From: Mitchell Porter (email@example.com)
Date: Mon Dec 01 2003 - 17:53:26 MST
>I'm not sure you completely got the implications of Tegmark's
>paper. His straightforward calculations make it seem extraordinarily
>unlikely that one could do quantum computation in a brain at
>biological temperatures. That, coupled with the fact that there is no
>actual evidence in favor of the quantum hypothesis at all (other than
>pure speculation) tends to lead one to disbelieve in it very
Tegmark's calculations address rather artificial situations like:
an ion is on the inside and the outside of a membrane,
another ion passes by, and the first ion's superposition is
decohered. So Tegmark certainly showed up a flaw in the
models he criticised, which did blithely talk about that sort
of superposition, without regard for the effects of
environmental decoherence. But if there is significant
quantum coherence in living matter, it's probably due to
collective, cooperative effects, akin to Bose condensation.
One old favorite in the quantum-mind literature is a Bose-like
condensation of phonons which should occur at high
temperatures ("Frohlich coherence"). Then there's more
recent work on quantum phase transitions in periodic
structures; under the right conditions, the "correlation
length" - the scale on which quantum correlations are
exhibited - can go to infinity. One might imagine that this
can happen to the electrons in a periodic structure like a
microtubule. And so on. There's a whole class of models
still waiting to be investigated.
Why take this possibility seriously? Two reasons. First,
quantum mechanics is the basic theory, and we have yet
to investigate the dynamics of entanglement in everyday
substances. I have never seen a decoherence calculation
even for something as simple as diamond. Presumably
there's a temperature-dependent finite scale on which
entanglement (between the bonding electrons, say)
might be exhibited. Probably it's negligible at anything
above absolute zero. But until someone figures out how
to do the calculation, it's hard to say for sure. And that
goes double for biological matter.
The second reason is philosophical, or phenomenological.
If you think that identifying states of consciousness with
coarse-grained mesoscopic properties of an ensemble of
decoherent microscopic systems (and that's how I would
physically characterize the states of orthodox computational
neuroscience) is a-priori implausible, then you'll be
motivated to consider the alternatives. But that's a fuzzy
judgment call over which people disagree.
>That is not the way the word is usually used. Or, at least, "reality"
>that metaphysics deals with has to do with issues like existence,
>ontology, epistemology etc. It has nothing to do with physics per se.
The ontology of physics is a highly disputed thing - see the
difference between Newton, Kant, Mach, and the later Einstein
on the nature of space, or the war of all against all in the
interpretation of quantum theory. So if even the physics of
mind is not what we think it is, the metaphysics is hardly
going to stay put.
Hot chart ringtones and polyphonics. Go to
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