Thought Provoker
Posts: 530
Joined: April 2007
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Hi All,
In response to JAM's discussions, I have been trying to understand other points of views of the general idea of the brain using quantum computations. In this effort, I ran across Walter J Freeman. Here is what the scholarpedia has to say abut him...
Walter J Freeman (b. 30 January 1927 in Washington DC) studied physics and mathematics at M.I.T., electronics in the Navy in World War II, philosophy at the University of Chicago, medicine at Yale University, internal medicine at Johns Hopkins, and neuropsychiatry at UCLA. He has taught brain science in the University of California at Berkeley since 1959, where he is Professor of the Graduate School.
I would suggest these kind of credentials would make sense as someone qualified to speak on quantum effects in the brain. While Dr. Hameroff references Dr. Freeman's research, I get the impression the Dr. Freeman is more conservative in his hypotheses than Dr. Hameroff.
Is JAM hinted at, there is support for the idea that the brain includes a quantum computer. The Standford Encyclopedia of Philosophy includes several examples of Quantum Approaches to Consciousness. Here is the entry's intro...
It is widely accepted that consciousness or, more generally, mental activity is in some way correlated to the behavior of the material brain. Since quantum theory is the most fundamental theory of matter that is currently available, it is a legitimate question to ask whether quantum theory can help us to understand consciousness. Several approaches answering this question affirmatively, proposed in recent decades, will be surveyed. It will be pointed out that they make different epistemological assumptions, refer to different neurophysiological levels of description, and use quantum theory in different ways. For each of the approaches discussed, problematic and promising features will be equally highlighted.
Here is the entry they had for the Penrose-Hameroff model...
In the scenario developed by Penrose and neurophysiologically augmented by Hameroff, quantum theory is claimed to be effective for consciousness, but this happens in an extremely sophisticated way. It is argued that elementary acts of consciousness are non-algorithmic, i.e., non-computable, and they are neurophysiologically realized as gravitation-induced reductions of coherent superposition states in microtubuli.
Unlike the approaches discussed so far, which are essentially based on (different features of) status quo quantum theory, the physical part of the scenario, proposed by Penrose, refers to future developments of quantum theory for a proper understanding of the physical process underlying quantum state reduction. The grander picture is that a full-blown theory of quantum gravity is required to ultimately understand quantum measurement (see the entry on quantum gravity).
...Penrose suggests that a valid formulation of quantum state reduction replacing (1) must faithfully describe an objective physical process that he calls objective reduction. Since present-day quantum theory does not contain such a picture, he argues that effects not currently covered by quantum theory should play a role in state reduction. Ideal candidates for him are gravitational effects since gravitation is the only fundamental interaction which is not integrated into quantum theory so far. Rather than modifying elements of the theory of gravitation (i.e., general relativity) to achieve such an integration, Penrose discusses the reverse: that novel features have to be incorporated in quantum theory for this purpose. In this way, he arrives at the proposal of gravitation-induced objective state reduction.
Why is such a version of state reduction non-computable? Initially one might think of an objective version of state reduction in terms of a stochastic process, as most current proposals for such mechanisms indeed do (see the entry on collapse theories). This would certainly be indeterministic, but probabilistic and stochastic processes can be standardly implemented on a computer, hence they are definitely computable. Penrose (1994, Secs 7.8 and 7.10) sketches some ideas concerning genuinely non-computable, not only random, features of quantum gravity. In order for them to become viable candidates for explaining the non-computability of gravitation-induced state reduction, a long way still has to be gone.
With respect to the neurophysiological implementation of Penrose's proposal, his collaboration with Hameroff has been crucial. With his background as an anaesthesiologist, Hameroff suggested to consider microtubules as an option for where reductions of quantum states can take place in an effective way, see e.g., Hameroff and Penrose (1996). The respective quantum states are assumed to be coherent superpositions of tubulin states, ultimately extending over many neurons. Their simultaneous gravitation-induced collapse is interpreted as an individual elementary act of consciousness. The proposed mechanism by which such superpositions are established includes a number of involved details that remain to be confirmed or disproven.
The idea of focusing on microtubuli is partly motivated by the argument that special locations are required to ensure that quantum states can live long enough to become reduced by gravitational influence rather than by interactions with the warm and wet environment within the brain.
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By and large, the scenario by Penrose and Hameroff represents a highly speculative approach with conceptual problems and without plausible concrete ideas for empirical confirmation. On the other hand, it is worthwhile to remember Bohr's bonmot that the question may not be whether a theory is too crazy but whether it is crazy enough.
I present this as an attempt to reaffirm JAM's suggestion the brain's reliance on quantum mechanics isn't that far-fetched considering it is receiving serious consideration. Penrose-Hameroff may be at an extreme end of the spectrum, but I offer we shouldn't discount the idea out of hand. Chances are all of these "Quantum Approaches to Consciousness" are incomplete in some manner.
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