That was Then — This is Now
Last time, we left off Part I of what’s become a three-part blog postscript (is that even a thing?) with the observation that —
As with quantum decoherence itself, the problem with Max Tegmark’s reprise was its timing.
In a word, 2014 was late, maybe too late, in the game. Because …
(Well, you’ve already seen the headline.)
So, after slogging through the historical background, we’ve at long last arrived at the nub of the problem: If, as Max Tegmark claims, the brain is too “wet and warm” to sustain quantum coherence for the requisite few milliseconds needed to enable neuronal firing, then it’s pretty much game over, right?
Well, maybe — but, as luck would have it, even as Max was penning the passage referenced last time for inclusion in Our Mathematical Universe,[1] there was a lot else going on.
In effect, and despite the fact that Max’s “warm and wet” critique has been and keeps on being cited over and over (and over) again, it’s become kind of old news.
That’s because, starting in the early 2010s, there’d been a growing accumulation of experimental evidence (a.k.a. science’s touchstone) hinting that all manner of quantum phenomena might not only survive, but even thrive, in room-temperature scenarios.
What kind of scenarios?
Well, how about —
Photosynthesis
As early as 2007, a research team led by Gregory Engel of UC Berkeley reported they had gathered “direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes” in bacterial photosynthesis.[2]
Following up on the postulated phenomenon in both bacteria and plants, Rienk van Grondell and Vladimir Novoderezhkin noted that “long-lived [quantum] coherences could be observed at room temperature” and that “understanding the persistence of these quantum phenomena in such a noisy environment”remained an open issue.[3]
Now, admittedly this “long-lived” persistence isn’t much to write home about: Rienk and Vladimir estimated it at 500 femtoseconds (where one femtosecond equals 10-15 seconds), which is just a hair under Max’s 10-13-second lower bound for decoherence. (And even that would turn out to be an overestimation — the more commonly accepted timescale nowadays is that coherence in photosynthetic systems dephases in about 23 femtoseconds,[4] which puts it smack dab in the middle of Max’s lower-bound range.)
But that’s beside the point. The bottom line is that here we have evidence of a quantum phenomenon persisting over timescales which, however short, are evidently long enough to perform useful functions in living organisms.
What kind of functions? Well, according to Jeffrey Davis of the Swinburne University of Technology, “Quantum effects have been predicted to play a role in the very early stages of photosynthesis where efficient energy transfer between chromophores is required,” implying that “quantum coherence enables light energy to simultaneously investigate multiple pathways, and then choose the shortest, most efficient path, thereby leading to efficient energy transfer.”[5]
But maybe bacteria and plants don’t seem “warm and wet” enough to convince you. So, how about —birds?
Avian navigation
Ever since its discovery by Wolfgang Wiltschko back in the late 1960s, magnetoreception — the process by which birds sense the Earth’s magnetic field (and do so accurately enough to navigate migratory distances of thousands of miles) — has been a prominent research topic for the past half-century. But it’s only since the turn of the millennium that attention has shifted to the possibility that birds’ brains (more specifically, their retinas) are leveraging quantum effects to perform this particular task.
From the early 2000s on, investigators have been exploring the possibility that “birds use a light-induced radical pair reaction involving coherent spin evolution of two electrons as the foundation of their magnetic compass sensor.” By 2011, the role of this “radical pair mechanism” (or RPM) was being characterized as “[o]ne of the two major hypotheses” for how migratory birds find their way.[6] And, by the end of the decade, it had become “the dominant theory of compass magnetoreception.”[7]
So, what is RPM? It’s a quantum process by which atoms or molecules with an odd number of electrons (radicals) can pair up inside a protein in the avian visual system called cryptochrome. These pairs oscillate between a “singlet” and a “triplet” state, which fact can be used to detect the orientation of even the weak magnetic field generated by the Earth. Recent experiments on this“fundamentally quantum” oscillation have estimated that “the spin coherence lifetime of the magnetically sensitive radical pair is in the range [of] 2–10 μs [microseconds].”[8]
So, that’s about seven or eight orders of magnitude longer than the coherence lifetimes we saw in the photosynthesis example, but still anywhere from a hundred to a thousand times shorter than the neuron firing rate.
Still, the hypothesis is promising enough, and experimentally well attested enough, that the European Research Council was moved to provide the universities of Oxford and Oldenburg with a six-year Synergy Grant for a project called “QuantumBirds,” which “brings together quantum physics, spin chemistry, behavioural biology, biochemistry, and molecular biology in a unique, ambitious, imaginative and genuinely synergetic research programme that will prove whether the primary magnetic detection event occurring in the birds’ retinas involves the quantum spin dynamics of photochemically formed radical pairs in cryptochrome proteins.”[9]
That’s “prove” as in, well, prove, folks!
In the spirit of the old engineering maxim that “if a straight-line fit is desired, plot only two data points,” I believe we may be witnessing a trend here: One implying that, 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.
As I alluded to above, two examples is not a whole lot to hang a conclusion on. Still, recent research does seem to be pointing toward the distinct possibility that this trendline is going to hold true.
And that it’s going to top out at — wait for it — the human brain!
So, what is going on in the brain, anyway? That’ll be the central topic of Postscript, Part III, the final blogisode in this series. Watch for it next week!
Footnotes
[1] Max Tegmark, Our Mathematical Universe: My Quest for the Ultimate Nature of Reality, 2014, https://www.amazon.com/Our-Mathematical-Universe-Max-Tegmark/dp/0241954630/.
[2] Gregory S. Engel et al., “Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems,” Nature, 12 April 2007, https://www.academia.edu/15739382/Evidence_for_wavelike_energy_transfer_through_quantum_coherence_in_photosynthetic_systems/.
[3] Rienk van Grondelle and Vladimir I. Novoderezhkin, “Quantum effects in Photosynthesis,” Procedia Chemistry, Vol 3, No 1, 2011, pp. 198-210, https://www.sciencedirect.com/science/article/pii/S1876619611000660/.
[4] Erling Thyrhaug et al., “Identification and characterization of diverse coherences in the Fenna–Matthews–Olson complex,” Nature Chemistry, 2018; DOI: 10.1038/s41557-018-0060-5.
See also: University of Groningen, “Quantum effects observed in photosynthesis.” Science Daily, 21 May 2018, https://www.sciencedaily.com/releases/2018/05/180521131756.htm/.
[5] Lisa Zyga, “Study supports role of quantum effects in photosynthesis,” Phys.org, 25 January 2012, https://phys.org/news/2012-01-role-quantum-effects-photosynthesis.html/.
[6] Thorsten Ritz, “Quantum effects in biology: Bird navigation,” Procedia Chemistry, Vol 3, No 1, 2011, pp. 262-275, https://www.sciencedirect.com/science/article/pii/S1876619611000738.
[7] Siu Ying Wong et al., “Navigation of migratory songbirds: a quantum magnetic compass sensor,” Neuroforum, 2021, vol. 27, No. 3, pp. 141-150, https://doi.org/10.1515/nf-2021-0005/.
[8] Dmitri Kobylkov et al., “Electromagnetic 0.1-100 kHz noise does not disrupt orientation in a night-migrating songbird implying a spin coherence lifetime of less than 10 µs,” Journal of the Royal Society: Interface, 18 December 2019, https://pubmed.ncbi.nlm.nih.gov/31847760/.
[9] https://www.quantumbirds.eu/.
See also: University of Oldenburg, “Quantum Birds,” AAAS EurekaAlert!, 23 June 2021, https://www.eurekalert.org/news-releases/894145/.
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