minds, brains, and quantum mechanics

The Southern Journal of Philosophy (1995) Vol. XXXIII

Minds, Brains, and Quantum Mechanics

Niall Shanks East Tennessee State University

I think this maybe brings us on to the question of how quantum mechanics can ever have been misused for explaining extrasensory perception, for explaining the phenomenon associated with Uri Geller, spoon bending, telepathy, precognition, and all those paranormal events which of course have great public interest .... All of this is related to the question of whether consciousness plays a role in fundamental physical phenomena.’

John Taylor

I. INTRODUCTION

The orthodox (von Neumann) interpretation of quantum mechanics gives a special role to the mind or consciousness of the observer. Sometimes this claim is developed along quite fanciful idealistic lines.2 In the quantum theory-unlike other physical theories-the “conscious observer” is not a passive member of the audience, watching physical events being played out on the experimental stage. In a special sense to be explained below, the conscious observer is an important actor on this stage.

Most scientists and many philosophers regard the quantum theory as one of our current best physical theories. Similarly, many scientists and philosophers hold to physicalism as an ontological thesis. I t will be argued below tha t the attempt to understand the references to consciousness that appear in orthodox quantum mechanics in physicalistic terms (either from the standpoint of reductive or non-reductive physicalism) leads t o a number of disquieting puzzles and conundrums. In the light of the analysis, some seemingly plausible options will be presented. But reasons will be given for supposing that none

Niall Shanks is Assistant Professor of Philosophy at East Tennessee State University. He earned his Ph.D. from the University of Alberta in 1987. His primary research interests include philosophy of physics, philosophy of physiology, and philosophy of mind.

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of them are entirely adequate. I t will be concluded that quantum mechanics remains a deeply puzzling theory even when formulated so as to avoid the toils of Cartesianism-toils which so ensnared early attempts to explain the special role played by the conscious observer from the standpoint of this physical theory.

11. ROLE OF CONSCIOUSNESS IN QUANTUM MECHANICS

In order to clarify the issue as to why some quantum theo- rists felt compelled to introduce a special role for consciousness in a fundamental physical theory, i t will be useful to consider the basic axioms upon which the quantum edifice is erected.

Consider the following axiomatization of non-relativistic elementary quantum mechanics3:

(1) The State Space. There is a mapping S:Q+H, from individual systems Q in the domain of quantum mechanics, t o Hilbert spaces H whose unit rays completely de- scribe the physical states of those individual systems. (2) The Observables. There is a mapping O:A+A, from quantum mechanical observables A associated with an individual system to Hermitian operators A on the Hilbert space H associated with that system. (3) The Schroedinger Equation. The time development of the state vector w is determined by: H y = i h %I&, where H is the Hamiltonian operator and h is Planck’s constant divided by 271. (4) The Projection Postulate. If measurement of an observable A on system Q yields eigenvalue a, the physical s ta te of Q immediately after measurement is the eigenstate wi of A corresponding t o eigenvalue ai. (Ignoring de- generacy). ( 5 ) The Born Rule. If the quantum state of a system Q is:

where (Oi l is a complete orthonormal set of eigenstates of observable A with corresponding eigenvalues (a,), then I c, I gives the probability that the eigenvalue of A imme-

diately after measurement will be found to be a,.

w = ci ci 0,

In the above axiomatization of quantum mechanics, Axioms (3) and (4) are the quantum mechanical rules that govern the assignment of quantum states to quantum systems. They will be referred t o as state assignment rules . State assignments in terms of the Schroedinger equation are deterministic, unitary,

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and continuous. State assignments in accord with the Projec- tion Postulate are, in general, non-unitary, indeterministic, and discontinuous. Prima facie, the existence of two such very different state assignment rules leaves scope for conflicting state assignments in any number of interesting physical situa- tions. The possibility of conflicting s ta te assignments gives rise to the measurement problem. This problem is typically il- luminated through the presentation of various paradoxes.

A Measurement Paradox Perhaps the best known of these paradoxes is the Paradox

of Schroedinger’s Cat: A felicidal maniac hooks a cat up to a device containing an unstable atom. If the atom decays, this event will be detected and a circuit will close resulting in the electrocution of the cat. The cat-plus-fiendish device is placed into a sealed opaque container-so no one can observe events in the box-and left there for one hour. The probability that a decay event will occur in this time period is 0.5. What is the state of the cat at the end of the hour time period, but immediately prior to any observation? Let yii be the wave function corresponding to the eigenvalue “live cat,” and let vj be the wave function corresponding to the eigenvalue “dead cat.” Ac- cording to Axiom [3], the state of the cat a t the end of the hour is: $ = ci yii + c, yij. In such a state, I c. I = I cj I = 0.5. But the cat, since i t cannot be both alive and dead, is said to be neither alive nor dead. The state of the cat is indeterminate with respect to the property of vitality!

Yet, it remains a fact that whenever the cat is examined, it is always either alive or dead-we never see a cat in limbo. According to Axiom (4), when the observer actually inspects the cat, the state “collapses” or “reduced’ either to v. or yi., on the basis of the eigenvalue o b ~ e r v e d . ~ I t is known that these “reductions of the wavepacket” cannot in general be described by the Schroedinger equation.

The orthodox interpretation of the standard axiomatization of quantum mechanics attempts to evade the possibility of conflicting state assignments by restricting the domain of application of the Schroedinger equation to physical processes tha t are not measurements. Where physical processes constitute measurement interactions, states are to be assigned to systems on the basis of the Projection Postulate. For this solution to be satisfactory, criteria must be formulated that will enable a distinction t o be drawn between measurement interactions and other physical processes. While the provision of such criteria is not unproblematic, it is generally assumed that the distinction can be drawn.

In the orthodox interpretation two distinct strategies have been considered in connection with the issue of the differentia- tion of measurement interactions from other physical pro-

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cesses. The first of these is the micro-macro strategy which ap- peals to the classical describability of macroscopic measuring device^.^ The basic idea is tha t measurement interactions occur when a macroscopic system interacts with a microscopic system. In such cases, Axiom (4) will be the appropriate state assignment rule. For micro-micro interactions, Axiom (3) is to be used instead. On such a view, the property of being classically describable will be a n emergent property of macroscopic objects. But this strategy is faced with a t least four difficul- ties: (1 ) Exactly how is the distinction between macro-systems and micro-systems t o be drawn? Where? Some investigators have suggested tha t the boundary between the two domains should be drawn at a scale of the order of cm. But this seems arbitrary. Especially in light of the fact tha t (2) there are known macroscopic quantum effects (e.g., superconductiv- ity and superfluidity, a s well a s the coupling of particle systems over macroscopic spacelike separat ions of t h e kind underlying the Einstein-Podolsky-Rosen Paradox). (3) the micro-macro strategy seems to include as measurement interac- t ions, events t h a t intuit ively do not seem to be such-for example, chance collisions between photons and battleships, or electrons and oak trees! (4) the micro-macro strategy seems to make the property of being classically describable a n emergent property of systems of a certain (macroscopic) size-unless this is the case, it is hard to see how a lot of micro-systems making up a macro-system, could have the property of classical describability t h a t none of the micro-systems have indi- vidually. For these reasons, I reject the micro-macro strategy.

The second strategy-the psychological strategy-involves a basic distinction between the observing subject and the object observed. Von Neumann put it thus:

That is, we must divide the world into two parts, the one being the observed system, the other the observer. In the former we can follow up all physical processes (in principle at least) arbitrarily precisely. In the latter, this is meaningless .... That this boundary can be pushed arbitrarily deeply into the interior of the body of the actual observer is the content of the principle of psycho-physical parallelism-but this does not change the fact tha t in each method of description the boundary must be put somewhere, if the method is not to proceed vacuously, i.e., if a comparison with experiment is to be possible. Indeed experience only makes statements of this type: a n observer has made a certain (subjective) observation; and never any like this: a physical quantity has a certain value. (von Neumann 1955, 420)

Von Neumann proceeds to claim that when the observer interacts with systems in the observed world, states are t o be assigned in accord with Axiom (4).

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What aspect of the observer is crucial to this distinction between the observer and the observed? Wigner comments:

When the province of physical theory was extended to encom- pass microscopic phenomena, through the creation of quantum mechanics, the concept of consciousness came to the fore again: it was not possible to formulate the laws of quantum mechanics in a fully consistent way without reference to the consciousness .... even though the dividing line between the observer, whose consciousness is being affected, and the observed physical object can be shifted towards the one or the other to a consider- able degree, it cannot be eliminated. (Wigner 1962, 2851

But how does the orthodox interpretation of quantum mechanics conceive of the consciousness of the observer?

Von Neumann, in discussing the dividing line between the observer and the observed, considers a division of the world into three parts: I is the system observed, I1 is the measuring instrument, and I11 is the actual observer. He describes one of the ways of making the division as follows: “I was everything up to the retina of the observer, I1 his retina, nerve tracts and brain, I11 his abstract ‘ego’.” This seems to be strongly sugges- tive of some species of Cartesian dualism-that the “self“ or “consciousness” might be distinct from the physical brain, nerve tracts and all! If this is the case, then in addition to quantum mechanical peculiarities concerning measurement interactions, there would be all the traditional worries about mind-body interaction. I will have more to say about issues connected with the nature of the mind below, for i t seems to me tha t we are not forced to adopt substance dualism even if we wish to give “consciousness” a special role in physics.

But regardless of how consciousness is characterized, we should not lose sight of the rationale for its introduction: the intervention of the consciousness of the observer is what dif- ferentiates measurement interactions from all other physical processes. Von Neumann was an empiricist. In the long quota- tion above, i t is clear tha t he believes tha t a distinction between measurement interactions and other interactions must be drawn if quantum mechanics is to face the tribunal of experience. According to Von Neumann, the statements in terms of which the theory is to be reckoned are subjective reports of values observed for various quantities of interest. In these terms, the quantum theory is a theory of subjective observa- tions and their probabilities-and the distinction between measurement interactions and other physical processes is drawn to enable the theory to “save the (subjective) phenomena.’’

This particular empiricist construal of quantum mechanics was not the result merely of an arbitrary philosophical whim.

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It is likely t h a t Von Neumann was led to this view by his “proof” of the impossibility of supplementing quantum mechanics with hidden variables-parameters which would ensure that all the quantum mechanical observables associated with a given system of interest would take simultaneous exact values in the absence of conscious observing subjects.6 No quantum state can determine all such values: in general, if the state of a system is an eigenstate of some observable A, then it will determine a unique eigenvalue, upon observation, for observable A, but not for observables B which do not commute with A. Such observables will be “incfeterrninate” or “valuele~s.”~ It is an important tenet of orthodox quantum mechanics that there are no hidden variables-this is the No Hidden Variables The- sis. If there are no hidden variables, the only values to be spoken of will be values for quantities upon observation. And the only probabilities will be probabilities for various values to be observed. Given the von Neumann interpretation, such observed values will be consciousness-dependent.

Hence Von Neumann’s reluctance to speak of physical quan- t i t ies taking definite values independently of observation. Which observables associated with a given system take definite values on a given occasion will depend on which experiment the observer chooses t o perform-and recall that according to orthodox quantum mechanical lore, i.e., the orthodox interpretation of the Heisenberg uncertainty relations, it is not possible for observers to perform experiments which determine simultaneous exact values for non-commuting observables. Secondly, given an experiment to determine a value for an observable A, precisely which definite eigenvalue is revealed upon measurement will depend on the result of the inherently probabilistic collapse of the wavepacket prompted by the intervention of the consciousness of the observer.

Philosophical Puzzles Von Neumann’s version of the quantum theory seems to

manifest the following three features: (1) i t is committed to dualism-consciousness, the abstract “ego”-seems to be something separate from the observer’s neurological apparatus, (2) quantum theory ends up as a theory of the observer’s subjective measurement experiences and their probabilities, and (3) at any time, for which observables a quantum system takes definite values depends on the experimental choices of the observer, and the values taken by those observables depend (probabilistically) on the intervention of the observers’ consciousness.

Taken together, these three points, a t least on the face of it, seem to be somewhat embarrassing. They suggest tha t quantum mechanics, one of our current best physical theories, may not be acceptable from a physicalistic perspective. And, the

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reason that the theory may be physicalistically unacceptable is that it seems to embody some features traditionally associated with idealistic metaphysical theories. That observables may only take definite values due to the intervention of the consciousness of the observer is certainly reminiscent of Berkeley’s dictum: Esse ist percipi aut percipere.

The question t o be considered now is this: since i t is possible to refer to the consciousness of the observer without being committed t o some form of Cartesian dualism, is i t possible tha t the apparent element of idealism in orthodox quantum mechanics could be rendered acceptable to physicalism?8

111. REDUCTIVE PHYSICALISM

But what is physicalism? There are two species of physicalism worthy of consideration. The first is reductive physicalism. According to Hartry Field, physicalism is:

... the doctrine that chemical facts, biological facts, psychological facts and semantical facts are all explicable (in principle) in terms of physical facts. The doctrine of physicalism functions as a high- level empirical hypothesis, a hypothesis that no small number of experiments can force us to give up. (Field 1980, 91-92)

As such, physicalism stands opposed to theories such as Vital- ism (the doctrine that there exist irreducibly biological facts) and Cartesianism (according to which there are irreducibly psychological facts).

In connection with Cartesianism, one can distinguish between substance dual ism (Cartesianism proper) and property dual ism (according to which some physical objects have irreducibly non-physical, mental properties). Similarly, with respect to Vitalism, one can distinguish between substance u i ta l i sm (perhaps involving reference to a “vital force” or Bergsonian klan v i t a l ) and property v i ta l i sm (according to which some physical objects have irreducibly non-physical, biological properties). Jus t as one can reject substance dualism without rejecting property dualism, so one can reject substance vitalism while being committed t o property vitalism-though not, of course, if one is committed to reductive physicalism.

For by “irreducible facts” (which may be facts about the properties of objects), Field makes it clear that he has in mind facts that are not explicable in terms of non-biological or non- psychological, physical facts. And Field adds: “I believe that physicists a hundred years ago were justified in accepting mechanism, and that, similarly, physicalism should be accepted until we have convincing evidence that there is a realm of phenomena it leaves out of account” (Field 1980, 92).

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I n order to illustrate the force of his conception of physicalism, Field considers the case of a woman who h a s two sons, one of whom has hemophilia. One of the sons must have been derived from a n ovum t h a t had a gene for hemophilia. Field comments:

We should not rest content with a special biological predicate “has- a-hemophilic-gene”- we should look for nonbiological facts (chemical facts and ultimately physical facts) that underlie the correct application of this predicate. That at least is what the principle of physicalism tells us, and it can hardly be doubted that this principle has motivated a great deal of profitable research into the chemical foundations of genetics. (Field 1980, 92)

It should be clear now why this sort of physicalism deserves the name reductive physicalism. For physicalism so conceived construes the explication of biological and psychological facts as involving a reduction of those facts to basic physical facts. For Field it is a working hypothesis t h a t t h e basic facts in terms of which other facts a re to be explicated are facts concerning the physical objects, properties and relations referred to in our current best physical theories (our basic physical ontological commitments), and it is a working hypothesis t h a t reference to other objects, properties and relations is legiti- mate only insofar as they are expected to be reducible (in principle) to our basic physical ontological commitments.

Reductive physicalism has the following consequence: there are no non-physical, menta l , or biological objects, a n d no physical objects (brains, for instance) have irreducibly mental or biological properties. This is a consequence which is relevant to any interpretation of quantum mechanics, such a s von Neumann’s, which embodies the idea tha t there is a n abstract ego which exists independently of the neurological appa- r a t u s . In such in te rpre ta t ions of q u a n t u m mechanics, quantum systems come to take definite values for observables as a consequence of their interaction with the consciousness of the observer. Such properties of quantum systems are mind- dependent in the sense tha t they would not obtain were it not for appropr ia te measurements , a n d according t o von Neumann, there a re no measurements without the intervention of consciousness. Reductive physicalism would seem to de- prive von Neumann of t h e abs t rac t ego required for his account of measurement interactions-and hence for his account of how quantum mechanics saves the phenomena.

Reductive Physicalism and the Mind The possibility remains, however, t h a t consciousness may

be analyzed and explicated in some manner consistent with t h e tene ts of reductive physicalism. Two possibilities t h a t

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spring to mind are: (1) the mind-brain identity hypothesis, according to which minds, taken to be identical with physical brains, exist and are capable of causing physical effects (e.g., reductions of wavepackets); and ( 2 ) the eliminatiue materialist hypothesis, according to which (some) physical, neuroanatomical structures exist and are similarly capable of causing physical effects.

I t is possible tha t the mind is identical with the physical brain. So that the consciousness of the observer is to be analyzed in terms of purely physical processes in the brain. Alter- natively, t he mind may be t reated, as i t is in eliminative materialist theories, as an entity to be dispensed with in favor of an analysis of neuroanatomical structure couched in non- mental language (so that talk of “minds” is to be abandoned, along with the rest of “Folk Psychology,” as mere superstitious talk about the serious subject matter of neuroanatomy). If this was the case, then quantum mechanical references to consciousness, while something of a theoretical embarrassment (like references t o “the hand of God” in Newtonian physics), may one day be replaced with appropriate, non-mental, neuroanatomical analyses. From the point of view of both of these reductive physicalist hypotheses, the quantum mechanical properties of a system will not be “consciousness-dependent” or “mind-dependent,” rather they will be ultimately “brain-dependent.”

But there is a problem here since reductive physicalism makes reference to physical objects, properties, and relations spoken of in our current best physical theories, but neuroanatomy is a biological science concerning the properties of a n evolved biological entity-and the basic facts of neuroanatomy are biological facts. So the question arises as to how we are to treat the mind-brain identity theorist’s or eliminative materialist’s account of facts concerning the brain ex- cept ultimately in terms of basic quantum mechanical facts (since quantum mechanics is generally regarded as a basic physical science constituting our current best physical theory of microstructure). If the basic facts here are irreducible, biological, neuroanatomical facts, then from the standpoint of reductive physicalism, a species of‘ property vitalism will have won the day. To paraphrase Field, the reductive physicalist will not rest content with a special biological predicate “has-a- brain.” Such a physicalist will seek the non-biological, basic physical facts that underlie the correct use of that predicate.

But here is the difficulty. In orthodox quantum mechanics there are no hidden variables to provide quantum objects with consciousness- o r brain-independent, determinate physical properties upon which to found any such basic physical account of the facts of neuroanatomy. Yet, the reductive physicalist will be inclined t o say that while consciousness may be a

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property of a complex macroscopic neuroanatomical system, surely it is a property that must ultimately be understood in terms of the basic physical properties of, and relations tha t hold between, the (micro) physical parts of the system.

A Dilemma for the Reductive Physicalist In view of this situation, there seems to be a dilemma for

the reductive physicalist. Such physicalism requires tha t all facts-in particular, those about the neuroanatomy of the brain-be explicable (in principle) in terms of basic physical facts. But which type of physical fact? I t is tempting to say that the relevant facts will be microphysical facts concerning the atomic structure of the brain. But in orthodox quantum mechanics there are no mind- or brain-independent microphysical facts.

While microphysical properties are not candidates for the purposes of reduction-since they are all illegitimately brain- dependent-the possibility remains tha t neuroanatomical properties could be reduced to irreducibly emergent, mind- or brain-independent, macrophysical properties. But if this is the case, then the psychological strategy, which attempts to differ- entiate between measurement interactions and other physical processes on the basis of an appeal to the consciousness of the observer, would appear to reduce to the micro-macro measurement strategy discussed-and dismissed-in Section I1 above.

Preserving the integrity of the psychological strategy seems to involve viewing the basic facts as being emergent facts about highly complex, organized, macroscopic neuroanatomical systems, such as brains, tha t are simply not reducible to, o r even supervenient on, such other physical facts as there may be. Call this position brain-based e m e r g e n t i ~ m . ~ If brain-based emergentism is t rue , the physicalist may have escaped Cartesianism, but at the price of making neuroanatomy-a branch of biology-the queen of the sciences.'O

However, brain-based emergentism is not an appealing possibility, for then macroscopic neuroanatomical laws and facts would not be reducible to more basic physical laws and facts, instead they would be the most basic laws and facts. This is surely a Pyrrhic victory, for a universe whose properties are ultimately brain-dependent, is hardly more appetizing than one whose properties are mind-dependent. For example, what was the world like before animals-humans in particular- evolved brains? How were wavepackets reduced so that matter could become suitably arranged for self-organization to be a possibility, and for evolving life-forms t o appear in the first place? Perhaps, then, reductive physicalism must be abandoned. Perhaps there are psychological and/or biological facts that are not reducible in principle to more basic physical facts. But wouldn't th is amount t o a return to unscientific philo-

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sophical theories such as Cartesianism and Vitalism? Much hinges here on how physicalism is construed.

w. NON-REDUCTIW PHYSICALISM

The other species of physicalism is non-reductive physical- i sm. According to this hypothesis, while the only admissible objects are physical objects (so substance dual i sm and substance vitalism are ruled out, for example), i t is nevertheless permitted that (some of) those physical objects may “possess” non-physical properties and relations-as in property dualism and/or property vitalism. In this case there will be facts about (some) physical objects t ha t will not be reducible t o basic physical facts concerning those objects-for example, those facts spoken of in microphysics.

Concerning attempts to reduce biological properties, Ernst Mayr notes:

Attempts to ‘reduce’ biological systems to the level of simple physico-chemical processes have failed because during the reduction the systems lost their specifically biological properties. Living systems ... have numerous properties that are simply not found in the inanimate world. (Mayr 1988, l )

Such biological properties that are not found in the inanimate world result from the hierarchical complexity and organization of evolved living systems. Biological systems are physical systems, but they have properties that cannot be reduced to more basic, non-biological, physical properties. Commenting on the properties of hierarchically organized biological organisms, Mayr suggests that:

Systems at each hierarchical level have two properties. They act as wholes (as though they were a homogeneous entity), and their characteristics cannot be deduced (even in theory) from the most complete knowledge of the components, taken separately or in other combinations. In other words, when such a system is as- sembled from its components, new characteristics of the whole emerge tha t could not have been predicted from a knowledge of the constituents. (Mayr 1988, 15)

If these irreducible biological properties exist-in accord with some version of property vitalism-then how are they related to the objects and properties spoken of in the basic physics of inanimate matter? One suggestion explored by non-reductive physicalists is that the relevant relation is one of non-reductive supervenience. To say that properties of Type- A supervene on properties of Type-B is to say that any differ-

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ence with respect to Type-A properties implies a difference with respect to Type-B properties, but not necessarily vice versa.

On this view, for example, one might suppose that changes with respect to biological properties will imply changes with respect t o biochemical properties-and ultimately more basic physical properties. But the converse does not hold-there are many changes a t the quantum mechanical level (reductions of the wavepackets of electrons in atoms comprising cells) which are not reflected at the level of biological properties."

Since the issue of supervenience has been raised, i t will be helpful to distinguish between two types of property vitalism: hard property vitalism and soft property vitalism. Hard property vitalism is the thesis tha t there exist irreducible, non- physical, biological properties tha t do not supervene on more basic physical properties. Soft property vitalism is the thesis that there exist irreducible, non-physical, biological properties which nevertheless do supervene on more basic physical prop- ert ies. Non-reductive physicalism will be thwarted if hard property vitalism turns out to be true.

Similar remarks can be made with respect to psychological properties such as consciousness. In addition to irreducible biological properties, (some) physical objects may have irreducible psychological properties. Conscious experience is commonly thought to supervene on neural properties, since any difference in conscious experience implies a difference in its neural sub- s t ra tum, although, once again, the converse does not hold. Small changes in neural states need not be reflected in conscious experience.12 The issue as to whether consciousness can be explicated in non-reductionist physicalist terms is an open question that should not be ignored.

A Puzzle for Non-Reductive Physicalism Unfortunately, from the standpoint of the orthodox interpre-

tation of quantum mechanics, i t is by no means clear tha t i t helps t o be a non-reductive physicalist. In the quantum mechanical context, the non-reductive physicalist maintains that consciousness-needed to reduce wavepackets-while neither reducible nor eliminable, nevertheless supervenes on a neuroanatomical substratum. But what of this neuroanatomical substratum?

Are neuroanatomical properties-a species of evolved, biological property-to be taken as basic, irreducible, non-supervening properties (properties of complex, highly organized, evolved biological systems)? If so, we seem t o be back to some version of hard property vitalism. Or do these neuroanatomical properties themselves supervene on-though they need not be reducible to-more basic microphysical properties?

It is tempting to think that the neuroanatomical properties must themselves supervene on the properties of the micro-

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physical components of the brain-after all, the brain exists as a brain (as opposed to some other organ or even a lump or cloud of inanimate matter) only because many atoms are local- ized within fairly small spatial regions, and are configured and related to each other in fairly well determined and determinate (complex and highly organized) ways.

But in the orthodox interpretation of quantum mechanics, there are no hidden variables in terms of which one can provide an account of consciousness-independent, determinate, properties of microphysical systems-basic physical properties on which other properties could supervene. To put i t bluntly, in orthodox quantum mechanics, wavepackets of atomic systems are reduced through the intervention of consciousness- this is how those systems a re said to a t ta in determinate physical properties. And according to the non-reductive physicalist, consciousness itself supervenes on neuroanatomical properties.

But according t o the non-reductive physicalist hypothesis, neuroanatomical properties must themselves supervene on the basic physical properties of the microscopic components of the neuroanatomical apparatus. These latter microphysical properties exist only through the intervention of consciousness- they are consciousness-dependent. So the determinateness of the (atomic) parts of the brain seems to presuppose the whole brain itself (as the evolved, neural substratum upon which [wavepacket reducing] consciousness can supervene).

Put another way, how, prior to the evolution of conscious beings, did matter attain the determinate microphysical properties (through wavepacket reductions) that are the precondi- tions for the emergence of living systems, which may ultimately evolve the neuroanatomical properties upon which the property of consciousness can supervene? There appears to be no easy answer to this question from the standpoint of the orthodox interpretation of quantum mechanics. And that being so, the spectre of hard property vitalism-in the form of irreducible, non-supervening neuroanatomical properties-appears to be lurking in the wings. This may be an advance on von Neumann’s Cartesianism, but it is bad news for non-reductive physicalism.

V. ALTERNATIVES?

If the orthodox interpretation of quantum mechanics cannot be reconciled with either reductive or non-reductive physicalism, then perhaps physicalism (in some form) can be saved through the adoption of a non-standard interpretation of quantum mechanics. For instance, it is possible that , contrary to the dictates of the orthodox interpretation of quantum me-

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chanics, there are hidden variables that account for the consciousness-independent, physical properties of quantum systems. And, in terms of which, the facts of consciousness or macroscopic, complex neuroanatomy may be explained-either through relations of reduction or supervenience. I t is also possible that quantum mechanics admits of a non-standard interpretation-but one not committed to hidden variables or quantification over the consciousness of the observer.

The first possibility is arguably quite unappealing since re- cent work on Bell’s Theorem suggests that the price to be paid for introducing such hidden variables into quantum mechanics would be relativistically unacceptable action-at-a-distan~e.’~ At least in the short-term, this would seem to dash hopes for a unified physical science. Moreover, to go this route is to concede the inadequacy of the orthodox (von Neumann) approaches to the interpretation of quantum mechanics. I t is perhaps unfair to dismiss research on hidden variables theories-and this is certainly not the place to discuss the issue at any length-but i t remains t rue t h a t many physicists a r e highly skeptical of the ultimate viability of hidden variables approaches (e.g., the recently ressurrected Bohm theory). The introduction of action-at-a-distance is for some simply too high a price to be payed in exchange for removing the conscious observer off the natural stage.

According to the second option, perhaps there exists an acceptable non-standard interpretation of quantum mechanics- but one not committed to hidden variables. Notice tha t to go this route is to once again concede the inadequacy of the orthodox interpretation. One non-standard interpretation explored in the l i terature is the so-called many-wor lds interpretation of quantum mechanics. I t is beyond the scope of this article to examine this interpretation in detail. The following remarks seem pertinent: in this interpretation of quantum mechanics, there are no reductions of the wavepacket. Rather, in the context of the ca t paradox, when the wavepacket for the cat evolves into the superposition of the “live” and “dead” cat states, the entire universe splits into two parallel universes, one containing a dead cat plus everything else, the other containing a live cat plus everything else. Apart from worries about gross violations of the law of conservation of mass-energy, this interpretation seems t o involve such a large dose of Ockham’s “hair restorer,” in the form of needless multiplication of entities, as to be completely lacking in plau- sibility! (Intuitions vary here, and maybe this interpretation is the lesser of evils).

I do not rule out either of the above unorthodox interpretations of quantum mechanics. But I do note tha t they are the two most commonly discussed alternatives to the orthodox interpretation, and neither is unproblematic from both a physi-

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cal and a metaphysical standpoint. That is t o say, neither of the alternative interpretations seems to offer much of a net gain, in terms of demystification, over the von Neumann interpretation. Put another way, it is one thing to reject the orthodox interpretation, bu t quite another t o pu t something sensible in its place.

VI. CONCLUSION

The orthodox interpretation of quantum mechanics places the conscious observer on the stage of nature. In its original form, consciousness was conceived of as something separate from the neurological apparatus of the observer-in a manner reminiscent of Cartesianism. Since many philosophers and scientists reject Cartesianism in favor of a physicalistic view of the world, I have explored the possibility of saving orthodox quantum mechanics from Cartesianism by examining whether it is possible to construe consciousness in physicalistically acceptable terms.

From the standpoint of reductive physicalism-and given the No Hidden Variables Thesis-it was discovered tha t the basic physical properties to which consciousness was either to be reduced to, or eliminated in favor of, were either (1) macroscopic neuroanatomical (biological) properties, and these types of property are not the basic physical properties spoken of in our current best physical theories; or (2) emergent macroscopic physical properties, in which case the psychological strategy for differentiating measurements from non-measurements collapses into the micro-macro strategy-a strategy t h a t is known to be independently problematic.

From the standpoint of non-reductive physicalism (and given, once again, the No Hidden Variables Thesis), it appears that consciousness may supervene, in a non-reductive way, on neuroanatomical properties. Nevertheless, the question arises as to the relation of the neuroanatomical properties t o the properties of their constituent microphysical systems. The relation could be one of reduction or supervenience. But either way, the microphysical properties are, in the orthodox interpretation, consciousness-dependent. And i t was seen to be a puzzle as to how matter could have gained the determinate properties (through wavepacket reductions) which are the pre- conditions for the appearence of beings capable of evolving consciousness, without presupposing the existence of consciousness in the first place.

While i t is tempting to reject the orthodox interpretation, its main rivals can hardly be said to provide significant gains on the demystification front, involving as they do either commitment to action-at-a-distance, or commitment to a multiplic-

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ity of empirically inaccessible universes. In view of this, some will be tempted to abandon the explanatory enterprise. Indeed, many have in fact lapsed into an instrumentalist sulk, mum- bling the magic quantum mechanical mantra, “It just works.” But this is a long way from the high ideals of physicalism of any stripe, embracing as it does “black box rny~ticisrn.”’~

NOTES

Quoted in P. C. W. Davies and J. R. Brown, eds. The Ghost i n the Atom (Cambridge: Cambridge University Press, 1986), 113-114.

For example, theoretical physicist D’Espagnat comments: “In a re- alistic conception with no hidden variables, the wave function must be considered to be universal reality. How could we accept tha t it is ‘col- lapsed’ only by the nervous systems of some species of animals, which exist only on one or a few celestial bodies such as our Earth? Thus, once engaged along these lines, we are led to generalize the hypothesis and to take the idea of a consciousness abiding in things seriously.” See D’Espagnat, In Search of Reality (New York: Springer-Verlag, 1983), 118. More recently, Euan Squires has suggested tha t we might get around some of the thorny aspects of the measurement problem (discussed below) by suggesting that, “ ... quantum theory leads to the idea that conscious mind is one thing, i.e., tha t there is a universal consciousness.” (Squires, E. J . , “Quantum Theory and the Relation Between the Con- scious Mind and the Physical World,” Synthese 97 [1993]: 118)

‘j This is essentially the axiomatization of elementary quantum mechanics to be found in von Neumann, J., The Mathematical Foundations of Quantum Mechanics (Princeton: Princeton University Press, 1955).

I assume that since the cat is apparently incapable of collapsing its own wavepacket, we have something like a Cartesian view of animals implicit in the statement of the problem.

For example, Bohm, D., Quantum Theory (New York: Dover, 1989),

See von Neumann, Mathematical Foundations, Ch. 4. I t is now known that this proof is not conclusive-for a discussion of the historical details, consult Jammer, M., The Philosophy of Quantum Mechanics (New York: Wiley, 1974), Ch. 7. Even so, other “no hidden variables” proofs have been forthcoming which rest on less contentious assump- tions. I t is now generally agreed tha t quantum mechanics cannot be given a hidden variables interpretation. It is a consequence of Bell’s Theorem (1964; 1987) that hidden variables interpretations of quantum mechanics come at the expense of relativistically unacceptable action-at- a-distance. What is much less clear is what picture quantum mechanics paints of the world (if any), if one grants that the No Hidden Variables proofs are conclusive. For then, since quantum states must be complete descriptions of physical systems, the theorist is confronted with the possibility that a particle in a definite eigenstate of momentum will take no value whatsoever for position-it literally will not have a definite loca- tion in the spacetime continuum. By comparison, worries about the intervention of consciousness in physical processes seem to be mere trifles!

Classical mechanics is very different from quantum mechanics in this regard. For any classical mechanical system S, if {q, ..., An, ... I are the classical mechanical observables associated with tha t system, then

584-586.

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each classical mechanical state 1 of the system can be viewed as a list <a,, ..., an, ... > of exact real values for those observables. This is what is meant by the claim that classical mechanical systems exhibit “determinateness.” In classical mechanics, that value a system takes for a given observable Ai is fixed by the classical mechanical state of the system, and not by acts of observation by conscious observers.

This would have to be in the spirit, rather than the letter of von Neumann, since he was apparently committed to dualism.

Ran Lahav and I formulate a n emergentist hypothesis, and ex- plore its consequences in the context of the quantum mechanics of consciousness, in “How to be a Scientifically Respectable Property Dualist,” Journal of Mind and Behavior 13, no. 3 (1992): 211-232.

lo I t is possible that some of these neuroanatomical properties may be reducible to (non-quantum mechanical) chemical properties. I t is the next step in the reductive process tha t seems to be problematic. If the basic facts are irreducible chemical facts-“chemicalism”-the reductive physicalist will still not have won the day. For reasons to be discussed in the next section, however, there are grounds for believing that it is false that all biological facts about evolved entities can be reduced to facts about physics or chemistry.

See Kim, J., ”Psychophysical Supervenience,” Philosophical Stud- ies 41 (1982): 51-70.

See Lahav and Shanks, “How to be a Scientifically Respectable Property Dualist.”

As J. S. Bell put it in his famous paper on the EPR paradox, commenting on Bohm’s hidden variables theory:

l1

l3

. .. a hidden variable interpretation of elementary quantum theory has been explicitly constructed. That particular interpretation has indeed a grossly non-local structure. This is characteristic, according to the result to be proved here, of any such theory which reproduces exactly the quantum mechanical predictions. (Bell 1964; 1987, 14)

l4 In addition to many helpful comments from the anonymous ref- eree, I would like to thank Professor George Gale, Department of Phi- losophy at the University of Missouri-Kansas City; Professor Alex Neill, Department of Philosophy at Trinity University; Professor Ran Lahav, Department of Philosophy at The University of Haifa; Professor David Sharp, Department of Philosophy at the University of Alberta, and the members of the Philosophy Department at East Tennessee State Uni- versity-especially Hugh LaFollette-for many helpful comments and suggestions.

REFERENCES

Bell, J. S. 1964; 1987. On the Einstein-Podolsky-Rosen paradox. In Speakable and Unspeakable in Quantum Mechanics. Cambridge: Cambridge University Press.

Bohm, D. 1989. Quantum Theory. New York: Dover. Davies, P. C. W. and Brown, J. R., eds. 1986. The Ghost in the Atom.

DEspagnat, B. 1983. In Search of Reality. New York: Springer-Verlag. Field, H. 1980. Tarski’s theory of truth. In Reference, Duth and Reality,

Cambridge: Cambridge University Press.

ed. M. Platts. London: Routledge and Kegan Paul.

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Jammer, M. 1974. The Philosophy of Quantum Mechanics. New York:

Kim, J. 1982. Psychophysical supervenience. Philosophical Studies 41 :

Lahav, R. and Shanks, N. 1992. How to be a scientifically respectable

Mayr, E. 1988. Toward a New Philosophy of Biology. Cambridge:

Squires, E. J. 1993. Quantum theory and the relation between the con-

von Neumann, J. 1955. The Mathematical Foundations of Quantum Me-

Wigner, E. P. 1962. Remarks on the mind-body question. In The Scien-

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