[ExI] Fwd: "The Quantum Mind"
citta437 at aol.com
citta437 at aol.com
Fri Dec 21 22:53:42 UTC 2007
" Cold Numbers Unmake the Quantum Mind
Calculations show that collapsing wave functions in the scaffolding
of the brain can't explain the mystery of consciousness. Sir Roger
Penrose is incoherent, and Max Tegmark says he can prove it. According
to Tegmark's calculations, the neurons in Penrose's brain are too warm
to be performing quantum computations--a key requirement for Penrose's
favorite theory of consciousness.
Penrose, the Oxford mathematician famous for his work on tiling the
plane with various shapes, is one of a handful of scientists who
believe that the ephemeral nature of consciousness suggests a quantum
process. In the realm of the extremely small, an object with a property
such as polarization or spin may exist in any of a number of quantum
states. Or, bizarrely, it may inhabit several quantum states at once, a
property called superposition. A quantum superposition is extremely
fragile. If an atom in such a state interacts with its environment--by
being bumped or prodded by nearby atoms, for instance--its waveform can
"collapse," ending the superposition by forcing the atom to commit to
one of its possible states.
To some investigators, this process of coherence and collapse seems
strikingly similar to what goes on in the mind. Multiple ideas flit
around below the threshold of awareness, then somehow solidify and wind
up at the front of our consciousness. Quantum consciousness aficionados
suspect that the analogy might be more than a coincidence. Eleven years
ago, Penrose publicly joined their number, speculating in a popular
book called The Emperor's New Mind that the brain might be acting like
a quantum computer.
"Between the preconscious and conscious transition, there's no
obvious threshold," says Penrose's sometime collaborator Stuart
Hameroff, an anesthesiologist at the University of Arizona in Tucson.
Ideas start out in superposition in the preconscious and then wind up
in the conscious mind as the superposition ends and the waveform
collapses. "The collapse is where consciousness comes in," says
But what exactly is collapsing? From his studies of
neurophysiology, Hameroff knew of a possible seat for the quantum
nature: "microtubules," tiny tubes constructed out of a protein called
tubulin that make up the skeletons of our cells, including neurons.
Tubulin proteins can take at least two different shapes--extended and
contracted--so, in theory, they might be able to take both states at
once. If so, then an individual tubulin protein might affect its
neighbors' quantum states, which in turn affect their neighbors'--and
so forth, throughout the brain. In the 1990s, Penrose and Hameroff
showed how such a tubulin-based quantum messaging system could act like
a huge quantum computer that might be the seat of our conscious
The idea attracted a few physicists, some consciousness researchers,
and a large number of mystics. Quantum physicists, however, largely
ignored it as too speculative to be worth testing with numerical
calculations. Now Tegmark, a physicist at the University of
Pennsylvania, has done the numbers. In the February issue of Physical
Review E, Tegmark presents calculations showing just what a terrible
environment the brain is for quantum computation.
Combining data about the brain's temperature, the sizes of various
proposed quantum objects, and disturbances caused by such things as
nearby ions, Tegmark calculated how long microtubules and other
possible quantum computers within the brain might remain in
superposition before they decohere. His answer: The superpositions
disappear in 10-13 to 10-20 seconds. Because the fastest neurons tend
to operate on a time scale of 10-3 seconds or so, Tegmark concludes
that whatever the brain's quantum nature is, it decoheres far too
rapidly for the neurons to take advantage of it.
Do all scientists agree?
"If our neurons have anything at all to do with our thinking, if
all these electrical firings correspond in any way to our thought
patterns, we are not quantum computers," says Tegmark. The problem is
that the matter inside our skulls is warm and ever-changing on an
atomic scale, an environment that dooms any nascent quantum computation
before it can affect our thought patterns. For quantum effects to
become important, the brain would have to be a tiny fraction of a
degree above absolute zero.
Hameroff is unconvinced. "It's obvious that thermal decoherence is
going to be a problem, but I think biology has ways around it," he
says. Water molecules in the brain tissue, for instance, might keep
tubulin coherent by shielding the microtubules from their environment.
"In back-of-the-envelope calculations, I made up those 13 orders of
magnitude pretty easily."
Some members of the quantum-consciousness community, however,
concede that Tegmark has landed a body blow on Penrose-Hameroff-type
views of the brain. "Those models are severely impacted by these
results," says physicist Henry Stapp of Lawrence Berkeley National
Laboratory in California. (Stapp's own theory of quantum consciousness,
he says, is unaffected by Tegmark's arguments.)
Physicists outside the fray, such as IBM's John Smolin, say the
calculations confirm what they had suspected all along. "We're not
working with a brain that's near absolute zero. It's reasonably
unlikely that the brain evolved quantum behavior," he says. Smolin
adds: "I'm conscientiously staying away" from the debate."
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