01 January 2011

Neither necessary nor plausible

1 January, one year closer to 2012 when - if we're to believe Ervin Laszlo and other Mayan Calendar Endism fans - things either come to a very messy end or we (cue the quantum mystics' deux ex machina) somehow experience a "shift" in "global consciousness".

The latter is associated by Laszlo with brains - presumably the brains of the like-minded who enjoy a repackaging of Rudolf Steiner and Madame Blavatsky - becoming "quantum wave transceivers". One might wonder why transceivers are necessary, given that Laszlo's associates are big on precognition, two-way conversations with the dead (using valve radios or otherwise), dowsing, astrology, remote healing, telekinesis, Edgar Cayce's Ashashic Records and other delights that are not recognised in Australian law (or in hard science), but that's apparently the way it is.

In past posts on this blog I have questioned the absence of definitive scientific data substantiating the funnier assertions by exponents of quantum mysticism and suggested that nonsense on occasion harms people, not least through diversion of effort from changes that underpin the tangible improvement of human rights. A contact has now kindly pointed me to 'Is the Brain a Quantum Computer?' by Abninder Litt, Chris Eliasmith, Frederick Kroon, Steven Weinstein & Paul Thagard in 30 Cognitive Science (2006) 593–603.

They appear to be of the view that characterisation of the brain as a quantum computer is neither necessary nor plausible.
We argue that computation via quantum mechanical processes is irrelevant to explaining how brains produce thought, contrary to the ongoing speculations of many theorists. First, quantum effects do not have the temporal properties required for neural information processing. Second, there are substantial physical obstacles to any organic instantiation of quantum computation. Third, there is no psychological evidence that such mental phenomena as consciousness and mathematical thinking require explanation via quantum theory. We conclude that understanding brain function is unlikely to require quantum computation or similar mechanisms.
More pointedly, they comment that if the human brain is a quantum computer we should, if that characterisation is accepted, assume that other entities have the same consciousness. My contact noted that in questioning an article in Laszlo's World Futures journal I'd asked if acceptance of particular claims - legitimated through citation of fans of Uri Geller and other quackery - invoked acceptance of human rights for carrots and coffee cups. Litt, Eliasmith et al appear to be similarly troubled by the fuzziness of claims about the quantum brain, commenting -
Some have argued that tiny protein structures within neurons, microtubules, offer a milieu suitably sized and isolated for quantum coherence and computation (eg Hameroff 1998b; Kak 1999; Nanopoulos 1995). But these theories lack any empirical support and also run afoul of the previously mentioned decoherence–neural spike timescale discrepancies. Moreover, they raise the question of what makes brain microtubules so special that they alone allow for quantum computation. Microtubules are generic cellular structures that are involved in internal transport, combine to form cilia and flagella, and play a proven role in maintaining cytoskeletal structure (Grush & P S Churchland 1995). Found throughout the plant and animal kingdoms, their distribution in neurons is wholly unexceptional. Indeed, the hypotheses regarding microtubules offer nothing equivalent to traditional neuroscientific explanations of interspecies disparity. ... quantum–microtubule theorists have yet to outline plausible mechanisms by which species differ in their abilities. In this absence, are we to believe that carrots and rutabagas also exhibit quantum computation, or are conscious? As P S Churchland (1998) argued, "The want of directly relevant data is frustrating enough, but the explanatory vacuum is catastrophic. Pixie dust in the synapses is about as explanatorily powerful as quantum coherence in the microtubules" (p 121).
They comment that -
explaining brain function by appeal to quantum mechanics is akin to explaining bird flight by appeal to atomic bonding characteristics. The structures of all bird wings do involve atomic bonding properties that are correlated with the kinds of materials in bird wings: most wing feathers are made of keratin, which has specific bonding properties. Nevertheless, everything we might want to explain about wing function can be stated independently of this atomic structure. Geometry, stiffness, and strength are much more relevant to the explanatory target of flight, even though atomic bonding properties may give rise to specific geometric and tensile properties. Explaining how birds fly simply does not require specifying how atoms bond in feathers.

The primary aim of the cognitive sciences is to provide explanations of important mental functions, including perception, memory, language, inference, and learning. We contend that quantum properties are irrelevant to explaining brain functions, just as bonding properties are irrelevant to explaining wing function. ...

[W]e have provided an interlocking set of computational, biological, and psychological arguments against the hypothesis that the brain is a quantum computer. Let us return once more to our bird-flight analogy. The relevance of atomic bonding properties to the structure of wings does not necessitate their involvement in explaining flight, because aerodynamic mechanisms have proven sufficiently powerful to explain the phenomenon. Only if specific, flight-relevant geometric or tensile features arose purely from atomic bonding properties in feathers would it make sense to import these details into our explanations of bird flight. Because no such special properties are found in existing examples of wings, atomic bonding is not relevant to explaining bird flight. Similarly, there appear to be no special quantum mechanical properties needed to explain psychological and neurological phenomena. The onus is on those who would appeal to quantum theory to show the existence of aspects of the brain that are not explained by neurocomputational theories, and that can be explained by quantum computation or associated mechanisms. Although the discovery of solid evidence for fundamentally quantum characteristics of mental phenomena would be tremendously exciting, current ideas fall well short of this standard.