ii) The Quantum Scale and the Large Scale
iii) The Brain and Quantum Gravity
iv) Daniel Dennett’s Quantum Car
Throughout Roger Penrose’s writings on the brain, consciousness, physics and cosmology, the issue of the link between the quantum scale and the large (“classical”) scale is constantly broached. Indeed all this strongly links in with Penrose’s attempt to tie general relativity/gravity and quantum mechanics together.
Penrose’s own individualistic position on the relation between the quantum scale and the large scale is expressed in the following:
I am not concerned so much with the effects that quantum mechanics might have on our theory (Einstein’s general relativity) of the structure of space-time, but with the reverse: namely the effects that Einstein’s space-time theory might have on the very structure of quantum mechanics.Roger Penrose
This is (as Penrose himself puts it) “an unconventional view-point” — or it was in 1990. It’s “unconventional that general relativity should have any influence at all on the structure of quantum mechanics!” More basically, Penrose believes that “the problems within quantum theory itself are of a fundamental character.”
In terms of the brain and mind, Penrose concluded — again, 28 years ago — by saying that “any putative quantum gravity theory would surely be very remote from the phenomena governing the behaviour of brains.”
Nonetheless, the following is the crux of Penrose’s current position:
- Quantum gravity (or the “structure of space-time”) may have an impact on quantum mechanics.
- Therefore quantum gravity may affect the nature of the brain and mind.
At the most basic level, gravitation and general relativity aren’t integrated into quantum theory. That alone makes Penrose’s views on the brain, mind and consciousness speculative.
In terms of the brain and mind/consciousness, most neuroscientists and many philosophers believe that quantum phenomena (or quantum events/effects/conditions/etc.) have very little effect on the brain and therefore on the mind/consciousness as a whole. Or, at the very least, that the differences they do make don’t really make a difference.
The Quantum Scale & the Large Scale
As stated above, Penrose notes the micro-macro situation in ways that don’t directly relate to the brain and mind. In the following, for example, he notes the contextual (i.e., micro or macro) nature of the notion of randomness (or probabilities). That is, Penrose notes how randomness is a consequence of scientists observing quantum effects/events/conditions/etc. at the “classical level”. In Penrose’s own words:
Since randomness comes in, quantum theory is called probabilistic. But randomness only comes in when you go from the quantum to the classical level. If you stay down at the quantum level, there’s no randomness. It’s only when you magnify something up, and you do what people call ‘make a measurement’. This consists of taking a small-scale quantum effect and magnifying it out to a level where you can see it. It’s only in that process of magnification that probabilities come in.Penrose
This can be deemed to be an epistemic problem, rather than an ontological one. That is, the probabilities (or randomness) arises not from the ontology of the quantum world, but from our epistemic access to it. (This conclusion, at least as it partly applies to quantum indeterminism, dates back to Albert Einstein and was elaborated upon by such people as David Bohm.)
The other point that’s worth making about Penrose’s position (as quoted above) is that it goes against the stress on quantum indeterminism as it’s often used in reference to the brain and mind/consciousness. In other words, Penrose (at least in this context) is de-stressing the random (or indeterministic) nature of the quantum realm; whereas many others (at least in the debate about mind) play it up. (“Quantum indeterminism” is particularly stressed as one explanation of free will.) Of course it must be said here that the words “random” and “indeterminate” (or “randomness” and “indeterminacy”) aren’t exactly synonyms. Nonetheless, in the debate about the “quantum mind” (as it’s often put), these words are indeed often treated as synonyms (or, at the very least, as near-synonyms).
If we now return to the quantum scale and the large scale.
On a much broader level we can also take Brian Greene’s (a Professor of Physics and Mathematics at Columbia University) general point about this micro-macro distinction:
It’s not as though the universe comes equipped with a line in the sand separating things that are properly described by quantum mechanics from things properly described by general relativity. Dividing the universe into two separate realms seems both artificial and clumsy.Brian Greene
This position seems to back up Penrose’s previous points about how different levels of description (which are brought about by the effect of “measurement”/observation) determine Greene’s “line in the sand” between the quantum realm and the “classical” realm.
And, yet again, Penrose notes these different levels when he talks about Newtonian mechanics, relativity and quantum theory. He stresses the compatibility of these different levels of description/application and their respective “limits”. He says:
Current physics ideas will survive as limiting behavior, in the same sense that Newtonian mechanics survives relativity. Relativity modifies Newtonian mechanics, but it doesn’t really supplant it. Newtonian mechanics is still there as a limit. In the same sense, quantum theory, as we now use it, and classical physics, which includes Einstein’s general theory, are limits of some theory we don’t yet have.Penrose
In the above we can see that rather than measurement (or observation) splitting the universe into two realms, Penrose stresses the respective “limits” of these realms instead.
The Brain & Quantum Gravity
Roger Penrose was — and still is — deeply aware of the arguments against his central position on the brain and mind/consciousness. Indeed when he wrote The Emperor’s New Mind (in 1990)he didn’t have an original position on the quantum nature of the brain. Specifically, microtubules aren’t mentioned in this well-known book. And even neurons and neurotransmitters only get four mentions.
This is what Penrose also had to say (in the same book) on the opposition’s position on the brain, quantum mechanics and consciousness:
… they would argue that on a scale relevant to our brains the physical effects of any quantum gravity must be totally insignificant! They would say (very reasonably) that although such physical effects might indeed be important at the absurdly tiny distance scale known as the Planck length — which is 10⁻³⁵ m, some 100000000000000000000 times smaller than the size of the tiniest subatomic particle — these effects should have no direct relevance whatever to phenomena at the far far larger ‘ordinary’ scales of, say, down only to 10⁻¹² m, where the chemical or electrical processes that are important to brain activity hold sway.Roger Penrose, in “The Emperor’s New Mind”
In fact Penrose went further by saying that his detractors would claim that not even ordinary gravity (as it were) can affect the brain. He wrote, “Indeed, even classical (i.e. non-quantum) gravity has almost no influence on these electrical and chemical activities.”
Penrose concluded with the following skeptical words. (At least as he then believed that they’d be expressed by his opponents.) He wrote:
If classical gravity is of no consequence, then how on earth could any tiny ‘quantum correction’ to the classical theory make any difference at all? Moreover, since deviations from quantum theory have never been observed, it would seem to be even more unreasonable to imagine that any tiny putative deviation from standard quantum theory could have any conceivable role to play in mental phenomena!Penrose
Thus, at this period in Penrose’s career (in the early 1990s), his position squared perfectly well with Murray Gell-Mann’s later position when Gell-Mann wrote:
… what characterises [Roger Penrose’s] proposal… is the notion that consciousness is somehow connected with quantum gravity — that is to say, the incorporation of Einsteinian general-relativistic gravitation into quantum field theory. I can see absolutely no reason for imagining such a thing.Murray Gell-Mann
And all this brings us to Dennett’s quantum car.
Daniel Dennett’s Quantum Car
Daniel Dennett put this micro-macro quandary very well. He argues (to paraphrase), ‘Sure, there are quantum happenings in the brain or neurons. Then again, there are quantum happenings in your car, watch and computer.’
Most biologists think that quantum effects all just cancel out in the brain, that there’s no reason to think they’re harnessed in any way. Of course they’re there; quantum effects are there in your car, your watch, and your computer. But most things — most macroscopic objects — are, as it were, oblivious to quantum effects. They don’t amplify them; they don’t hinge on them. Roger thinks that the brain somehow exploits quantum effects…Daniel Dennett
We will now need to know why “quantum effects” don’t transfer — or apply — to the brain as a whole. Or, more specifically, we need to know why they don’t cause (or help bring about) mental phenomena or consciousness. That is, why is there such a sharp dividing line between the micro (Dennett’s “quantum effects”) and the macro (the brain or mind/consciousness)? Surely there can’t be such a neat and tiny cutoff point between these two worlds. (Then again, it’s not logically absurd to argue that there is indeed such a cutoff point.)
Sure, there are quantum happenings in the brain or neurons. Then again, there are quantum happenings in your car, watch and computer.
It’s true that in order for Dennett’s watch/car to be a watch/car, it doesn’t depend on the quantum effects which are occurring inside it. However, why should that also be true of the brain and its relation to mind/consciousness? The nature and functioning of a car/watch is very different to the reality and functioning of the brain and mind/consciousness. A car/watch is oblivious to the quantum effects inside — though only if it isn’t treated qua car/watch! However, it’s of course the case that a car/watch can also be analysed as a medium of quantum effects (though not, again, qua car/watch). Then again, it is strictly true that a car/watch — qua car/watch! — doesn’t depend on quantum effects/events/conditions? Surely it does so in the simple sense that if there were no quantum effects/events/conditions, then there would be no car/watch either. And, yes, it’s true that this applies to literally all other natural objects — and artificial objects as well.
Despite all that, according to Penrose, quantum effects/events/conditions do indeed have an effect on the large scale. He makes that plain here:
The very existence of solid bodies, the strengths and physical properties of materials, the nature of chemistry, the colours of substances, the phenomena of freezing and boiling, the reliability of inheritance — these, and many other familiar properties, require the quantum theory for their explanations.Penrose
However, even though it’s true that these “solid bodies”, etc. may “require the quantum theory for their explanations”; that doesn’t also automatically mean that such quantum effects are in any way substantive. It simply means that quantum mechanics is a part of the whole picture. So, in the sense of supplying a complete picture of such “bodies” and “materials” — then, yes, of course quantum theory will be required.
Ironically enough, Dennett himself does accept that quantum events/effects/conditions/etc. influence (or affect) the large scale. He says that quantum mechanics is “stunningly successful at predicting and explaining many phenomena, including everyday phenomena such as the reflection and refraction of lights, and the operation of the proteins in our retinas that permit us to see.”
Of course it may still be the case that because
quantum mechanics can “predict and explain” (remember that Penrose also used the word “explanation”) such things as “the reflection and refraction of lights”
that this doesn’t also mean that
quantum mechanics has an (causal) impact on these things.
…. Then again, surely it does mean that!
And if all this is true of the aforementioned light and protein molecules, then why can’t it also be true of the brain and consciousness? Of course the parallels between
quantum mechanics and the reflection and refraction of light
quantum mechanics and the brain and mind/consciousness
may not be parallel (or equivalent) in every respect. However, surely that wouldn’t matter too much in this case. What matters is whether or not quantum mechanics is having an impact on the brain and therefore on the mind/consciousness. It doesn’t need to be the case that quantum mechanics does so in precisely the same way in which it impacts on (to use Penrose’s words again) “solid bodies, the strengths and physical properties of materials, the nature of chemistry, the colours of substances, the phenomena of freezing and boiling, the reliability of inheritance.”
To repeat: perhaps the quantum-mechanical explanations of these phenomena are at a different level to actually arguing that quantum-mechanical events actually bring about (or cause) such phenomena. Again, is there a difference between
quantum mechanics explaining consciousness
quantum-mechanical effects/events/states causing (or bringing about) consciousness?
Surely if quantum mechanics can explain the mind/consciousness, it can only do so because quantum-mechanical events/effects/conditions also bring about (or cause) the mind/consciousness.
Having said all that, it’s of course the case that Penrose is fully aware of the need to explain this micro-macro link. The following is just one example of him doing so:
For my picture, I need this quantum-level activity in the microtubules; the activity has to be a large-scale thing that goes not just from one microtubule to the next but from one nerve cell to the next, across large areas of the brain. We need some kind of coherent activity of a quantum nature which is weakly coupled to the computational activity that Hameroff argues is taking place along the microtubules.Penrose
So Penrose acknowledges the need to tie the quantum scale to the (to use Penrose’s own term) “large-scale”. Basically (as with Dennett’s car/watch), there are indeed quantum effects/events/conditions in microtubules — as there are in everything else. So how can we tie these microtubular quantum phenomena to the large-scale? That is, how can we tie them to nerves and indeed from “one nerve cell to the next, across larges areas of that brain”? In a sense, if quantum effects/events/conditions are happening at the level of microtubules, then (as stated) they must also be happening at the level of nerve cells and indeed across large areas of the brain. But, again, are these nerve cells or large areas of the brain in the same position as Dennett’s car/watch? (The one obvious difference is that the former are biological and the latter aren’t.)
In the quote above (at the least), Penrose doesn’t offer us an answer to these questions. The questions are simply raised. Indeed to use Penrose’s own words: “We need some kind of coherent activity of a quantum nature which is weakly coupled to the computational activity that [Stuart] Hameroff argues is taking place along the microtubules.”
In basic terms, the quantum effects/events/conditions which occur in individual microtubules need to be “coupled” with the quantum effects in other microtubules. This coupling, according to Penrose, is achieved through “quantum coherence” and “quantum superpositioning”. Clearly these ideas take us beyond neuroscience.
So isn’t all this mere speculation?
Whatever the case is, Penrose’s positions will require both quantum theory and neurobiological detail to stand their ground. That is, the quantum leap from the neurobiological quantum scale to the brain and mind/consciousness needs much quantum-theoretic, neurobiological and philosophical defense.