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The quantum mind/body problem refers to the philosophical discussions of the mind/body problem in the context of quantum mechanics. Since quantum mechanics involves quantum superpositions, which are not perceived by observers, quantum mechanics apparently places observers in a special position.

The founders of quantum mechanics debated the role of the observer, and of them, Wolfgang Pauli and Werner Heisenberg believed that it was the observer that produced collapse. This point of view, which was never fully endorsed by Niels Bohr, was denounced as mystical and anti-scientific by Albert Einstein. Pauli accepted the term, and described quantum mechanics as lucid mysticism.^[1]

Unlike Heisenberg and Bohr, who always described quantum mechanics in logical positivist terms, Hugh Everett took the wavefunction of quantum mechanics as a real description of the world. In the many-worlds interpretation, the memories of the observer splits at every measurement, leading to the subjective appearance of collapse.

This observation was separated from many-worlds interpretation by Eugene Wigner, who proposed that the consciousness of the observer is what causes collapse of the wavefunction, independent of any realist philosophy or splitting observers. Colloquially known as "consciousness causes collapse", this interpretation of quantum mechanics states that observation by a conscious observer is what makes the wave function collapse.

The interpretation identifies 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.

Contents 1 History 1.1 Classical mind/body problem 1.2 Transition to quantum mechanics 1.3 Observation in quantum mechanics 1.4 Decoherence and modern interpretations 1.5 Dualist interpretations 2 "Consciousness causes collapse" 2.1 Criticism 2.2 Alternative interpretations 3 Quantum mysticism, New Age and New Thought belief 4 See also 5 Notes and references 6 Further links and references

[edit] History

In many philosophies, the conscious mind is seen as a separate entity, existing in a realm not described by physical law. Some people 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 including Erwin Schrödinger,^[2] Werner Heisenberg,^[3] Wolfgang Pauli,^[4] Niels Bohr,^[5] and Eugene Wigner^[6]

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 only gives the probability of getting different outcomes, and it only turns into a probability during the act of measurement.^[7]

The nature of observation has often been a point of contention in quantum mechanics,^[8] 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 ^[9], 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.^[10]

[edit] Classical mind/body problem

In classical mechanics the world is measurable, the measurements are revealing the true state of the world, and the behavior is deterministic. Given the initial positions and velocities 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 ^[11][12]

Yet even from a classical perspective many philosophers doubt the material description of a hypothetical Newtonian observer is the only thing you need in order to understand internal experience.^[13][14][15] 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 contrived 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 only becomes apparent to Dennett 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.^[16]

[edit] 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."[11]

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. Quantum mechanics made some dualist ideas about the mind/body problem acceptable again within mainstream science.

[edit] 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. Schrodinger's cat is an illustration of this: after interacting with a quantum system, the wavefunction of the cat describes it as a superposition of dead and alive.

It can be predicted using quantum mechanics that an observer observing a quantum superposition will turn into a superposition of different observers seeing different things. Just like Schrodinger'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. The founders of quantum mechanics were aware of this problem, and each had a different opinion about its resolution:

Albert Einstein, and with him Louis DeBroglie and later David Bohm, believed that quantum mechanics was incomplete, that the wavefunction was only a statistical description of a deeper structure which was deterministic. 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. 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 Podolski and Rosen could not be correct.^[17] Non-local hidden variables are still a possibility, and David Bohm was able to explicitly formulate a nonlocal theory which reproduces the predictions of quantum mechanics. But nonlocal theories are very arbitrary, and the new variables in Bohm's theory are inaccessible to experiments. So most physicists do not accept hidden variable interpretations as compelling.^[18]

Niels 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. This point of view, the Copenhagen interpretation, was shared by Max Born and Werner Heisenberg and 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. 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, past the first incoherent interaction with a complex enough object^[19]

In 1961, Eugene Wigner reformulated Schrödinger's cat using a conscious observer, Wigner's friend. He concluded that the demarcation line which Bohr refused to specify was at the point of conscious experience. Wigner's position was that the wavefunction collapses because consciousness observes it, placing a non-scientific layer at the foundation of quantum mechanics, a non-scientific layer which could be interpreted as mystical, since it treats conscious observation as a separate ingredient.

[edit] Decoherence and modern interpretations

Hugh Everett III proposed an entirely mechanistic interpretation of quantum mechanics that has come to be known as the many-worlds interpretation. In Everett's description, the whole universe is an enormous wavefunction, describing a dizzying multiplying possibility of worlds. In this formalism, observers were to be treated as computers or as any other measuring device, their memories written out on magnetic tape ^[20]. To understand their experiences, you would focus on the answer which these observers would give to questions asked by an external observer. Everett believed that this line of reasoning showed that any interpretational problems in quantum mechanics were entirely philosophical, because he could show that there was no conflict between deterministic evolution of the wavefunction with the subjective randomness experienced by the observers, when analyzed using the theory itself ^[21].

Since the physical description in Everett's picture 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 wavefunction, but not all parts of the wavefunction describe a single observer – only those parts which describe a consistent past of memories. In Everett's picture, the interpretation is a clarification, it tells you which observer you are examining. But the description of the observer is now a major chunk of the description of the world--- it includes a lot of extra information not present in the original wavefunction.^[22]

This extra information includes most observable parameters in our universe. For example, if the universe started out perfectly homogeneous and isotropic, the universal wavefunction would still be homogeneous and isotropic. But for any observer, the description would be irregular describing a different pattern of galaxies, stars and planets. The information which specifies the observer specifies the positions of all those stars, the distance to Jupiter, the location of the moon in its orbit, the contents of today's newspaper, etc. None of this is in the universal wavefunction, that object is only a quantum superposition of all possible worlds. Most of the nontrivial information is in the history of past random events.

Everett's approach has been elaborated into a field of study called decoherence, which attempts to identify the way in which classical behaviour emerges from quantum mechanics when the systems become large.^[23]

[edit] Dualist interpretations

The description of the observer in decoherence approaches, 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.

The presence of large amounts of additional information has been interpreted as a component associated with the consciousness of the observer, because it is data which is associated with the observer, not with the matter from which the observer is built. Since this includes most information about the universe, considering the quantum mechanical description to be complete leads to a reevaluation of the nature of the observer.^[24]

[edit] "Consciousness causes collapse"

The involvement of consciousness in the collapse of the wave function 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.^[25]

This interpretation attributes the process of wave function collapse (directly, indirectly, or even partially) to consciousness itself.

The consciousness causes collapse interpretation was Wigner's motivation for introducing Wigner's friend by asserting that collapse occurs at the first "conscious" observer. Supporters assert this is not a revival of substance dualism, since (in a ramification of this view) consciousness and objects are "entangled" and cannot be considered separate.

[edit] Criticism

Some critics say that this theory does not explain which things have sufficient consciousness to collapse the wave function ("Was the wave function waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer for some highly qualified measurer - with a PhD?"^[26]). It is also not clear whether measuring devices might also be considered conscious.

Opponents^[who?] assert that it is unfalsifiable, and also does not simplify our physical understanding of the universe, and is therefore scientifically uninteresting^{[citation needed]}.

Wigner believed that consciousness is necessary for the quantum mechanical process. See Consciousess and measurement. There are other possible solutions to the Wigner's friend thought experiment which do not require consciousness to be different from other physical processes. See, Consciousness and Superposition.

[edit] Alternative interpretations

The Many worlds interpretation avoids the need to postulate that consciousness causes collapse — indeed, that collapse occurs at all. Instead, observation of a superposed system sends the observer into a superposition, each element of which sees a (different) single outcome to the experiment. See Wigner's friend in Many Worlds.

According to objective collapse theories, wave function collapse occurs when a superposed systems reaches a certain objective threshold of size, complexity etc. Thus, the fact that observers see an un-superposed classical world is a side-effect of the fact that they are macroscopic, and collapse can occur in the absence of observers.

[edit] Quantum mysticism, New Age and New Thought belief

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.^[27]

Fritjof Capra popularizes the subject with The Tao of Physics.^[28] 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.

The view is also presented in various aspect of the New Thought Movement such as the popular and controversial documentaries What the Bleep Do We Know!? and The Secret, alongside some unrelated biological discussions, and is a major plot point in Greg Egan's novel Quarantine, as well as playing a significant role in Charlie Stross's novel The Atrocity Archives.

[edit] See also

• Measurement in quantum mechanics
• Interpretation of quantum mechanics
• Many-worlds interpretation
• Quantum indeterminacy
• Quantum mysticism
• Quantum mind
• Quantum Zeno effect
• Association for the Scientific Study of Consciousness

[edit] Notes and references

1. ^ Juan Miguel Marin (2009). "‘Mysticism’ in quantum mechanics: the forgotten controversy". European Journal of Physics 30: 807–822. doi:10.1088/0143-0807/30/4/014.  link, summarized here
2. ^ By Michel Bitbol, Olivier Darrigol, Erwin Schrödinger,Institut autrichien de Paris
3. ^ from[1] "Quantum theory has led the physicists far away from the simple materialistic views that prevailed in the natural science of the nineteenth century" Werner Heisenberg, Physics and Philosophy, (New York: Harper & Row Publishers, (1962), 128
4. ^ "I confess, that very different from you, I do find sometimes scientific inspiration in mysticism … but this is counterbalanced by an immediate sense for mathematics." -- W. Pauli, from[2]
5. ^ John Honner (2005). "Niels Bohr and the Mysticism of Nature". Zygon Journal of Science and Religion 17-3: 243–253. 
6. ^ Wigner -, Eugene -; Henry Margenau - (1967-12 -). "[http://link.aip.org/link/?AJP/35/1169/1 - Remarks on the Mind Body Question, in Symmetries and Reflections, Scientific Essays -]". American Journal of Physics - '35 - (12 -): 1169–1170 -. doi:10.1119/1.1973829+++ (inactive 2009-10-19). http://link.aip.org/link/?AJP/35/1169/1 -. Retrieved 2009-07-30 -. 
7. ^ This is an abbreviated paraphrase of the section entitled "The Language of Quantum Mechanics" in Wigner "Remarks on the Mind-Body Question"
8. ^ 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"
9. ^ pay link to Einstein letter Laue, Schrodinger and Einstein dissent
10. ^ Wigner, E. "Remarks on the Mind-Body Question", Symmetries and Reflections
11. ^ 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"
12. ^ Haeckel, Ernst Heinrich Philip (1992). The Riddle of the Universe. Prometheus Books. ISBN 0879757469, 9780879757465. 
13. ^ Kirk, Robert. 1974. "Sentience and Behaviour", Mind, vol. 83, pp. 43–60.
14. ^ Nagel, Thomas. 1970. "Armstrong on the Mind", Philosophical Review, vol. 79, pp. 394–403.
15. ^ Nagel, Thomas. 1974. "What is it Like to Be a Bat?" Philosophical Review, vol. 83, pp. 435–450.
16. ^ Dennett, Hofstadter, "The Mind's I" Basic Books
17. ^ Amir D. Aczel, "entanglement"
18. ^ 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
19. ^ Von Neumann, J., "Mathematical Foundations of Quantum Mechanics"
20. ^ 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
21. ^ De Witt, B. and Graham, M. "The Many Worlds interpretation of Quantum Mechanics", Princeton University Press
22. ^ Quoting Bohm/Hiley: It is evident that in a series of measurements, the number of partial awarenesses must multiply indefinitely. There are correspondingly many possible branches consisting of such sequences of partial awarenesses" p.299
23. ^ Gell-Mann, M., "The Quark and the Jaguar", pp. 135-176
24. ^ 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
25. ^ Schreiber, Z. The Nine Lives of Schrödingers's Cat
26. ^ Bell, J.S., 1981, Quantum Mechanics for Cosmologists. In C.J. Isham, R. Penrose and D.W. Sciama (eds.), Quantum Gravity 2: A second Oxford Symposium. Oxford: Clarendon Press, p.611.
27. ^ Heisenberg, W, 1990, "Across the Frontiers", (New York: Harpers and Row) requoted from Marin p. 811
28. ^ Jeremy Bernstein (1982) Science Observed, New York: Basic Books, ISBN 0-465-07340-9, p.333-340

[edit] Further links and references

pro

• 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

con

• "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", Martín López Corredoira

neither

• David Chalmers' links to consciousness papers
• [3] quantum-mind