Quantum Brains!
Last time we closed with:[1]
As we progress up the evolutionary ladder toward more and more complex organisms, there seems to be a concomitant tendency for quantum effects in those organisms to experience longer and longer coherence lifetimes.
… And recent research seems to be pointing toward the possibility that this trend line is going to top out at (where else?) the human brain.
So, yeah — let’s get on with that!
Microtubules redux?
Given where this series of postscripts started,[2] it’s only fair to point out that Sir Roger Penrose and Stuart Hameroff have far from given up on their microtubule-based Orch-OR proposal. On the contrary, in a 2016 essay,[3] they directly confronted Max Tegmark’s decoherence argument:
Tegmark (2000) published a critique of Orch OR based on his calculated decoherence times for microtubules of 10-13 s[econds] at biological temperature, far too brief for physiological effects. However Tegmark did not include Orch OR stipulations and in essence created, and then refuted his own quantum microtubule model. He assumed superpositions of solitons separated from themselves by a distance of 24 nm along the length of the microtubule. As previously described, superposition separation in Orch OR is at the Fermi length level of atomic nuclei, i.e., seven orders of magnitude smaller than Tegmark’s separation value, thus underestimating decoherence time by seven orders of magnitude, i.e., from 10-13 s to 10-6 s. Hagan et al. (2001)[4] used Tegmark’s same formula and recalculated microtubule decoherence times using Orch OR stipulations, finding 10-4 to 10-3 s, or longer.
So far, Max has responded with <crickets>.
In the meantime, for those of you who may have missed it, in a comment on the first Postscript blog, physicist and sf author David Brin remarked:[5]
The quantum effects don’t have to be of the time scale similar to neuronal activity. “Problems” can be delegated to microtubule quantum units that entangle electrons, ask them a question and the[y] decohere in an instant and then report to the neuronMurky, stochastic questions and outcomes that add up among thousands of tubules and create a basis [for] whether the neuron will fire. I got no problems with any of that.
It’s the ‘consciousness” part of it that seems mystically mumbo to me. If tubule-quantum can expand computational power by many orders of magnitude, well, it’s still computation.
I guess I’d have to agree with David that q-computation is still just computation — else wouldn’t any future q-computer necessarily become conscious?
(I’m not sure Sir Roger would agree, though, that what’s going on in the microtubules is “computation” in any conventional sense of the word: seems to me his whole argument from Goedel’s Incompleteness Theorems[6] is that conscious entities like us are capable of arriving at true conclusions which are not computable, not even in principle.)
Rather, for my money (all two cents of it), it feels like what Orchestrated-OR is trying to accomplish (via the notion of “orchestration”) is to provide some wiggle room for free will somewhere in between Newtonian clockwork determinism and utter quantum randomicity.
Regardless, the saga continues on from there, with no end in sight. Most recently, Stuart Hameroff has thrown down the gauntlet in an article purporting to show how easy it would be to falsify Orch-OR’s claims, and implicitly challenging the theory’s detractors to do just that.[7]
But in the meantime …
A New Spin on the Problem
It started almost imperceptibly: Back around the turn of the millennium, faint adumbrations of a new approach to quantum consciousness began emerging into the light, like the first tender crocus shoots poking out of a drift of late-winter snow.
Perhaps the best known of this first new crop of theories was the so-called “mind pixel” hypothesis put forward in 2002 by Huping Hu and Maoxin Wu.[8][9] Its signature contribution was to do away with microtubules altogether, and focus instead on the quantum phenomenon known as “nuclear spin.”
But just what is nuclear spin? Well, I don’t think it would be too much of a stretch to call it a metaphor.
Think of a figure skater performing a pirouette: She starts spinning slowly with her arms outstretched, but when she pulls them in close to her body, her spin speeds up. That’s conservation of angular momentum, one of physics’ hallowed conserved quantities.
Now, lose the skater and just keep the angular momentum.
Because electrons and other subatomic particles don’t actually spin — that’s the metaphor part. (For one thing, if they did, their surfaces would have to be moving faster than the speed of light, in violation of special relativity.) But they do have a quantum property that acts as if they were spinning — as though they had angular momentum, in other words.
In particular, passing a stream of such particles through a magnetic field will cause it to split into two discrete sub-streams, depending on whether their “spin” is “up” or “down” (apologies for the scare quotes, but it’s all metaphors from here on down, folks!).
For those hungering for a bit more detail on quantum spin in general (and, quite frankly, who isn’t?), you might want to check out Matt O’Dowd’s brief YouTube video.[10]
Alternatively, here’s how Kohei Itoh of Keio University explained it for a recent Future Learn course:[11]
You know that each electron has a spin, and the spin can be either aligned with the surrounding magnetic field, which we call spin up, or anti-aligned with it, which we call spin down. The nucleus of some types of atoms also has a spin. You probably know that the nucleus is composed of protons and neutrons. Besides charge and mass, these can give a nucleus a spin. …
But what’s the advantage, for present purposes, of nuclei over electrons here? Well, it all comes down to Max Tegmark’s old bugaboo: quantum decoherence.
Here’s Kohei again, pointing out that, as opposed to electrons in orbit around a nucleus —
Nuclear spins are actually already naturally protected. The electrons around the nucleus serve as a kind of shield, keeping the [environmental influences] away from the nucleus. … [T]he advantage is that we can keep the state exactly the way we want it for a long time.
Now, it’s important to note that Kohei isn’t talking about woo-woo, pie-in-the-sky concepts like quantum consciousness here. No, he’s an active participant in the race to build the world’s first quantum computer, a generational research effort that’s currently costing big-tech giants like Google, Amazon, and Microsoft billions of dollars this year alone![12]
And one other thing from the above quote that bears repeating: the advantage of leveraging nuclear spin for q-computing is that “we can keep the state exactly the way we want it for a long time” — even, as it turns out, in the face of decoherence.
How long a time, especially in “warm and wet” environs like the human brain? Well, we’re getting to that.
But to get there, we’ve first got to take something of a detour into the intellectual odyssey traveled by Kavli Institute for Theoretical Physics professor and founder of Kavli’s Quantum Brain project, Matthew Fisher.
… An odyssey that took Matt all the way from what he calls “conventional” condensed matter physics (in which research area he won the 2015 Oliver E. Butler Prize) to what he calls “quantum neuroscience.”[13]
… An odyssey that began in 2013, when he was pondering the unreasonable efficacy of lithium in treating mania and bipolar disorder.
… Because, curiously, unlike Prozac and other macro-molecular medications, lithium is a simple elementary, well, element. And the mystery of its effectiveness only deepened when Matt realized that, of its two stable isotopes (the commonly occurring lithium-7 and the much rarer lithium-6), the latter had much stronger psychotropic effects.
Matt described his initial astonishment as follows:
How could that possibly be, I exclaimed loudly and emphatically … Bio-chemistry depends on the number of electrons in an atom/ion, and is largely insensitive to the number of neutrons in the atomic nucleus (3 vs. 4, for the lithium-6 and lithium-7 isotopes, respectively).
Yet not only did lithium-6 yield much stronger effects than its isotope — it also sported much, much longer quantum coherence lifetimes:
… [W]hen Google told me that the quantum coherence time of the nuclear spin of a lithium-6 ion when solvated in water is a whopping 5 minutes (!) — roughly the same as my [short-term] memory, and much longer than lithium-7’s coherence time of 10 seconds — the remarkable possibility that quantum processing with nuclear spins might be operational in the brain was placed firmly in my own brain!
In other words, there appears to be, pace Tegmark, what Matt calls a “loophole” in the decoherence death-trap.[14]
… [W]ith different numbers of neutrons in their atomic nucleus the nuclear spin properties of the two lithium isotopes are very different, these considerations raise the remarkable possibility that nuclear spin processing might be operational in the brain. If present this processing would be quantum processing since the nuclear spin is quantized. Might the brain have evolved to enable cognitive quantum processing?
To Matt, the implications were clear:
If there is quantum processing operational in the brain, it is going to require degrees of freedom (neural qubits) which are isolated. So we can ask, what degrees of freedom, if any, are isolated from the wet environment in biology? There is only one answer: nuclear spins. …
For a given nucleus it is possible to use NMR [i.e., Nuclear Magnetic Resonance] to measure a nuclear spin decoherence time, the time that it takes for the nuclear spin to quantum entangle with its environment. For example, the decoherence time of the sodium nucleus when a sodium ion is floating in water is roughly a tenth of a second – long on microscopic timescales but not long on human timescales.
However …
These decoherence times vary between the elements. For a Li-7 ion solvated in water the nuclear spin decoherence time is about 10 seconds. Remarkably, a solvated Li-6 ion has a nuclear spin decoherence time of five minutes! That is a long time. Perhaps longer than my own aging memory.
Accordingly, Matt went searching for an element within the brain that might serve as a biological equivalent of the quantum bits (or qubits) on which quantum computation is based. And he thinks he’s found a likely candidate in potassium-based Posner clusters. More on that here[15] — this blog’s gotten way too long as it is.
In any case, if Matt Fisher’s speculations prove out, you can forget about Max Tegmark’s femtosecond longevity limits — Matt’s talking about a nuclear spin decoherence time measured in minutes, maybe even hours!
Matt’s ballpark estimate is somewhere between fifteen minutes and eleven and a half days!
It’s beginning to look, in the words of Oxford University’s Vlatko Vedral, as if the idea that a warm, wet brain is too messy to have useful coherences is “simple-minded.”[16]
As noted, all this still lies in the realm of speculation at this point, but already it’s shown enough promise that the Heising-Simons Foundation[pp] has ponied up $1.5 million for a three-year grant funding a “Quantum Brain” (or QuBrain) collaboration at the Kavli Institute.[17]
* * *
Well, that’s pretty much it for me. I’ve taken my best shot at laying out the case for quantum consciousness. And, while I don’t imagine I’ve managed to convince everyone, I hope, at the very least, to have shown that there’s enough to it to merit serious scientific consideration, rather than just an out-of-hand “warm and wet” dismissal.
Footnotes
[1] http://www.billdesmedt.com/the-making-of-a-thriller-part-iv/.
[2] http://www.billdesmedt.com/the-making-of-a-thriller-ps-part-i/.
[3] Stuart R. Hameroff and Roger Penrose, “Chapter 14. Consciousness in the Universe: an Updated Review of the ‘Orch-OR’ Theory,” in R. R. Poznanski et al. [eds], Biophysics of Consciousness: A Foundational Approach, World Scientific, 2016, https://galileocommission.org/consciousness-in-the-universe-an-updated-review-of-the-orch-or-theory-hameroff-2016/.
[4] Hagan, S., Hameroff, S. & Tuszynski, J. “Quantum computation in brain microtubules? Decoherence and biological feasibility,” Phys. Rev. E, 65, 061901.
[5] David Brin on 2021-09-13 at 5:15 pm, Comment #2, http://www.billdesmedt.com/the-making-of-a-thriller-ps-part-i/, infra.
[6] Roger Penrose, The Emperor’s New Mind, 1989, https://www.amazon.com/Emperors-New-Mind-Concerning-Computers-ebook/dp/B074JCG4P9/.
[7] Stuart Hameroff, “‘Orch OR’ is the most complete, and most easily falsifiable theory of consciousness,” Cognitive Neuroscience, 24 November 2020, DOI: 10.1080/17588928.2020.1839037, https://doi.org/10.1080/17588928.2020.1839037/.
[8] Huping Hu and Maoxin Wu, “Spin-mediated Consciousness Theory: Possible Roles of Oxygen Unpaired Electronic Spins and Neural Membrane Nuclear Spin Ensemble in Memory and Consciousness, v1,” 11 August 2002, https://arxiv.org/pdf/quant-ph/0208068v1.pdf/.
[9] Huping Hu and Maoxin Wu, “Spin-mediated consciousness theory: possible roles for neural membrane nuclear spin ensembles and paramagnetic oxygen,” Medical Hypotheses, 2004, vol 63. No 4, pp. 633-648, https://www.sciencedirect.com/science/article/abs/pii/S0306987704002440/.
[10] Matt O’Dowd, “Electrons DO NOT Spin,” PBS Space Time, https://www.youtube.com/watch?v=pWlk1gLkF2Y/.
[11] Kohei Itoh, “Nuclear Spin,” https://www.futurelearn.com/info/courses/intro-to-quantum-computing/0/steps/31585/.
[12] “Quantum computing is at an early stage. But investors are already getting excited,” Investors News, 15 September 2021, https://investorsnews.net/2021/09/15/quantum-computing-is-at-an-early-stage-but-investors-are-already-getting-excited/.
[13] Matthew Fisher, “Quantum Brain,” UC Santa Barbara, Kavli Institute for Theoretical Physics, https://www.kitp.ucsb.edu/mpaf/quantum-brain/.
[14] Matthew Fisher, “Are we quantum computers or merely clever robots?” Talk presented at the Conference on 90 years of Quantum Mechanics, Nanyang Technological University, Singapore on 24 January 2017, Asia-Pacific Physics Newsletter, April 2017, vol 6, No 1, pp. 39-46, https://www.kitp.ucsb.edu/sites/default/files/users/mpaf/p178a_0.pdf/.
[15] Nicole Yunger Halpern and Elizabeth Crosson, “Quantum information in the Posner model of quantum cognition,” 28 May 2019, https://arxiv.org/pdf/1711.04801/.
[16] Michael Brooks, “A bit in two minds,” New Scientist, 2 December 2015, https://www.newscientist.com/article/mg22830500-300-is-quantum-physics-behind-your-brains-ability-to-think/.
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