Quantum mind–body problem
The quantum mind–body problem refers to the philosophical discussions of the mind–body problem in the context of quantum mechanics. Some interpretations of quantum mechanics posit a special role for consciousness in the process of quantum measurement.
- 1 Background and history
- 2 "Consciousness causes collapse"
- 3 Views of the pioneers of quantum mechanics
- 4 Quantum mysticism, New Age and New Thought belief
- 5 See also
- 6 Notes and references
- 7 External links
Background and history
In many philosophies[which?], the conscious mind is considered to be a separate entity, existing in a parallel realm not described by physical law. Some people[who?] claim that this idea gains support from the description of the physical world provided by quantum mechanics. Parallels between quantum mechanics and mind/body dualism were first drawn by the founders of quantum mechanics.
The reason is that quantum mechanics requires interpretation before it describes the experience of an observer. While particles and fields are described by a wavefunction, the results of observations are described by classical information which tells you the result. The information about observations is not in the wavefunction, but is additional random data. The wavefunction gives only the probability of getting different outcomes, and it turns into a classical probability only during the act of measurement, when its magnitude squared gives a probability for different outcomes.
The nature of observation has often been a point of contention in quantum mechanics, because quantum mechanics describes the experiences of observers with different numbers than it uses to describe material objects. With the notable exceptions of Louis DeBroglie, Max von Laue, Erwin Schrödinger and Albert Einstein, who believed that quantum mechanics was a statistical approximation to a deeper reality which is deterministic, most of the founders of quantum mechanics believed that this problem is purely philosophical. Eugene Wigner went further, and explicitly identified it as a quantum version of the mind-body problem.
Classical mind/body problem
In classical mechanics the world is measurable, the measurements reveal the true state of the world, and the behavior is deterministic. Given the initial positions and momentum of a collection of the basic particles, the future of those particles can be predicted. When these assumptions are applied to an observer the conclusion is that with enough information about the present, the entire future behavior of the observer will be determined. This led many scientists to reject pre-scientific notions of dualism, and to identify the mind of the observer with the classical state of the observer's atoms.
Yet even from a classical perspective many philosophers doubt that the material description of a hypothetical Newtonian observer is all that is necessary to understand internal experience. That is, they suggest that there may be a mind-body problem. Even though the atoms of the brain are constantly replaced, the information gets copied into new atoms, and perception continues into the new brain. In certain thought experiments, this type of copying leads to strange outcomes. For example, Daniel Dennett talks about the situation where a conscious Newtonian observer is duplicated, by having a second system store all the information in the brain. Once the second system is built, the two systems make two separate observers which contain the same information. The two observers start out exactly the same and receive the same sensory input, but eventually diverge. The divergence could be due to randomness, or glitches, or because the sensory input is slightly different; the reason is not important. The important thing is that one observer has been copied into two systems, and in such a situation it is not clear to this observer into which of the copies their experiences will continue.
Dennett notes this by assuming that he himself is copied. Before the copies diverge, there is no way for him to know which of the two copies he is. This bit of information becomes apparent to Dennett only after the two copies become different. He cannot know this information before the divergence, even if he is given full information about the material state of both copies.
Transition to quantum mechanics
The introduction of quantum mechanics substantially changed the status of the observer and measurements. The measurement problem studies how a classical observer can exist in a quantum world. The quantum world describes superpositions of very different states, but our perception is that of "classical" states in the macroscopic world, that is, a comparatively small subset of the states allowed by the quantum-mechanical superposition principle, having only a few, but determinate and robust, properties, such as position, momentum, etc. The question of why and how our experience of a "classical" world emerges from quantum mechanics thus lies at the heart of the foundational problems of quantum theory.
The determinism and materialism of classical mechanics divorced or at least distanced science from many pre-scientific philosophies that held various dualist perspectives towards the mind. Some scientists (like Wigner) believe that quantum mechanics makes certain dualist ideas about the mind/body problem acceptable again within mainstream science, while others think there is little to gain from science entertaining those possibilities further (as described in the criticism section below).
Observation in quantum mechanics
In the Copenhagen interpretation, quantum mechanics can only be used to predict the probabilities for different outcomes of pre-specified observations. What constitutes an "observer" or an "observation" is not directly specified by the theory, and the behavior of a system after observation is completely different than the usual behavior. During observation, the wavefunction describing the system collapses to one of several options. If there is no observation, this collapse does not occur, and none of the options ever become less likely.
Unlike classical mechanics, in quantum mechanics, there is no naive way of identifying the true state of the world. The wavefunction that describes a system spreads out into an ever larger superposition of different possible situations. Schrödinger's cat is an illustration of this: after interacting with a quantum system, the von Neumann/Wigner interpretation holds that the wavefunction of the cat describes it as a superposition of dead and alive. The standard interpretation, given by the Copenhagen interpretation is that the Geiger counter has already triggered the collapse of the wavefunction.
It can be predicted using quantum mechanics, absent a collapse postulate, that an observer observing a quantum superposition will turn into a superposition of different observers seeing different things. Just like Schrödinger's cat, the observer will have a wavefunction which describes all the possible outcomes. Still, in actual experience, an observer never feels a superposition, but always feels that one of the outcomes has occurred with certainty. This apparent conflict between a wavefunction description and classical experience is called the problem of observation (see: Measurement problem). The founders of quantum mechanics were aware of this problem, and had varying opinions about its resolution. These views reflect different stances on an argument which is anything but resolved today:
Albert Einstein, and with him Louis De Broglie and later David Bohm, believed that quantum mechanics was incomplete, that the wavefunction was only a statistical description of a deeper causal structure. Einstein saw quantum mechanics as analogous to statistical mechanics, and the wavefunction as just a peculiar statistical device for observers who are ignorant of the values of the hidden variables underneath. This point of view makes the extra information not at all mysterious – the results of observations are simply revealing the values of the hidden variables. David Bohm was able to explicitly formulate a nonlocal theory which reproduces the predictions of quantum mechanics. Although no error in Bohm's approach could be found, his theory did not find acceptance, and it was (incorrectly) believed that his theory was ruled out by an argument of John von Neumann. In 1964, John Bell realized that local hidden variables set a limit on the degree to which the results of distant experiments can be correlated, a limit which is violated in quantum mechanics. The experimental observation of violations of Bell's inequality showed that the original local hidden variables of Einstein, Podolsky, and Rosen could not be correct. Bell also criticized von Neumann's argument, showing that von Neumann's proof is not universally valid (i.e., applicable to all of the possible types of hidden variable theories), and does not rule out Bohm's theory. Most physicists do not accept hidden variable interpretations as compelling.
The mainstream of the scientific community adopted an approach attributed to Niels Bohr. Bohr believed that quantum mechanics was a complete description of nature, but that it was simply a language ill suited to describing the world of everyday experience, and that in the human realm experiences were described by classical mechanics and by probability. Later an amalgamated, Copenhagen interpretation, similar to the views of Max Born, Werner Heisenberg and others, became the standard view. It requires a demarcation line, a boundary, above which an object would cease to be quantum and would start to be classical. Bohr never specified this line precisely, since he believed that it was not a question of physics, but of pure philosophy or even convenience. Von Neumann, in his analysis of measurements, interpreted the demarcation line as the point where wave-function collapse occurs, and he showed that within quantum mechanics, the point of collapse is largely arbitrary, and may be placed anywhere from the first incoherent interaction with a complex enough object, to the interface of the brain with consciousness.
Decoherence and modern interpretations
Hugh Everett proposed an entirely mechanistic interpretation of quantum mechanics that has come to be known as the many-worlds interpretation. In Everett's view, the whole universe is a wavefunction (the universal wavefunction), describing a dizzying multiplicity of worlds. In this interpretation, observers are to be treated like computers, or as any other measuring device, as if their memories could be written out on magnetic tape. To understand the subjectively probabilistic nature of their experiences, one correlates the answer given by an observer with questions asked by a so-called external agency, who is likewise an observer and thus internal to the combined quantum system. Everett believed that this line of reasoning shows there is no conflict between the objective deterministic evolution of the wavefunction and the subjective indeterminate experiences of an observer.
Since the physical description in Everett's realist account is the deterministic wavefunction, the issue of interpretation is only relevant when analyzing the experience of an observer. The answer to the question "what does this observer see?" is only ambiguous to the extent that the specification of the observer is imprecise. An observer's state is a particular high dimensional projection of the universal wavefunction, but not all parts of the wavefunction describe a single observer – only those parts which describe a consistent past. In Everett's picture, the interpretation is a clarification, it tells you which observer you are examining.
A post-Everettian approach has been developed into a field of study called Quantum decoherence, which analyses the way in which classical behaviour emerges from quantum mechanics when the systems become large. Decoherence can be viewed as the loss of information from a system into the environment (often modeled as a heat bath), since every system is loosely coupled with the energetic state of its surroundings. Viewed in isolation, the system's dynamics are non-unitary (although the combined system plus environment evolves in a unitary fashion). Thus the dynamics of the system alone are irreversible. As with any coupling, entanglements are generated between the system and environment, which have the effect of sharing quantum information with – or transferring it to – the surroundings.
Decoherence does not generate literal wave function collapse. Rather, it only provides an explanation for the appearance of wavefunction collapse, as the quantum nature of the system "leaks" into the environment. That is, components of the wavefunction are decoupled from a coherent system, and acquire phases from their immediate surroundings. A total superposition of the universal wavefunction still exists (and remains coherent at the global level), but its fundamentality remains an interpretational issue. "Post-Everett" decoherence also answers the measurement problem, holding that literal wavefunction collapse simply doesn't exist. Rather, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".
According to E.J. Squires, the description of the observer in a decoherence approach, as in the Copenhagen approach, always involves extra information, the information which specifies the outcome of all the random events in the past. This information answers the question "which observer?" in many-worlds, and correspondingly answers the question "what outcomes of past measurements?" in the Copenhagen approach.
Squires associates this with the consciousness of the observer, because it is purportedly associated with the observer, not with the matter from which the observer is built. This includes most information about the universe.
The only form of interactionist dualism that has seemed even remotely tenable in the contemporary picture is one that exploits certain properties of quantum mechanics. There are two ways this might go. First, some [e.g., Eccles 1986] have appealed to the existence of quantum indeterminacy, and have suggested that a nonphysical consciousness might be responsible for filling the resultant causal gaps, determining which values some physical magnitudes might take within an apparently "probabilistic" distribution… Although these decisions would have only a tiny proximate effect, perhaps nonlinear dynamics could amplify these tiny fluctuations into significant macroscopic effects on behavior.
This is an audacious and interesting suggestion, but it has a number of problems… A second way in which quantum mechanics bears on the issue of causal closure lies with the fact that in some interpretations of the quantum formalism, consciousness itself plays a vital causal role, being required to bring about the so-called "collapse of the wave-function." This collapse is supposed to occur upon any act of measurement; and in one interpretation, the only way to distinguish a measurement from a nonmeasurement is via the presence of consciousness. This theory is certainly not universally accepted (for a start, it presupposes that consciousness is not itself physical, surely contrary to the views of most physicists), and I do not accept it myself, but in any case it seems that the kind of causal work consciousness performs here is quite different from the kind required for consciousness to play a role in directing behavior… In any case, all versions of interactionist dualism have a conceptual problem that suggests that they are less successful in avoiding epiphenomenalism than they might seem; or at least they are no better off than [naturalistic dualism]. Even on these views, there is a sense in which the phenomenal is irrelevant. We can always subtract the phenomenal component from any explanatory account, yielding a purely causal component.
— David Chalmers, The Conscious Mind: In Search of a Fundamental Theory, "The Irreducibility of Consciousness"
"Consciousness causes collapse"
In his 1932 book The Mathematical Foundations of Quantum Mechanics, John von Neumann argued that the mathematics of quantum mechanics allows for the collapse of the wave function to be placed at any position in the causal chain from the measurement device to the "subjective perception" of the human observer – the notion of such a chain, more specifically a chain of interacting systems in which the values of one system is correlated with that of the immediately following system, has since become known as the von Neumann chain. In 1939, F. London and E. Bauer argued for the latter boundary (consciousness). In the 1960s, Eugene Wigner reformulated the "Schrödinger's cat" thought experiment as "Wigner's friend" and proposed that the consciousness of an observer is the demarcation line which precipitates collapse of the wave function, independent of any realist interpretation. See Consciousness and measurement. Very technically, Wigner identified the non-linear probabilistic projection transformation which occurs during measurement with the selection of a definite state by a mind from the different possibilities which it could have in a quantum mechanical superposition. Thus, the non-physical mind is postulated to be the only true measurement apparatus. This interpretation has been summarized thus:
The rules of quantum mechanics are correct but there is only one system which may be treated with quantum mechanics, namely the entire material world. There exist external observers which cannot be treated within quantum mechanics, namely human (and perhaps animal) minds, which perform measurements on the brain causing wave function collapse.
Henry Stapp has argued for the concept as follows:
From the point of view of the mathematics of quantum theory it makes no sense to treat a measuring device as intrinsically different from the collection of atomic constituents that make it up. A device is just another part of the physical universe... Moreover, the conscious thoughts of a human observer ought to be causally connected most directly and immediately to what is happening in his brain, not to what is happening out at some measuring device... Our bodies and brains thus become...parts of the quantum mechanically described physical universe. Treating the entire physical universe in this unified way provides a conceptually simple and logically coherent theoretical foundation...
Hilary Putnam, a philosopher who has written on quantum mechanics a number of times, states that Consciousness Causes Collapse is no longer a popular view among physicists:-
[..]one might say --- von Neumann hints at this in his book, and Eugene Wigner famously advocated it -- "No, the collapse occurs when the result of a measurement is registered by a consciousness."
I do not know of anyone who currently advocates this "psychic" view, [..]
There are other possible solutions to the "Wigner's friend" thought experiment, which do not require consciousness to be different from other physical processes. Moreover, Wigner actually shifted to those interpretations (and away from "consciousness causes collapse") in his later years. This was partly because he was embarrassed that "consciousness causes collapse" can lead to a kind of solipsism, but also because he decided that he had been wrong to try to apply quantum physics at the scale of every day life (specifically, he rejected his initial idea of treating macroscopic objects as isolated systems—as one might microscopic objects). See, Consciousness and Superposition.
Recently, it has been argued that the results of delayed choice quantum eraser experiments effectively preclude the dualist or "consciousness" interpretation. Other researchers have expressed similar objections to the introduction of any subjective element in the collapse of the wavefunction.
To many scientists the dualist interpretation fails a priori to compete with other interpretations of quantum mechanics because "consciousness causes collapse" relies upon a dualistic philosophy of mind (in particular, a radical interactionism), which is inconsistent with the materialist monism presupposed by many physicists. The measurement problem not withstanding, they point to a causal closure of physics, suggesting a problem with how consciousness and matter might interact, reminiscent of objections to Descartes' substance dualism. Some physicists conclude that science's success at modeling the world materialistically—without reference to mental properties—vindicates that neglect. Psychology, on the other hand, has benefited from "an intellectual stampede" following Francis Crick and Christof Koch's challenge in 1990, that the time is ripe to tackle consciousness. Wigner accused materialist scientists of "exalting the problem [of the study of physical phenomena]". See also, Orch-OR.
Consciousness causes collapse theory does not explain which things have sufficient consciousness to collapse the wave function. A more fundamental issue is that it posits an important role for the conscious mind, and it has been questioned how this could be the case for the earlier universe, before consciousness had evolved or emerged. It has been argued that "[consciousness causes collapse] does not allow sensible discussion of Big Bang cosmology or biological evolution, at least on the assumption of an atheistic universe. For example, as Roger Penrose put it, "[T]he evolution of conscious life on this planet is due to appropriate mutations having taken place at various times. These, presumably, are quantum events, so they would exist only in linearly superposed form until they finally led to the evolution of a conscious being—whose very existence depends on all the right mutations having 'actually' taken place!"
Others further suppose a universal mind (see also pantheism and panentheism). To most physicists, including David Bohm and Basil Hiley, this merely pushes the problem back, which some see as a fatal unparsimonious move in a competition with other theories. Physicist Victor Stenger says that the "myth" of quantum consciousness has no scientific basis, nor does "the related belief that the human mind commands special powers—psychic forces—that transcend the material universe".
There are numerous philosophical interpretations of quantum mechanics competing with one another. Although measurement in quantum mechanics remains controversial, mainstream interpretations have never required a conscious observer to perform the wave function collapse, (by stipulation, a Geiger counter will do). Even less endearing to some is the many worlds interpretation, which spares no ontological expense to avoid it. In this interpretation, measurement results in a superposition, each outcome of an experiment persisting orthogonality (see Wigner's friend in Many Worlds). Decoherence alleviates the purported epistemic necessity of stipulating that wave function collapse occurs at some threshold of size, complexity, convenience or participation by providing a realist account without the superluminal and non-local requirements of objective collapse theories. Quantum effect rapidly decohere and become negligible during an interaction with the scientific instrument performing a measurement, absent any literal observer… Previously, scientists had not observed macroscopic quantum effects and assumed they never would.
Views of the pioneers of quantum mechanics
The originators of quantum mechanical theory held diverse opinions on this subject. Many of them held that humans can effectively interrogate nature through interacting with it, and that in this regard quantum mechanics is not different from classical mechanics. Werner Heisenberg maintained that wave function collapse—the destruction of quantum superposition—occurs when the result of a measurement is registered in the mind of an observer. Albert Einstein, who believed in determinism, and did not accept the theoretical completeness of quantum mechanics, considered the belief that consciousness has any effect on physics to be mystical and non-scientific.
Heisenberg and Bohr described quantum mechanics in logical positivist terms. Bohr also took an active interest in the philosophical implications of quantum theories such as his complementarity, for example. He believed quantum theory offers a complete description of nature, albeit one that is simply ill suited for everyday experiences—which are better described by classical mechanics and probability. Bohr never specified a demarcation line above which objects cease to be quantum and become classical. He believed that it was not a question of physics, but one of philosophy or convenience. 
Wolfgang Pauli interpreted the laws of quantum mechanics as leading to a lucid Platonic mysticism, a position intermediate between the skepticism of Western science centered on objective observer-independent facts, and the philosophies of ancient Eastern mysticism which put primary emphasis on conscious experience. Werner Heisenberg reported on Pauli's position, and his own, as follows:
...Pauli once spoke of two limiting conceptions, both of which have been extraordinarily fruitful in the history of human thought, although no genuine reality corresponds to them. At one extreme is the idea of an objective world, pursuing its regular course in space and time, independently of any kind of observing subject; this has been the guiding image of modern science. At the other extreme is the idea of a subject, mystically experiencing the unity of the world and no longer confronted by an object or by any objective world; this has been the guiding image of Asian mysticism. Our thinking moves somewhere in the middle, between these two limiting conceptions; we should maintain the tension resulting from these two opposites.
Quantum mysticism, New Age and New Thought belief
Fritjof Capra popularized the subject with The Tao of Physics. In this book, he notes that many of the founders of quantum mechanics believed that the theory meshes well with ancient Eastern mysticism and philosophy, including that of Hinduism, Taoism, and Buddhism which includes a belief in the transitory, interconnected nature of all things and the illusion of separation of thought and existence.
Deepak Chopra, a supporter of some of the ideas of consciousness causes collapse, appeals to the work of physicist Roger Penrose. Penrose pursued various lines of argument to suggest that human consciousness cannot be explained by existing principles in physics, but his arguments were rejected by experts in the relevant fields.
The view is also presented in various aspects of the New Thought Movement, the film What the Bleep Do We Know!?, and is a major plot point in Greg Egan's novel Quarantine and Dan Brown's novel The Lost Symbol.
- Association for the Scientific Study of Consciousness
- Free will
- Global Consciousness Project
- Heisenberg cut
- Interpretation of quantum mechanics
- Many-worlds interpretation
- Measurement in quantum mechanics
- Quantum indeterminacy
- Quantum mind
- Quantum Zeno effect
Notes and references
- This is an abbreviated paraphrase of the section entitled "The Language of Quantum Mechanics" in Wigner "Remarks on the Mind-Body Question"
- Roger Balian, in :Cini Levy-Leblond eds. "Quantum Theory without reduction" states (p.89): "Ever since the beginning of quantum mechanics, the measurement problem has been a subject of sometimes discontinued but nevertheless recurrent concern"
- pay link to Einstein letter Laue, Schrodinger and Einstein dissent
- Wigner, E. "Remarks on the Mind-Body Question", Symmetries and Reflections
- For example, Wigner states in "Remarks on the mind body question":"Until not many years ago, the existence of a mind or soul would have been passionately denied by most physical scientists. The brilliant successes of mechanistic and, more generally, macroscopic physics and of chemistry overshadowed the obvious fact that thoughts, desires, and emotions are not made of matter, and it was nearly universally accepted among physical scientists that there is nothing beside matter. The epistome of this belief was the conviction that, if we knew the positions and velocities of all atoms at one instant of time, we could compute the fate of the universe for all future"
- Haeckel, Ernst Heinrich Philip (1992). The Riddle of the Universe. Prometheus Books. ISBN 0-87975-746-9, 9780879757465 Check
- Kirk, Robert. 1974. "Sentience and Behaviour", Mind, vol. 83, pp. 43–60.
- Nagel, Thomas. 1970. "Armstrong on the Mind", Philosophical Review, vol. 79, pp. 394–403.
- Nagel, Thomas. 1974. "What is it Like to Be a Bat?" Philosophical Review, vol. 83, pp. 435–450.
- Dennett, Hofstadter, "The Mind's I" Basic Books
- Schreiber, Z. The Nine Lives of Schrödingers's Cat
- Amir D. Aczel, "entanglement"
- Although recently, the holographic principle of quantum gravity requires nonlocality for completely different reasons, which leads Gerard 't Hooft to propose that hidden variables should be revived. These hidden variables are different than Bohm's, since there would be too few of them to allow for quantum computation
- Niels Bohr (1928). "The Quantum Postulate and the Recent Development of Atomic Theory". Nature 121 (3050): 580–590. Bibcode:1928Natur.121..580B. doi:10.1038/121580a0. ": "[T]he quantum postulate implies that any observation of atomic phenomena will involve an interaction with the agency of observation not to be neglected. Accordingly, an independent reality in the ordinary physical sense can neither be ascribed to the phenomena nor to the agencies of observation. After all, the concept of observation is in so far arbitrary as it depends upon which objects are included in the system to be observed. Ultimately, every observation can, of course, be reduced to our sense perceptions. The circumstance, however, that in interpreting observations use has always to be made of theoretical notions entails that for every particular case it is a question of convenience at which point the concept of observation involving the quantum postulate with its inherent "irrationality" is brought in."
- Von Neumann, J., Mathematical Foundations of Quantum Mechanics, Princeton University Press, 1955.
- More precisely: "It will suffice for his purposes that observers possess memories, i.e. parts of a relatively permanent nature whose states are in correspondence with the past experience of the observer", quoting Bohm/Hiley: What this means is that, as in a computer whose memories are contained in the state of a disc, some aspects of the physical state of the observer, presumably within his brain, serves as the basis of his [or her] memories" Bohm & Hiley p.297
- De Witt, B. and Graham, M. "The Many Worlds interpretation of Quantum Mechanics", Princeton University Press
- Bohm/Hiley p.299
- Gell-Mann, M., "The Quark and the Jaguar", pp. 135-176
- Bacon, D. (2001). "Decoherence, control, and symmetry in quantum computers". arXiv:quant-ph/0305025.
- Lidar, Daniel A.; Whaley, K. Birgitta (2003). "Decoherence-Free Subspaces and Subsystems". In Benatti, F.; Floreanini, R. Irreversible Quantum Dynamics. Springer Lecture Notes in Physics 622. Berlin. pp. 83–120. arXiv:quant-ph/0301032.
- Wojciech H. Zurek, Decoherence, einselection, and the quantum origins of the classical,Reviews of Modern Physics 2003, 75, 715 or http://arxiv.org/abs/quant-ph/0105127
- E.J. Squires "An Attempt to Understand the Many-worlds Interpretation of Quantum Theory", collected in M. Cini, J.M- Levy-Leblond eds. , Quantum Theory without Reduction", ,1990, pp. 151-161
- Chalmers, David (1996). The Conscious Mind: In Search of a Fundamental Theory. Philosophy of Mind Series. Oxford University Press, USA. pp. 156–157. ISBN 978-0-19-983935-3.
- F. London and E. Bauer, "La théorie de l'observation en mécanique quantique" (1939), English translation in Quantum Theory and Measurement, edited by J.A. Wheeler and W.H. Zurek, Princeton University, Princeton, 1983, pp. 217–259.
- Stapp H, (2001). "Quantum Theory and the Role of Mind in Nature". Found. of Phys. 31 (10): 1465–1499. doi:10.1023/A:1012682413597.
- Putnam, H. Another Look at Quantum Mechanics, in Philosophy in an Age of Science (Harvard UP, 2012), p. 139-140
- Michael Esfeld, (1999), Essay Review: Wigner’s View of Physical Reality, published in Studies in History and Philosophy of Modern Physics, 30B, pp. 145–154, Elsevier Science Ltd.
- Yu S, Nikolić D (2011). "Quantum mechanics needs no consciousness". Ann. Phys. (Berlin) 523 (11): 931–938. Bibcode:2011AnP...523..931Y. doi:10.1002/andp.201100078.
- Mandel L (1999). "Quantum effects in one-photon and two-photon interference". Rev. Mod. Phys. 71: S274–S282.
- Zeilinger A (1999). "Experiment and the foundations of quantum physics". Rev. Mod. Phys. 71: S288–S297.
- Brukner C, Zeilinger A (2002). "Young’s experiment and the finiteness of information". Philos. Trans. R. Soc. Lond. 360: 1061–1069.
- "The principal argument is that thought processes and consciousness are the primary concepts... [O]ne may well wonder how materialism...could so long be accepted by the majority of scientists. The reason is probably that it is an emotional necessity to exalt the problem to which one wants to devote a lifetime..."
- R. Penrose, The Emporer's New Mind, Penguin Books, 1989, p. 295.
- Victor J. Stenger.The Myth of Quantum Consciousness. The Humanist, May/June 1992, Vol. 53, Number 3, pp. 13-15.
- Carpenter RHS, Anderson AJ (2006). "The death of Schroedinger's Cat and of consciousness-based wave-function collapse". de la Fondation Louis de Broglie 31 (1): 45–52. Archived from the original on 2006-11-30. Retrieved 2010-09-10.
- Bohr, Niels (1958). Atomic Physics and Human Knowledge. Wiley., pp. 73, 81: "The freedom of experimentation, presupposed in classical physics, is of course retained and corresponds to the free choice of experimental arrangement for which the mathematical structure of the quantum mechanical formalism offers the appropriate latitude. ... In the great drama of existence we ourselves are both actors and spectators."
- Heisenberg, Werner (1958). Physics and Philosophy. Harper & Row., p. 32: "[T]he measuring device has been constructed by the observer, and we have to remember that what we observe is not nature in itself but nature exposed to our method of questioning."
- Wolfgang Pauli (1954). "Naturwissenschaftliche und erkenntnistheoretische Aspekte der Ideen vom Unbewussten". Dialectica 8: 283–301. doi:10.1111/j.1746-8361.1954.tb01265.x. as translated in Harald Atmanspacher and Hans Primas, Journal of Consciousness Studies 13(3), 5-50 (2006): "Pauli's ideas on mind and matter in the context of contemporary science": "Once the physical observer has chosen his experimental arrangement, he has no further influence on the result which is objectively registered and generally accessible. Subjective properties of the observer or his psychological state are as irrelevant in the quantum mechanical laws of nature as in classical physics."
- Heisenberg, Werner (1958). Physics and Philosophy. Harper & Row., p. 28. ("[T]he transition from the 'possible' to the 'actual' takes place as soon as the interaction of the object with the measuring device ... has come into play; it is not connected with the act of registration of the result by the mind of the observer. The discontinuous change in the probability function, however, takes place with the act of registration, because it is the discontinuous change of our knowledge in the instant of registration that has its image in the discontinuous change of the probability function.")
- John Honner (2005). "Niels Bohr and the Mysticism of Nature". Zygon Journal of Science and Religion 17–3: 243–253.
- Heisenberg, W, 1990, "Across the Frontiers", (New York: Harpers and Row) requoted from Marin p. 811
- Jeremy Bernstein (1982) Science Observed, New York: Basic Books, ISBN 0-465-07340-9, p.333-340
- ABC News Nightline Face-Off "Does God Have A Future": Deepak Chopra appeals to Roger Penrose
- Bringsford, S. and Xiao, H. 2000.A Refutation of Penrose's Gödelian Case Against Artificial Intelligence. Journal of Experimental and Theoretical Artificial Intelligence 12: 307-329. The authors write that it is "generally agreed" that Penrose "failed to destroy the computational conception of mind."
- In an article at  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."
- Princeton Philosophy professor John Burgess writes in On the Outside Looking In: A Caution about Conservativeness (published in Kurt Gödel: Essays for his Centennial, with the following comments found on 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."
- Quantum Enigma from Oxford University Press
- PHYSICS TODAY: "Is the moon there when nobody looks? Reality and the quantum theory" (pdf)
- "Quantum Cosmology and the Hard Problem of the Conscious Brain" (pdf)
- Mindful Sensationalism: A Quantum Framework for Consciousness.
- Donald Hoffman on Consciousness created reality
- Brian Josephson on QM and consciousness
- "Quantum mechanics and free will: counter-arguments", Martín López Corredoira
- "The Myth of Quantum Consciousness" by Victor Stenger
- "Critique of Quantum Enigma Physics encounters Consciousness", by Michael Nauenberg
- David Chalmers' links to consciousness papers