In the most recent issue of Nature (March 30) Christof Koch and Klaus Hepp offer a critique of theories, such as Roger Penrose and Stuart Hameroff's, that human consciousness invoke quantum principles. Most interestingly, they suggest a new thought experiment:
We challenge those who call upon consciousness to carry the burden of the measurement process in quantum mechanics with the following thought experiment. Visual psychology has caught up with magicians and has devised numerous techniques for making things disappear. For instance, if one eye of a subject receives a stream of highly salient images, a constant image projected into the other eye is only seen infrequently. Such perceptual suppression can be exploited to study whether onsciousness is strictly necessary to the collapse of the wave function. Say an observer is looking at a superimposed quantum system, such as Schrödinger’s box with the live and dead cat, with one eye while his other eye sees a succession of faces. Under the appropriate circumstances, the subject is only conscious of the rapidly changing faces, while the cat in the box remains invisible to him. What happens to the cat? The conventional prediction would be that as soon as the photons from this quantum system encounter a classical object, such as the retina of the observer, quantum superposition is lost and the cat is either dead or alive.This is true no matter whether the observer consciously saw the cat in the box or not. If, however, consciousness is truly necessary to resolve the measurement problem, the animal’s fate would remain undecided until that point in time when the cat in the box becomes perceptually dominant to the observer. This seems unlikely but could, at least in principle, be empirically verified. The empirical demonstration of slowly decoherent and controllable quantum bits in neurons connected by electrical or chemical synapses, or the discovery of an efficient quantum algorithm for computations performed by the brain, would do much to bring these speculations from the ‘far-out’ to the mere ‘very unlikely’. Until such progress has been made, there is little reason to appeal to quantum mechanics to explain higher brain functions, including consciousness.
The end of quantum theories of consciousness? Well, I suspect a rebuttal from Hamroff is forthcoming!
Reference
Koch, C. & Hepp, K. (2006): Quantum mechanisms in the brain. Nature 440: 611-612.
- Martin
Quantum Mechanics in the Brain
Henry P. Stapp
Lawrence Berkeley National Laboratory
University of California
Berkeley, California 94720, USA
Christof Koch and Klaus Hepp, in a recent article in this journal1, issued a challenge to “those who call upon consciousness to carry the burden of the measurement problem in quantum mechanics.” Lest absence of a response be construed as admission of a failure of the idea that consciousness can play, via quantum measurement effects, a crucial role in neurodynamics, or that this idea has been in any rational way damaged by the arguments put forth in the cited article, I respond here to that challenge.
Let it first be noted that the rational arguments put forth in the cited article against the idea that quantum effects can affect brain dynamics importantly at a macroscopic level rest entirely on the expectation that quantum superposition effects will be severely damped out over all but very short distances. Certainly, any effect that requires quantum coherence effects to extend over much more than molecular distances is expected to be small. However, there can be important residual macroscopic quantum effects that are not suppressed by environmental decoherence. The prime example is the quantum Zeno effect2, which can in principle give rise to macroscopic quantum effects that are immune to suppression by environmental damping. This is a key point. Because it is not well known, I give here a very simple proof.
The effects of environmentally induced decoherence are most conveniently expressed in terms of the density matrix D. The classic paper of Joos and Zeh3 shows that the effect upon a system of its interaction with its environment is generally to damp out rapidly the off-diagonal elements of its coordinate-space density matrix D.
The quantum Zeno effect is a consequence of repeatedly posing, in sufficiently rapid succession, the same measurement question. In the case of a question with a ‘Yes’ or ‘No’ answer, the outcome ‘Yes’ will be associated with a particular (projection) operator P, satisfying PP=P, and the act of posing the question—von Neumann’s famous Process1— will then be represented by replacing D by PDP + (1-P)D(1-P). If the answer to the question is ‘Yes’, the density matrix is reduced to PDP/Trace PDP. Then the fundamental interpretive rule of quantum mechanics (See von Neumann4) asserts that the probability that the outcome of the succeeding measurement question will be ‘No’ is
Trace (1-P) exp –iHt PDP exp iHt (1-P)/Trace PDP. Here H is the Hamiltonian and t is the time difference between the two measurements. Introducing for small t the power series expansion of the exponentials, and using (1-P)P=P(1-P)=0, one finds that the term lowest order in t is of order t squared. This implies that as the timing of the questions becomes rapid, on the scale of the important time scales in PDP, the evolution of the system to states where the property specified by P fails to hold will become increasingly suppressed. The decoherence term in the master equation does not affect this conclusion.
In this neural context the operator P separates out from conflicting brain activities the neural correlate of a conscious idea or intention: the action of P singles out the pattern of neurological activity associated with the thought. Hence, according to Koch and Hepp, the operator P must act over a macroscopic portion of the brain. The timings of the repetitious acts of measurement are not specified by any known laws: according to orthodox quantum ideas, the choices of both the measurement acts, and their timings, are, in Bohr’s words, “free choices” on the part of the human actor: they are constrained by no known law.
This quantum Zeno effect can provide a physics-based causal explanation of the claim of William James5 that
No object can catch our attention except by the neural machinery. But the amount of the attention which an object receives after it has caught our attention is another question. It often takes effort to keep the mind upon it. We feel that we can make more or less of the effort as we choose. If this feeling be not deceptive, if our effort be a spiritual force, and an indeterminate one, then of course it contributes coequally with the cerebral conditions to the result. Though it introduce no new idea, it will deepen and prolong the stay in consciousness of innumerable ideas which else would fade more quickly away.
Everywhere, then, the function of effort is the same: to keep affirming and adopting the thought which, if left to itself, would slip away.
The quantum Zeno holding action occurs even if D is very nearly diagonal: the form of D does not enter into the proof or the result. Numerous empirical ramifications of this theoretically possible physics-based effect have been described in Schwartz, Stapp, and Beauregard.6
The challenge posed by Koch and Hepp refers to an experiment in which a subject views with one eye a stream of highly salient images, which will capture his conscious attention most of the time, and views with the other eye photons that determine which of two initially superposed quantum states a certain system will be observed to be in. According to the no-reduction-without-a-discriminating-conscious-thought hypothesis the two parallel components of the quantum system will remain superposed until a discriminating conscious experience occurs. This hypothesis is to be contrasted with the common-sense idea that the reduction occurs when the first discriminating macroscopic event occurs. In the words of Heisenberg7 the transition “takes place as soon as the interaction of the object with the measuring device, and thereby with the rest of the world, has come into play”. At that point in time all information concerning the quantum phase relationships between the two different parallel components is lost irretrievably into “the rest of the world”, and there is no way to discriminate empirically between the possibility (1) that the collapse occurs at this point in time, and the possibility (2) that the reduction will not occur until some discriminating conscious event occurs. This lack of determinability between (1) and (2) follows from the fact that the density matrices for the system—excluding the “rest of the world”—are identical in the two scenarios (1) and (2), and, according to the orthodox rules, all predictions about any system is derivable from its density matrix.
The idea that no reduction occurs until consciousness intervenes may seem ridiculous. Still, earlier reductions cannot occur without violating the basic known dynamical law, the Schroedinger equation, and there appears to be no reason for that law to fail if we consider only the physical universe alone. No experiment has ever established any credible evidence that reductions occur in physical systems, however large or small, when left to themselves. And quantum mechanics gives no predictions about observed dynamical phenomena without bringing in the intervention by “the observer” that is called “Process 1” by von Neumann, and a “ free choice on the part of the experimenter” by Bohr. There is no a priori reason why realities such as our conscious experiences should not be causally efficacious, and there are powerful evolutionary reasons why they should be efficacious. In view of the acknowledged “weirdness” of quantum phenomena, the method of science counsels a search for a rational understanding that fits all the empirical facts, and explains them, rather than adherence to prevailing intuitions.
The Koch-Hepp experiment is not described in detail. Many variations are possible, and they cannot all be discussed here. But one may suppose that detectors of the pertinent retinal activities are installed, and are connected to timers that record, for later examination by the scientists who are conducting the experiment, the times of the pertinent retinal responses. In the common sense scenario (1) the reduction occurs when some part of the retina responds. This reduction fixes the readings on a timer that will tell the scientists which of the two superposed components is actualized, and when that retinal event happened. In scenario (2) the reduction usually does not occur until a scientist observes the timers. The observed readings fix the time—in the past—when the retinal event occurred on that branch of potentiality that was actualized later by the reduction event associated with the scientist’s conscious experience. However, if the subject happens to experience a discriminating event—before the scientist does—then the reduction event associated with his (the subject’s) experience will select from the previously superposed quantum potentialities the branch containing the associated pertinent retinal activity, and, with it, the timer setting that identifies the (earlier) time at which that retinal event occurred. But there is nothing in the realm of experience that discriminates between scenario’s (1) and (2). Similar situations were discussed in a recent analysis (Stapp7) of a famous experiment performed by Benjamin Libet, and an even more famous experiment discussed by Einstein, Podolsky, and Rosen.
Consciousness may indeed be a “placeholder”, as Koch and Hepp suggest. But for what is it holding a place, if not for consciousness itself? As a real aspect of nature with which we have direct experience, should not consciousness have a necessary place in our theories of nature, and one that allows it to play a causally efficacious role?
References
1. Koch, C. & Hepp, K. Quantum Mechanics in the Brain. Nature 440, 611-612 (2006).
2. Misra, B. & Sudarshan, E. The Zeno’s Paradox in Quantum Theory. J. Math. Phys. 18, 756-763 (1977).
3. Joos, E. & Zeh, H. The Emergence of Classical Properties Through Interaction with the Evironment. Z. Phys. B59, 223-243 (1985).
4. Von Neumann, J. Mathematical Foundations of Quantum Mechanics (Princeton University Press, Princeton, 1955).
5. James, W. Psychology: The Briefer Course in William James: Writings 1879-1899. pp.227, 421. (New Library of America, New York, 1992)
6. Schwartz, J., Stapp, H. and Beauregard, M. Quantum Theory in Neuroscience and Psychology: a Neurophysical Model of the Mind-Brain Interaction. Phil Trans. Royal Society B360, 1309-1327 (2005).
7. Heisenberg, W. Physics and Philosophy. p. 54 (Harper, New York, 1958).
8. Stapp, H. Quantum Interactive Dualism: The Libet and Einstein-Podolsky-Rosen Causal Anomalies. Lawrence Berkeley National Laboratory Report LBNL-59906.
(http://www-library.lbl.gov/docs/LBNL/599/06/PDF/LBNL-59906.pdf)
To be published in Erkenntnis (2006)
Acknowledgement. This work was supported by the Director, Office of Science, Office of High energy and Nuclear Physics, of the U.S. Department of Energy under contract DE-AC02-05CH11231.
HOW TO CONNECT (QUANTUM) PHYSICS WITH HUMAN (UN)CONSCIOUS INFORMATION PROCESSING? RESPONSE TO KOCH AND HEPP
Maurits van den Noort and Peggy Bosch
University of Bergen, Norway
With great interest we read the essay in Nature by Christof Koch and Klaus Hepp on quantum mechanics in the brain (1). We agree with them that all biological organisms must somehow obey the laws of both classical- and quantum physics, and that the relation between quantum mechanics and higher brain functions is far from understood (2).
In line with Koch and Hepp, we also think that human conscious information processing seems to follow the laws of classical physics. However, in our opinion, Koch and Hepp are a bit too simplistic in the way they dismiss the possible connection and underlying mechanisms between quantum mechanics and (human) unconscious information processing. From their essay we get the impression that neuroscience has solved all mysteries and that all is known about human information processing. Unfortunately, that is not the reality yet (3-5). Moreover, Koch and Hepp use quantum computers as additional evidence for their negative statement on the link between quantum physics and human information processing; however, this technology is still being developed and its exact limitations are unknown yet (6).
Of course, we totally agree with Koch and Hepp (1) that more is needed than wild theoretical speculations. In addition, it is true that neuroscientists nowadays can use advanced neuroimaging techniques to investigate conscious and unconscious information processing in the human brain and that these advanced techniques must be used to support a theoretical theory with experimental evidence (7, 8). We are of the opinion that the current theories on the relation between quantum mechanics and human information processing (9, 10) offer a ground on which further theoretical- and experimental research could build. Note that the scientific debate between Albert Einstein (11, 12) and Niels Bohr (13) on the principles of quantum physics also resulted in huge scientific progress.
To conclude, the critical essay written by Koch (14) and Hepp, who are two leading scientists, is extremely useful since they emphasis the importance of experimental evidence and we totally agree with them on that. However, in our opinion, they are a bit too negative about the future outcomes of the research on quantum mechanics in the brain. Anyway, perhaps their criticism (like the Einstein-Bohr debate in the last century (11-13)) could be a challenge for other scientists and a reason to closely collaborate (15) on one of the major remaining problems in science, namely; how to solve the measurement problem in quantum physics (16)?
1) Koch, C., Hepp, K. Quantum mechanics in the brain. Nature 440, 611 (2006).
2) Van den Noort, M. W. M. L. The Unconscious Brain: The Relative Time and Information Theory of Emotions. Oegstgeest, the Netherlands: Citadel (2003).
3) Fields, R. D. Beyond the Neuron Doctrine. Scientific American Mind 17(3), 21-27 (2006).
4) Van den Noort, M. W. M. L., Bosch, M. P. C. Brain Cell Chatter. Scientific American Mind 17(5), 4-5 (2006).
5) Fields, R. D. Beyond the Neuron Doctrine: Fields Replies. Scientific American Mind 17(5), 5 (2006).
6) Childress, L., Gurudev Dutt, M. V., Taylor, J. M., Zibrov, A. S., Jelezko, F., Wrachtrup, J., Hemmer, P. R., Lukin, M. D. Coherent Dynamics of Coupled Electron and Nuclear Spin Qubits in Diamond. Science 314, 281-285 (2006).
7) Van den Noort, M. W. M. L. Unconscious information processing of emotions: Non-linear processing. NeuroImage 22(S1), 27 (2004).
8) Van den Noort, M. W. M. L., Bosch, M. P. C., Hugdahl, K. Understanding the unconscious brain: An ERP-study on emotions. NeuroImage 26(S1), 28 (2005).
9) Hameroff, S. R. Quantum Computation In Brain Microtubules? The Penrose-Hameroff “Orch OR” model of consciousness. Philosophical Transactions Royal Society London (A) 356, 1869-1896 (1998).
10) Schwartz, J., Stapp, H., Beauregard, M. Quantum Theory in Neuroscience and Psychology: A Neurophysical Model of the Mind-Brain Interaction. Philosophical Transactions of the Royal Society of London (B) 360, 1309-1327 (2005).
11) Einstein, A. “Autobiographical Notes” in Albert Einstein: Philosopher-Scientist. In: P. A. Schilpp (Ed.), Albert Einstein: Philosopher-scientist (pp. 1-94). La Salle, IL: Open Court (1949).
12) Einstein, A. “Remarks Concerning the Essays Brought Together in This Cooperative Volume”. In: P. A. Schilpp (Ed.), Albert Einstein: Philosopher-scientist (pp. 665-688). La Salle, IL: Open Court (1949).
13) Bohr, N. “Discussion with Einstein on epistemological problems in atomic physics”. In: P. A. Schilpp (Ed.), Albert Einstein: Philosopher-scientist (pp. 201-241). La Salle, IL: Open Court (1949).
14) Koch, C., Preuschoff, K. Betting the house on consciousness. Nature Neuroscience 10(2), 140-141 (2007).
15) Koch, C., Crick, F. The problem of consciousness. Scientific American 12(1), 10-17 (2002).
16) Penrose, R. A theory of everything? Nature 433, 259 (2005).
I havent read the other responses so I apologise if this has not already been mentioned; but the thought experiement above is invalid if testing for “consciousness collapses the wave”.
First of all the experiment automatically assumes that any communication or impact which an observers consciousness would have on a quantum state, *must* be conducted via photons in relatvistic mode.
If “consciouness” acts as a causal mechanism in order to define values of quantum states, then it is likely a non-local entanglement type dynamic, and certainly not conducted through photons.
If an obsever causes superposition collpase it is happening instantly if not slightly faster. Hence photons are a red herring.
Of course you could do this experiement but it would prove nothing, other than perhaps blind the eye of the poor volunteer
[...] Koch on (= against) quantum consciousness theory [...]
Are there any resources out there for psychology undergrads who are interested in the subject of quantum consciousness?