain activity and the role of consciousness |journal=Proceedings of the National Academy of Sciences |date=December 1992 |volume=89 |issue=23 |pages=11357–11361 |doi=10.1073/pnas.89.23.11357 |pmid=1333607 |bibcode=1992PNAS...8911357B |pmc=50549 |doi-access=free }}</ref><ref name="Beck1996">{{cite journal |author=Beck |first=Friedrich |year=1996 |title=Can quantum processes control synaptic emission? |journal=International Journal of Neural Systems |volume=7 |issue=4 |pages=343–353 |bibcode=1995IJNS....6..145A |doi=10.1142/S0129065796000300 |pmid=8968823}}</ref><ref name="Beck1998">{{cite journal |last1=Beck |first1=Friedrich |last2=Eccles |first2=John C. |year=1998 |title=Quantum processes in the brain: A scientific basis of consciousness |journal=Cognitive Studies: Bulletin of the Japanese Cognitive Science Society |volume=5 |issue=2 |pages=95–109 |doi=10.11225/jcss.5.2_95}}</ref> and an error in the calculated number of the tubulin dimers per cortical neuron.<ref name="YuBaas1994">{{cite journal | pmc=6577472|  doi=10.1523/jneurosci.14-05-02818.1994 |title=Changes in microtubule number and length during axon differentiation |journal=The Journal of Neuroscience |volume=14 |issue=5 |pages=2818–2829 |year=1994 |last1=Yu |first1=W. |last2=Baas |first2=PW | pmid=8182441 |s2cid=11922397 |doi-access=free }}</ref>

In 2014, Penrose and Hameroff published responses to some criticisms and revisions to many of the theory's peripheral assumptions, while retaining the core hypothesis.<ref name="H&PvsReimers2014" /><ref name="HameroffVs7Others2014" />

==See also==
{{cols}}
* [[Copenhagen interpretation]]
* [[Electromagnetic theories of consciousness]]
* [[Holonomic brain theory]]
* [[Many-minds interpretation]]
* [[Penrose interpretation of Quantum Theory|Penrose interpretation]]
* [[Quantum Aspects of Life|''Quantum Aspects of Life'' (book)]]
* [[Quantum mind]]
* [[Quantum cognition]]
{{colend}}

==References==
{{reflist|2}}

==Sources==
* {{Citation | last=Hofstadter | first = Douglas | title = Gödel, Escher, Bach: an Eternal Golden Braid | year = 1979 | author-link = Douglas Hofstadter | title-link = Gödel, Escher, Bach }}
* {{Russell Norvig 2003}}
* {{Turing 1950}}

==External links==
* [http://consciousness.arizona.edu/ Center for Consciousness Studies]
* [http://www.quantumconsciousness.org/ Hameroff's "Quantum Consciousness" site]
* {{Cite web |last1=Hameroff |first1=Stuart |last2=Bandyopadhyay |first2=Anirban |last3=Lauretta |first3=Dante |author-link3=Dante Lauretta |date=2024-05-08 |title=Consciousness came before life |url=https://iai.tv/articles/life-and-consciousness-what-are-they-auid-2836 |website=[[Institute of Art and Ideas]] |language=en-GB}}
* [https://web.archive.org/web/20160514103339/http://online.kitp.ucsb.edu/plecture/penrose/ Penrose, Roger (1999). "Science and the Mind". Kavli Institute for Theoretical Physics Public Lectures.]

{{Roger Penrose}}
{{Consciousness}}

[[Category:Quantum mind]]
[[Category:Quantum biology]]
[[Category:Roger Penrose]]