According to the paper by Koch and Hepp The relation between quantum mechanics and higher brain functions: Lessons from quantum computation and neurobiology from 2007, quantum mechanics and its indeterminism is not relevant to explain consciousness.

The interaction of neurons – "a 300 Kelvin wet and warm tissue strongly coupled to its environment" - is governed by classical physics.

On the other hand, a minority of neurobiologists and physicists maintains "that quantum mechanics is important for understanding higher brain functions, e.g. for the generation of voluntary movements (free will), for high-level perception and for consciousness.”

What is the state-of-the-art concerning the question from the heading?

In particular, it would be helpful to learn the assessment from users who are familiar with both fields, quantum mechanics and neuroscience.

Note: My question is triggered by several comments from @Double Knot.

  • 1
    This seems a bit too far outside the scope of philosophy, as neither quantum mechanics nor neuroscience are within philosophy. Questions about the epistemic implications of QM may be on topic, for example, but this question just seems to be speculative about what quantum mechanics or neuroscience may one day discover about how the brain works.
    – NotThatGuy
    Oct 12, 2023 at 9:13
  • 3
    @NotThatGuy I hope that philosophy is interested in what science can explain about consciousness.
    – Jo Wehler
    Oct 12, 2023 at 9:19
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    Explaining free will by the indeterminacy of quantum events is just kicking the can down the road. Let's say it's actually quantum phenomena that explain why our actions are not fully determined by the initial conditions, that would give us the "free" in "free will". But we still need to explain what the "will" is, how our spirit or soul or something is able to pilot those billions of quantum interactions in order to produce the desired bodily movement.
    – armand
    Oct 12, 2023 at 13:46
  • 2
    I just love the tag "neurophilosophy". Least we forget, neurons are cells and nerves are organs, like the heart or the liver. "Hepathophilosophy" or "cardiophilosophy" make just as much sense as "neurophilosophy".
    – Olivier5
    Oct 12, 2023 at 18:10
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    The “warm, wet, and noisy” line about the brain goes back to Tegmark's 1999 paper. The problem is that we know examples of macroscopic amplification of quantum effects (Geiger counters, superfluids, superconductors) and one cannot conclusively rule out that some such mechanism is in play somewhere in the brain based on generic thermodynamic considerations like Tegmark's. Some quantum effects in biology are known, but so far no conclusive evidence of their role in human brain either.
    – Conifold
    Oct 13, 2023 at 5:44

7 Answers 7


At present, I find it hard to see right now how the brain itself can support useful quantum coherence, and to what degree that even addresses issues like free will, information binding, and subjective continuity.

Let's say that the quantum brain hypothesis is correct, and that we are able to identify the physical processes that constitute conscious states. We are still left with the question

"Why are entangled states associated with a subjective experience?"

In other words, a physical theory explaining the arising of consciousness "from the outside" still can't replicate the qualia associated with that state. If we could do that, we could know exactly what it is like to be, say, a dog or chimpanzee -- not merely by analogy, but by direct translation of their brain state to the correct qualia.

Anyway, as others have said - too early to tell. I think the resolution, if it ever comes, will be quite disrupting regardless :)

Further reading

A great place to start any new philosophical inquiry is the Stanford Encyclopedia of Philosophy. It's been around since 1995 and at this point is extremely vast in its topical coverage and the articles are usually well maintained by philosophers.

In particular, there is a (fairly lengthy) article on just this topic: https://plato.stanford.edu/entries/qt-consciousness/

I've personally studied Penrose-Hameroff's OrchOR theory the most, it's very speculative but interesting. More broadly, I like the idea of dual-aspect theories, especially neutral monisms that consider mind-matter to be simply correlated via a neutral reality. and a few have been fleshed out mathematically quite a bit.

  • I don't think we would know what it's like to be a bat just because we could perform the calculations.
    – wizzwizz4
    Oct 13, 2023 at 9:12
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    – Community Bot
    Oct 13, 2023 at 9:47
  • @wizzwizz4 that is exactly my point — it’s an argument against physicalism.
    – Annika
    Oct 13, 2023 at 12:03
  • @Annika No, I mean: humans aren't good at holding all that in our heads. That's why we do calculations on paper, or get computers to do it, and why it takes a decade of mathematics education to understand a book's worth of material. We might be able to learn what it's like to be a fruit fly, but probably not a dog, bat, chimpanzee or dolphin.
    – wizzwizz4
    Oct 13, 2023 at 12:20
  • @wizzwizz4 you'd have to explain how we'd create the qualia that are associated with being a fruit fly - that's what I'm getting at. There's the calculations, the outputs, the understanding, but qualia are none of those they are the experience itself and the explanatory gap is that we don't know how or why knowing something from the outside would ever lead to experiencing the qualia they describe (we seen to only be able to understand qualia by direct experience)
    – Annika
    Oct 13, 2023 at 15:50

We are not even close to having a solid theory of how consciousness arises from, or is facilitated by, chemical activity in brains, so it is too early to rule quantum effects in or out. The Koch and Hepp paper addresses the point that the brain can hardly be capable of supporting macroscopic quantum effects, because it is far too noisy an environment. However, that doesn't mean that quantum effects are not in play at all. It is possible that particular microscopic steps within the highly complicated processes that correlate with thought are subject to quantum effects, and that could be sufficient to prevent the brain from being considered to behave in an entirely classical way, which therefore opens up the possibility that we are not simply classical automata. That all said, introducing quantum indeterminacy is in itself hardly sufficient to explain consciousness and free will.


The paper you cited focused on macro-scale quantum coherence, although it discusses several other quantum theories of conscious interaction. The decoherence cited at the macro level is targeted against Stapp's thinking, not the other two. The other two face different problems, and all three hypotheses are probably incorrect, but that is for diverse reasons, specific to each. These three though do not exhaust how QM can effect macro scale indeterminist openness for physics.

That these three are each probably wrong does not show that efforts to vector off QM to address the "hard problem of consciousness" are flawed, or inappropriate in any way. The process of both philosophy and science involves developing a lot of interesting and possibly useful hypotheses, most of which ultimately fail.

There are no doubt many other ways that QM could be integrated into a proposed solution. There is one area that I consider has tremendous potential. The leveraging up of quantum effects to macro scale in chaotic systems is a subject that has not been fully understood or explored, and was not addressed in the paper. It was implicit in the way a single quantum effect was cited as triggering a human eye, but the inference that this event then can trigger a thought, and possibly an action was not pursued.

That brains can be influenced by a single quantum event in a retina demonstrates that brains are unstable chaotic structures, and the linear/stable assumption behind the expectation that quantum events will fade out into the averaging of large numbers is -- unjustified.

HOW quantum events would then provide control of a brain, or trigger consciousness, is less obvious. Chaotic systems are notably hard to control or steer. And any Identity Theory between quantum events and consciousness has the same problem that all other identity theory speculations have -- we DON'T have consciousness in all sorts of brain states and activity events, hence there is no identity.

BUT -- the chaotic nature of our brains, plus the indeterminate nature of quantum events that can influence our brains, open up the logic space for libertarian free will and a dualist interaction system to be logically possible.

  • The objection to libertarian free will is not that it's not "logically possible", it's that it's poorly defined, not supported by any evidence, and incoherent (pure randomness meets the common definition of free will, of the ability to have acted differently, yet randomness contradicts having any sense of non-arbitrary conscious control, i.e. "will"). If you embrace randomness, you may help with the first 2 problems, but then we're left with the far bigger problem of simply assigning the label of "free will" to something that in no way reflects how the term is understood.
    – NotThatGuy
    Oct 12, 2023 at 10:58
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    @NotThatGuy -- There are assumptions embedded in causation and classical logic thinking that make both conscious causation and free will both problematic. The realization in physics that the indeterminacy intrinsic to QM leverages up to the macro scale thru chaotic sensitivity for a large number of life processes shows that contemporary physics at life scale can be both logically and causally open. Both emergent and spiritual consciousness could in principle use this discovery to be causal. This is the question, and my answer focusses on that insight/discovery.
    – Dcleve
    Oct 12, 2023 at 15:21
  • @NotThatGuy Free will also requires a causal logic that does not use your determined/random dichotomy (or trichotomy, as QM uses a fusion that is not either, but a mix of the two, but this fusion does not enable willing either), and that is a different/separate question. Logicians have realized that there are infinite different logics (logical pluralism), which provides a solution if one finds a logic that works for free willing. Agent Causation is what free will needs, and there are philosophers actively trying to develop agent causation logics. This addresses your "possible" concern.
    – Dcleve
    Oct 12, 2023 at 15:28
  • My point is that chaos doesn't seem to open the door to anything. If you want to posit some incompatibilist idea of free will that isn't just randomness, you need some additional mechanism, whether randomness exists or not.
    – NotThatGuy
    Oct 12, 2023 at 16:38
  • All QM does is allow people (laypeople, mostly) to convince themselves that such a mechanism exists, even if we still have no idea what the mechanism is or how it works or anything. It's also a poor explanation for our QM observations - it's supposed to apply to consciousness and grant free will, but QM applies to a whole lot of things that have no indication of consciousness, nor any will whatsoever, and we can consistently influence QM particles (which undermines the idea that they can grant will).
    – NotThatGuy
    Oct 12, 2023 at 16:40

In my opinion quantum mechanics in most of the cases irrelevant to explain conscious processes. However people like Deepak Chopra believes otherwise.

I have not yet found quantum mechanics playing a role in body processes or emotional processes or perceptual processes or choice making processes or consciousness processes.

However if you have been studying quantum mechanics then it definitely has an effect on your consciousness. It leaves you with mystery and a feeling of awe and amazement. You become suspicious of reality and tend to believe that things are not what they seem to be. In this sense quantum mechanics has an effect on your psyche if you study it properly.

  • I'm not convinced that actual scientists ("properly") studying quantum mechanics are generally "suspicious of reality". Reality is what it is. Science seeks to understand how it works. If you find some non-deterministic building blocks to deterministic processes, that might lead you to explore how the former forms the latter (or whether it's actually non-deterministic), but that's just doing science. This doesn't reverse all the evidence we have of macroscopic events being deterministic.
    – NotThatGuy
    Oct 13, 2023 at 8:43
  • Science may lead to seemingly uncomfortable conclusions sometimes, but scientists tend to be okay with those, because they want to understand reality as it is (although that hasn't historically always been the case: evolution, to name one thing, was opposed when first proposed... but the evidence just because too overwhelming to deny). Laypeople are more likely to become "suspicious of reality" from some exposure to QM.
    – NotThatGuy
    Oct 13, 2023 at 8:48

Scientific theories do not govern reality. They model it, which is very different. So the authors of the paper are wrong-footed from the get go. They confuse scientists with governors.

Beside, "classical physics" is synonymous to 19th century physics. It's outdated science, and as such, it cannot possibly "govern" anything.

How could the authors of the article linked in the OP be so wrong in their very first paragraph?

My hypothesis is that they desperately want to "save" the determinist outlook that they attribute (wrongly) to classical physics. The indeterminism inherent to QM scares them, unsettles them, and it pisses them off that scientits might seriously consider indeterminate brain functions.

That'd be why they start their paper with this rather odd sentence: "The relationship between quantum mechanics and higher brain functions is an entertaining topic at parties between a mixed, open-minded group of academics." (emph. added)

Hence their efforts to try and keep QM away from neuroscience. Unfortunately for them, the idea that the world is neatly divided between a macroscopic level ("governed" by 19th century physics) and a microscopic level ("governed" by 20th and 21st century physics) is even more wrong-footed than the idea that science governs anything.

It's one world, least we forget. Scale is in the eye of the beholder.

Radioactivity is a sub-atomic phenomenon, yet it can kill you.

When a neuron "fires", it generates electricity and radio waves. That is: electrons and photons, whose behavior is best modeled by QM.

We have very little sense of what consciousness is and how it is generated. To rule out any sort of scientific explanation appears premature to me, based on strictly nothing else than prejudice.

  • "Classical physics" is demonstrated by countless experiments by countless scientists over centuries. Calling it "outdated" suggests all those results have now been invalidated, which is not at all the case. "Classical physics" continues to be immensely useful for modelling and predicting how things will behave. Quantum mechanics is (at least so far) mostly relevant to microscopic study, whereas you'd probably be wasting your time trying to incorporate QM into e.g. modelling how planets move (I mean in general - if you're specifically studying QM's effects on that, if any, that's different).
    – NotThatGuy
    Oct 13, 2023 at 8:57
  • @NotThatGuy The orbit of Mercury contradicts "classical physics". I could go on and on. It's outdated, period. No need to clinch on it like if it was some gospel. I understand that materialists cannot let it go, though, since their entire worldview would collapse if they were to accept modern science.
    – Olivier5
    Oct 13, 2023 at 11:31
  • Sure, just ignore all the justification I just gave for my position, and then insult me a bunch for "clinging" to the position, instead of, you know, having a justification for it. It sure is convenient to make arguments when you just ignore whatever you want. And when you only provide one example, that brings into question whether you could, in fact, "go on and on". As for your one example where "classical physics" is supposedly lacking, you've apparently completely failed to understand my point about the many places that classical physics has precise predictive power.
    – NotThatGuy
    Oct 13, 2023 at 12:12
  • As an aside, I also haven't seen a prominent QM-based explanation for Mercury's orbit - if there isn't one, that would demonstrate your failure to understand how science works - you don't discard a model until you have one that better explains the data. I'd honestly be surprised if you can find even one single scientist who'd claim that general relativity is "outdated" (maybe there are some, but it's certainly not the consensus). For someone accusing others of dogmatically rejecting "modern science", you sure are quick to dismiss the bulk of actual scientists.
    – NotThatGuy
    Oct 13, 2023 at 12:12
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    @NotThatGuy errr... General relativity is evidently not "classical physics", it is not outdated, and it does explain Mercury's orbit far better than "classical physics" aka Newton.
    – Olivier5
    Oct 13, 2023 at 13:32

From a physics perspective:

Quantum processes dominate on scale lengths of less than an atom diameter. Since energies scale as inverse distance in natural units, the quantum world makes its presence felt on macro scales with extremely high-energy particles (alpha particles, beta particles, neutrons, etc.) and photons (gamma rays) which originate from inside the nucleus of an atom.

Both those particles and photons are sufficiently energetic that a protein molecule struck by one is destroyed on the spot. This is why alphas, betas and gammas are deadly to humans.

This means a protein molecule (as contained in a neuron for example) can't "talk" to a quantum process without being instantly killed.

This fact makes me unsympathetic to efforts intended to explain things like consciousness in terms of quantum processes.


No physics, quantum or classical, is relevant to explain conscious processes.

Psychology and brain physiology are completely different branches of science studying completely different processes that play by completely different rules.

Mental processes, conscious or unconscious, have no physical properties at all, they don't deal with matter or energy.

  • Do you know that Eric Kandel in his book “Psychiatry, psychoanalysis and the New Biology of Mind”, amazon.de/Psychiatry-Psychoanalysis-New-Biology-Mind/dp/…, argues even for bridging neurobiology and psychotherapy?
    – Jo Wehler
    Oct 13, 2023 at 7:38
  • 4
    There are strong, repeatedly observable correlations between brain states/processes and mental experience. Unless these correlations are entirely coincidental, how could physics be irrelevant to a phenomenon (consciousness) that is, as far as we can tell, the result of/intertwined with brain function? Oct 13, 2023 at 8:35
  • @Futilitarian Of course the mental and the physical are deeply interconnected in the brain, but there is no 1to1 correlation. There is a very strict division of labour. Physical processes cannot do anything mental (experience, imagine or decide) and vice versa: mental processes cannot do anything physical (move matter or energy). Oct 13, 2023 at 9:42
  • So, if "Of course the mental and the physical are deeply interconnected in the brain", how can you say that physics (which underlies brain processes) is irrelevant to conscious processes? Oct 13, 2023 at 10:02
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    @PerttiRuismäki If brain physiology doesn't interfere with mental processes, that seems to suggest that brain injury would not by itself change someone's personality, yet we have plenty of evidence of that happening.
    – NotThatGuy
    Oct 13, 2023 at 11:10

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