A weird phenomenon in the physical sciences is when the aging lions of the field veer into areas outside their competence and start making silly claims. Saturday Morning Breakfast Cereal has an awesome comic strip about it.
Linus Pauling convinced people that megadoses of vitamin C cured the common cold. Equally silly is the quantum woo of brilliant physicist Roger Penrose, who believes that mysterious quantum processes underlie the phenomenon of consciousness.
The quantum consciousness idea has been through a series of incarnations. First Penrose suggested that tiny structures inside neurons, called microtubules, actually acted as qubits. A qubit is a type of quantum-mechanical unit of information, the quantum analog of a bit. It can exist simultaneously in both of the 0 and 1 states, like Schrodinger's cat. It also has a quantum-mechanical property called phase, which in a classical metaphor you can visualize as the wobbling of a spinning top. In a quantum computer, a network of qubits have their phases tied together in a complicated network of long-distance interconnections.
These phase correlations are extraordinarily delicate. Real-world quantum computers, which are still very primitive, are fussy high-tech systems that have to be cooled down to cryogenic temperatures. So it's inherently extremely implausible that an object as warm, wet, and messy as the human brain could be a quantum computer. Nor is there any good argument to support Penrose's claim that consciousness can't happen without some kind of quantum fairy dust to make it go.
Penrose's idea was immediately refuted. For example, physicist Max Tegmark estimated that the quantum correlations in objects the size of microtubules were so delicate that they would be destroyed within 10^-13 seconds -- about a billionth of the shortest time-scales involved in signal processing by the nervous system. As often happens with this kind of gee-whiz pseudoscience, Pensose responded by elaborating his ideas, without admitting that they were fundamentally implausible and unnecessary for explaining consciousness. He calls his latest rebranding of the idea "Orch OR."
As objects get bigger, it gets more and more difficult to make them exhibit quantum correlations for any amount of time before they get scrambled. That was why Penrose initially proposed the microtubules inside neurons -- he was looking for the most microscopic anatomical features he could think of. Since estimates like Tegmark's show that that's impossible, more recent proposals, by people like UCSB physicist Matthew Fisher, have focused on even smaller objects, molecules called Posner clusters. Work by Litt et al., Koch and Hepp, and McKemmish et al. have pointed out multiple independent reasons why quantum woo isn't especially relevant in efforts to explain consciousness (Litt 2006) and why the concept of quantum consciouness just doesn't work scientifically.
The whole sad story reminds me of the notion that radio waves could cause cancer, which started in the days before cell phones and never made any sense in terms of the fundamental physics: radio waves are too low in frequency to be able to ionize atoms, so when they interact with your body, all they can do is heat you. But my generation was nevertheless told not to use electric blankets or stand too close to the microwave, because we would get cancer. Biologists and epidemiologists spent decades on quixotic attempts to use biology to probe this question that was really a non-starter at the basic physical level. Only when cell phones came along did this junk science start to peter out, since nobody wanted to imagine that the phone they were holding against their head could be giving them brain cancer -- but there are still kooks in my neighborhood who believe that our high school's 5G network is an evil health hazard.
Along the same lines, people are spending grant money these days on things like NMR studies to see whether quantum correlations could be more robust than expected if they're partially shielded by their molecular environment, as well as an in vivo MRI study of the human brain that has been greatly ballyhooed on social media (Kerskens and López Pérez, 2022). Even if the Kerskens results are correct, the observation of correlations in the nervous system does not imply that the correlations are quantum correlations. The situation is similar to the one surrounding radio waves and cancer, because the physics doesn't make sense based on very basic principles. But once the claims are unleashed, people start doing biological studies, as if that could trump the underlying absurdity of it.
Ben Crowell, 2022 Nov. 29
Kerskens and López Pérez 2022 J. Phys. Commun. 6 105001 DOI 10.1088/2399-6528/ac94be https://iopscience.iop.org/article/10.1088/2399-6528/ac94be
Koch, C., & Hepp, K. (2006). Quantum mechanics in the brain. Nature, 440(7084), 611–611. doi:10.1038/440611a https://sci-hub.se/10.1038/440611a
Litt et al., 2006, Is the Brain a Quantum Computer?, https://sci-hub.se/https://doi.org/10.1207/s15516709cog0000_59
McKemmish et al., 2009, Penrose-Hameroff orchestrated objective-reduction proposal for human consciousness is not biologically feasible https://sci-hub.se/https://doi.org/10.1103/PhysRevE.80.021912
Tegmark, M. (2000). Importance of quantum decoherence in brain processes. Physical Review E, 61(4), 4194–4206. doi:10.1103/physreve.61.4194, https://sci-hub.se/10.1103/PhysRevE.61.4194