dorsal/arxiv
View SchemaQuantum Computation in Brain Microtubules? Decoherence and Biological Feasibility
| Authors | S. Hagan, S. R. Hameroff, J. A. Tuszyński |
|---|---|
| Categories | |
| ArXiv ID | quant-ph/0005025 |
| URL | https://arxiv.org/abs/quant-ph/0005025 |
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.
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"abstract": "The Penrose-Hameroff (`Orch OR\u0027) model of quantum computation in brain\nmicrotubules has been criticized as regards the issue of environmental\ndecoherence. A recent report by Tegmark finds that microtubules can maintain\nquantum coherence for only $10^{-13}$ s, far too short to be\nneurophysiologically relevant. Here, we critically examine the assumptions\nbehind Tegmark\u0027s calculation and find that: 1) Tegmark\u0027s commentary is not\naimed at an existing model in the literature but rather at a hybrid that\nreplaces the superposed protein conformations of the `Orch OR\u0027 theory with a\nsoliton in superposition along the microtubule, 2) Tegmark predicts decreasing\ndecoherence times at lower temperature, in direct contradiction of the observed\nbehavior of quantum states, 3) recalculation after correcting Tegmark\u0027s\nequation for differences between his model and the `Orch OR\u0027 model\n(superposition separation, charge vs. dipole, dielectric constant) lengthens\nthe decoherence time to $10^{-5} - 10^{-4}$ s and invalidates a critical\nassumption of Tegmark\u0027s derivation, 4) incoherent metabolic energy supplied to\nthe collective dynamics ordering water in the vicinity of microtubules at a\nrate exceeding that of decoherence can counter decoherence effects (in the same\nway that lasers avoid decoherence at room temperature), and 5) phases of actin\ngelation may enhance the ordering of water around microtubule bundles, further\nincreasing the decoherence-free zone by an order of magnitude and the\ndecoherence time to $10^{-2} - 10^{-1}$ s. These revisions bring microtubule\ndecoherence into a regime in which quantum gravity can interact with\nneurophysiology.",
"arxiv_id": "quant-ph/0005025",
"authors": [
"S. Hagan",
"S. R. Hameroff",
"J. A. Tuszy\u0144ski"
],
"categories": [
"quant-ph"
],
"title": "Quantum Computation in Brain Microtubules? Decoherence and Biological Feasibility",
"url": "https://arxiv.org/abs/quant-ph/0005025"
},
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