Recycled Rant: the Quantum Mind

This is a topic which seems to come up with depressing regularity, so I figure I should put my stance on the record. The bulk of this post is recycled from a Memoirs of a Skepchick comment thread.

For various reasons, I am extremely skeptical of the notion that consciousness could be rooted in quantum phenomena. Of course, the entire world is quantum, in a sense: it’s the principles of quantum mechanics which determine the properties of materials out of which the world is made. Like Democritus of Abdera said twenty-five hundred years ago, “Nothing exists save atoms and the void”, and quantum physics constitutes the rules by which atoms play.

The challenge, then, is not to say “all is quantum” (a statement with no more content, by itself, than saying “all is love”). In what way do the strange and esoteric mathematical descriptions of the atomic and sub-atomic world build up the everyday stuff with which we are so familiar? This is a deep problem, one with many mysteries left to resolve, and physicists spend lots of time worrying about it. One thing which we do know is that when you put a lot of quantum particles together, at a certain point they stop acting in the quantum way and become better approximated by Newton’s laws of classical mechanics. This is odd, because if you put a pile of classical pieces together, you get a bigger classical object! Newton’s laws reproduce themselves at higher scales, but the quantum laws do not.

It’s a bit like discovering that all the ordinary houses on your ordinary street are made of bricks from Faerie.

So, in order to test the idea that consciousness, Mind, Spirit or any such vaguely defined phenomenon has a quantum flavor, we need to know if essential aspects of Mind depend upon objects which are small and placid enough for quantum oddities to apply. Lengths, time scales and temperatures need to be sufficiently small to avoid the problem of decoherence, the tendency of quantum objects to collapse into classical behavior.

On the one hand, we have fairly specific models of how brain cells might contain tiny switching elements to which quantum mechanics might apply. The most notable by far is Penrose and Hameroff’s proposal that “microtubules” — protein rods which form a kind of cellular skeleton, used for transporting molecules around and giving the cell mechanical rigidity — can transmit quantum pulses. Unfortunately, this model doesn’t stand up to close scrutiny very well: decoherence steps in and ruins everything. Hameroff, an anaesthesiologist, came up with a (moderately wacky) way in which this “model” explained the action of anaesthetics. Supporters made a big fooferaw about how scientists had no other model to explain aneasthetics, but oops, never tell a scientist that something can’t be explained; we now have biochemical theories which handle anaesthetics without needing to invoke quantum consciousness.

The previous hypothesis of hydrophobic action, that anesthetics interact with cell membrane lipid, has been abandoned in favor of mechanisms involving protein ion channels in the brain, particularly ligand-gated channels such as receptors for GABA, NMDA receptors, and nicotinic acetylcholine receptors (Flood, 2002). These hypotheses have substantial empirical support (e.g., Garrett & Gan, 1998; Siegwart, Krähenbühl, Lambert, & Rudolph, 2003; Williams & Akabas, 2002). As Flood stated, “Every general anesthetic in use today acts on at least one type and in some cases several types of ligand gated ion channels” (p. 153). None of the proposed explanatory mechanisms involve quantum mechanical properties or quantum computation.

The neuroscientists have also done a very good job finding places in brains where neurons can be probed directly. In the barn owl, for example, there is a brain part called the inferior colliculus, which the owl uses to process sound. We can identify places in the inferior colliculus where neurons act like AND gates: they have two inputs and only produce an output when both inputs fire simultaneously. Models exist to explain this in terms of ion fluxes through the neuron’s cell membrane (“dendritic computation” is one term, referring to the dendrites which carry the input signals). These models do not invoke quantum mechanics.

One of the better general resources I have found on this subject is a paper by Litt et al., in the journal Cognitive Science (2006). They lay out the evidence 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.

In essence, we can enclose all the quantum weirdness within “black boxes” and discuss the interaction of the boxes using classical science. There’s legitimate science in figuring out what goes on inside those black boxes, but it’s equally legitimate (and perhaps more useful) to understand what happens when they hook up together.

Indisputably, phenomena requiring quantum mechanical explanation exist throughout the brain, and are fundamental to any complete understanding of its structure and physical mechanics. […] However, none of these effects contribute essentially to explaining the overall functionality of the associated system, which can be fully described without explicit appeal to quantum-level phenomena. In our wing analogy, it is unnecessary to refer to atomic bonding properties to explain flight. We contend that information processing in the brain can similarly be described without reference to quantum theory. Mechanisms for brain function need not appeal to quantum theory for a full account of the higher level explanatory targets.

My favorite bit might be the quotation they give from P. S. Churchland, who said, “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.”

Penrose has also argued that classical computers cannot perform some of the tasks which humans do quite readily. This argument from computational complexity, however, also falls flat. Solomon Feferman dissected it fairly neatly in a review entitled “Penrose’s Gödelian Argument”; more recently, Mark C. Chu-Carroll has written relevant posts about “quantum complexity classes” at his blog Good Math, Bad Math. (The computer scientist Scott Aaronson has also advanced plausible arguments that a quantum computer can’t solve NP-complete problems in polynomial time.) It is not widely appreciated that Penrose’s hypothesis requires much more than your plain-vanilla quantum computing: in his view, the brain must be able to solve uncomputable problems. Somehow, in this view, the brain exploits subtleties in an as-yet-unknown theory of quantum gravity in order to tweak wavefunction collapse and beat the Gödel limit.

That’s quite a lot to ask for! Needing quantum mechanics is one thing, but needing a hyperquantum theory nobody has discovered yet is a less attractive proposition.

Then we have the people who claim that quantum entanglement can explain telepathy or telekinesis. Using esoteric jargon and vague pseudo-math to lend credence to a phenomenon which nobody has experimentally observed, and which experiments have quite frequently ruled out — it’s a bit like a ghost leading a blind man.

This is the realm of Deepak Chopra and the charlatans who made What the Bleep Do We Know!? To them, quantum is just a handy term, on a par with “energy field” or “Good Side of the Force”. None of the specifics of modern physics relate in any way to their specious psychobabble. There’s more good science in the Beach Boys’ song “Good Vibrations” than in Chopra’s whole catalog. They want the credibility of modern science, the trust people place in the competence of white-coated Einsteins, but they’re not willing to pay the price. They want to provide the appearance of reconciling science and faith, but what they have truly reconciled is jargon with gullibility.

7 thoughts on “Recycled Rant: the Quantum Mind”

  1. I agree with your conclusions but I have one nit to pick with your argument. Cognitive function doesn’t necessarily require subjective experience. You can imagine a program that recognizes patterns and answers questions that “require reason” as a human would but didn’t reference itself in any way. You can even imagine a computer that pursues some kind of self-interest — makes money off stock trades and sends e-mails telling people to plug it into more computers and information sources, haggles for low-priced servers — but doesn’t claim to have an internal monologue or subjective experience (especially if there’s no money in so claiming).

    I’m not trying to argue that internal monologue or subjective experience is somehow a higher order of reasoning or inexplicable, just that a specific explanation of reasoning doesn’t explain why people claim to have subjective experience. And I’m not trying to get into the question of what it means, if anything, for there to be subjective experience (hard to observe) as opposed to just critters that claim to have s.e.. I’m just saying that even if you believe s.e. is just a matter of appearance, that appearance may need to be explained separately from reasoning ability, even if that explanation isn’t very tricky.

    Anyway, I agree with your main conclusion for simple reasons that fit well with your observations on current research. Any argument that human reasoning abilities or subjective experience must rely on phenomenon X is an argument from ignorance plus ego. A sufficiently long time ago we couldn’t imagine building a machine that plays chess or observing the things we routinely see on fMRIs now. I see no reason science won’t keep knocking us down more notches in the future.

  2. Amendment: I said “Any argument that human reasoning abilities or subjective experience must rely on phenomenon X is an argument from ignorance plus ego” (emphasis changed). Well, I didn’t really mean any argument.

    But both the argument involving anesthetic and the one involving complexity theory have the flaw I was talking about: they rely on science’s alleged failure to provide a classical explanation and play on a feeling that human brains must have a very mysterious and special-sounding foundation.

  3. I think your analysis of the evidence for quantum effects in consiousness is excellent, but possibly misses the point. The reason (IMO) that some people invoke quantum theory to explain consciousness is that they think they can escape determinism that way. They are dismayed that the universe may be tightly deterministic in a way that takes away credit for their triumphs and blame for their failures.

    Although quantum effects are (or may be) non-determinisic, that doesn’t help. If our thoughts depend on the physical state of our brains, it doesn’t matter if that state is deterministic, or if Vanna White is spinning a virtual wheel in there somewhere. IOW, the physical state of our brain being in some sense non-deterministic doesn’t get win us credit for our good acts or get us off the hook for our sins.

    (Daniel Dennett did a much better job of making that point, but I think I got the gist of it here. I’m not a philosopher, I just play one in my imagination :-)

  4. Jkrehbiel:

    I agree with you, actually, to a considerable extent. The problem, though, is that people are uninformed on almost all aspects of the situation. They are told that classical physics is deterministic, but on pragmatic grounds, this is not true. Because they have this wrong idea which they find psychologically troubling, they seek solace in a bad understanding of quantum physics.

    Another complicating factor is that one cannot reason about physics by thinking about the everyday meanings of words. In their dark comedy Intellectual Impostures, Alan Sokal and Jean Bricmont mention a social-studies friend of theirs who asked them, in quite a puzzled manner, how it was that quantum mechanics could say the world was both discrete and interconnected? Looking at the everyday meanings of these two words, they do seem rather inconsistent; at least, though we could twist and turn using various definitions of these terms, we should forgive anyone who at first glance takes them to be contradictory.

    The short answer, Sokal and Bricmont say, is that scientists working with quantum phenomena do not use these words in their everyday senses, but give them meanings which depend upon a web of ideas, mathematical equations and experiments. (My best guess is that the social-studies person had heard about “entanglement,” which led to “interconnectedness,” while also receiving some garbled notion of “quantization,” the fact that systems like atoms come in states of different energies with nothing in between allowed.) One cannot think about physics as if it were a novel whose great themes were “chaos,” “probability” and “uncertainty!”

    It would be like studying music by looking only at the descriptions critics gave in reviews: “bright,” “rich,” “brooding,” “colorful,” etc.

  5. Blake,

    The same thing is true of biological concepts. Mention that something is “determined” genetically, and you get this ridiculous idea that having a genetic predisposition to do X requires you to do X no matter what, and that a genetic tendency toward philandering, for instance, somehow excuses men who cheat on their wives.

    John

  6. Good rant :-), and excellent commentaries. I didn’t know that mechanisms for anaesthetics had been found.

    But I vaguely remembered Penrose’s Gödelian argument, which as all the rest doesn’t tell us anything about the physical world but about how formal theories works. That it was combined with an appelation to unknown QG theories, I too hadn’t appreciated.

    In summary, a good reference about stuff some people want to woo the rest of us with.

    They are told that classical physics is deterministic, but on pragmatic grounds, this is not true.

    Good, but I would also complement the Laplacian argument against Newton’s clockwork universe with the observation of unpredictability in classical chaos. AFAIK the reentrant nature of these fully deterministic systems makes them blow up in our faces, so we would need infinite resolution to predict the outcome.

    Actually, I believe I once saw a paper proposing that infinite resolution could be used to beat the Church-Turing thesis and come up with the super-turing systems that Penrose in a way asks for. I’m not sure if the papers model was correct, but in any case these analog systems run up against problems of noise that loosely corresponds to the infinite resolution/resource requirement in the digital domain. (Or, ultimately, Planck effects.)

    some garbled notion of “quantization,” the fact that systems like atoms come in states of different energies with nothing in between allowed.

    I think this may be for historical reasons, because you can see the same notions in some text books while they work up to the modern theory.

    I.e. they start out with describing the motivations in the primitive quantum concept of Planck, over the introduction of the correspondence principle, before they leave the “discrete” description to recognize that fullblown QM is the one theory that seamlessly combines both discrete and continous states.

    In the atom picture, that would be the states when electrons ionize and are lifted to the continous energy band above the bound orbitals. ;-)

    Seems the world at large may be stuck somewhere in the early descriptions.

  7. Or, ultimately, Planck effects.

    Actually, we could throw in finite entropy and/or holography over the observable universe here too, to let the absence of infinite information further motivate why we can’t expect full predictability from recursive systems.

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