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Quantum Computation in Brain Microtubules? Decoherence and Biological
Feasibility
S. Hagan, S. R. Hameroff, J. A. Tuszyński
abstract: The Penrose-Hameroff (`Orch OR') model of quantum computation in brain
microtubules has been criticized as regards the issue of environmental
decoherence. A recent report by Tegmark finds that microtubules can maintain
quantum coherence for only $10^{-13}$ s, far too short to be
neurophysiologically relevant. Here, we critically examine the assumptions
behind Tegmark's calculation and find that: 1) Tegmark's commentary is not
aimed at an existing model in the literature but rather at a hybrid that
replaces the superposed protein conformations of the `Orch OR' theory with a
soliton in superposition along the microtubule, 2) Tegmark predicts decreasing
decoherence times at lower temperature, in direct contradiction of the observed
behavior of quantum states, 3) recalculation after correcting Tegmark's
equation for differences between his model and the `Orch OR' model
(superposition separation, charge vs. dipole, dielectric constant) lengthens
the decoherence time to $10^{-5} - 10^{-4}$ s and invalidates a critical
assumption of Tegmark's derivation, 4) incoherent metabolic energy supplied to
the collective dynamics ordering water in the vicinity of microtubules at a
rate exceeding that of decoherence can counter decoherence effects (in the same
way that lasers avoid decoherence at room temperature), and 5) phases of actin
gelation may enhance the ordering of water around microtubule bundles, further
increasing the decoherence-free zone by an order of magnitude and the
decoherence time to $10^{-2} - 10^{-1}$ s. These revisions bring microtubule
decoherence into a regime in which quantum gravity can interact with
neurophysiology.
- oai_identifier:
- oai:arXiv.org:quant-ph/0005025
- categories:
- quant-ph
- comments:
- 10 pages
- arxiv_id:
- quant-ph/0005025
- created:
- 2000-05-04
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