Quantum Chaos in Biology


by wuliheron
Tags: biology, chaos, quantum
wuliheron
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Mar7-12, 02:35 PM
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http://www.technologyreview.com/blog...7628/?p1=blogs

For those who might not know of the theory the goal of quantum chaos theory is to explain all of classical physics including classical chaos as emerging from quantum systems. They've had some experimental success in the past, but this new paper has profound implications if confirmed. However, the exact philosophical foundations of the theory are a mystery to me so I thought it might be a good subject to explore here.

Correct me if I'm wrong, but the theory appears to be another contextual one. It proposes no metaphysics and makes no claims about Indeterminacy and merely attempts to describe quanta contextually. However, I'm a bit confused about how the theory proposes classical chaos emerges from quantum systems.
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apeiron
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Mar7-12, 04:17 PM
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Quote Quote by wuliheron View Post
http://www.technologyreview.com/blog...7628/?p1=blogs

For those who might not know of the theory the goal of quantum chaos theory is to explain all of classical physics including classical chaos as emerging from quantum systems. They've had some experimental success in the past, but this new paper has profound implications if confirmed. However, the exact philosophical foundations of the theory are a mystery to me so I thought it might be a good subject to explore here.

Correct me if I'm wrong, but the theory appears to be another contextual one. It proposes no metaphysics and makes no claims about Indeterminacy and merely attempts to describe quanta contextually. However, I'm a bit confused about how the theory proposes classical chaos emerges from quantum systems.
What the article is speculating about is a critical point behaviour that biological systems might harness. The "ordinary" view is that the transition from QM to classical behaviour would be a swift one due to thermal decoherence. The "chaotic" view is that you could use the right kind of biomolecular scaffolding to hold the decoherence poised at the critical point and so trap it and milk more more out of it in some fashion - as in light gathering during photosynthesis.

However chaos seems entirely the wrong term to describe critical points. Criticality is better.

Criticality is the exact point where things change, but have not yet changed. In the classical realm, as with the transitions of water, you physically get a mixed phase, and an easily reversible one. So as with critical opalescence, you get liquid and vapor over all scales, and the two states fluctuating back and forth over all these scales.

People have described this poised state as the edge of chaos, rather than chaos. And the whole point is its instability.

So perhaps the philosophical issue is how far can the classical analogy be stretched? Are we talking of "quantum chaos" as a physical mix of quantum and classical states? Are we claiming a reversible equilbrium where decoherence and recoherence is going on over all scales?

It is an interesting possibility that there may be a transition zone and decoherence can be trapped - perhaps along the lines of the quantum zeno effect. But this is something else than the standard quantum chaos debate in my view.

There, the philosophical question is to do with the uncertainty involved in measuring initial conditions. Is the planck scale cut-off an issue for the determinism that is presumed by deterministic chaos models? You can't seem to get deterministic sensitivity to initial conditions if initial conditions are ontologically indeterminate. (But then a decoherence view of QM may allow you to get at least a reliable average when it comes to the concept of initial conditions, a basis that is determinate enough to underpin the classical model).
apeiron
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Mar8-12, 06:08 AM
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Quote Quote by apeiron View Post
Are we talking of "quantum chaos" as a physical mix of quantum and classical states? Are we claiming a reversible equilbrium where decoherence and recoherence is going on over all scales?
OK, had a chance to read the paper itself - http://arxiv.org/pdf/1202.6433v1.pdf - and realised it is that Stu Kauffman.

And yes, he is indeed claiming reversibility between quantum and classical states. What he calls his poised realm.

So he suggests, for example, that a chromophore is designed so that the decohering effect of the thermal cellular jostle is nicely balanced against a re-cohering effect of further arriving photons to produce an extended fractal quantum-classical mixture.

However the more standard view of what is going on in quantum biology is that with the right kind of molecular guide structures, the thermal noise is not enough to collapse the coherence and instead just nudges it intact in the right direction. Still a tricky operation, but no novelties like re-coherence and critical point behaviour.

See http://www.nature.com/news/2011/1106...l/474272a.html

Now Kauffman is a brilliant modeller, but also a little wild IMO. And with this Whiteheadian poised realm theory, he is not only positing this rather whacky sounding recoherence thing, but is also claiming that it is the secret of consciousness.

I will advance the working hypothesis that this "Poised Realm" in the human and probably other brains, IS consciousness.

http://stuartkauffman.com/index_25_1612352741.pdf
As for quantum chaos of the conventional kind, that is still about the conflict between the QM and deterministic chaos descriptions of the same system....

Chaos is problematic because the way a quantum wave develops in time is determined by the associated energy levels. A mathematical consequence of the existence of energy levels is that quantum timedevelopment contains only periodic motions with definite frequencies – the opposite of chaos. Therefore there is no chaos in quantum mechanics, only regularity. How then, can there be chaos in the world?

http://www.physics.bristol.ac.uk/peo...s/Berry358.pdf
Though Berry also thinks the answer is simple....

The true reason for the prevalence of chaos is that large quantum systems are hard to isolate from from their surroundings. Even the ‘patter of photons’ from the Sun (whose re-emission gives the light by which we see Hyperion) destroys the delicate interference underlying the quantum regularity. This effect, of large quantum systems being dramatically sensitive to uncontrolled external influences, is called decoherence. In the classical limit, the quantum suppression of chaos is itself suppressed by decoherence, allowing chaos to re-emerge as a familiar feature of the largescale world.


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