Could David Pearce explain his views on consciousness, materialism, and quantum physics in simple language?
1) Consciousness.
First-person facts are objectively real. From the experience of a beautiful sunset, to the sound of distant thunder, to an introspective thought-episode, all you ever know, except by inference and conjecture
, are the subjective contents of your own mind.
Compare this
expansive conception of consciousness with the narrow conception implicit in perceptual direct realism. Perceptual direct realists believe that while awake, they enjoy direct access to material objects in their mind-independent local surroundings.
In contrast to commonsense direct realism,
inferential realists about perception believe that e.g. the
empirical skull that you can feel right now with your
empirical hands differs from the theoretically-inferred
transcendental skull that encases your world-simulation. On occasion,
poets grasp the human predicament better than philosophers or scientists (“
The brain is wider than the sky…”). Perhaps see
Antti Revonsuo or
Steve Lehar for contemporary expositions of the world-simulation model of perception.
You can appreciate that your empirical and transcendental skulls are distinct when having a lucid dream. When lucid dreaming, you know that everything beyond your phenomenal mind and its world-simulation is theoretical – though no less real.
Contra perceptual direct realism, “waking up” doesn’t change this theoretically inferred status. “Waking up” does not confer direct access to physical reality that transcends your skull-bound virtual world. Rather, on waking from a dream, you may infer that the mind-independent external environment now partially
selects – not creates – the contents of your consciousness, including the phenomenal world-simulation run by your CNS.
Hard-nosed scientists sometimes dismissively say things like “What do you mean by ‘consciousness’?” Yet consciousness
isn’t something that is, by its very nature, subtle, elusive, and hard to define, as are your introspective thought-episodes and meta-cognitive self-awareness. Other examples of consciousness include the medium-sized dry objects populating your everyday world-simulation – the chairs and tables and coffee-mugs that one normally thinks of as exemplifying the physical. And solid
rocks.
Note that the world-simulation model of perception
isn’t a sceptical or a solipsistic view. Nor does the world-simulation model of perceptual experience commit us to any sort of idealist ontology, although non-materialist
physicalismis the option I tentatively favour. Rather, evolution over millions of years via natural selection has thrown up countless skull-bound world-simulations besides one’s own. These macroscopic world-simulations are each centred on a different body-image. Selfish DNA ensures that all of us conceive ourselves to be the centre of our own world. Other body-images play walk-on parts. Virtual universes die with the minds that run them.
For around a tenth your life, your world-simulation is psychotic (“dreaming”). For another fifth or so of your life, you are dreamlessly asleep, a phenomenally-unbound pack of effectively classical neurons. But for around fourteen hours a day, your skull-bound mind runs a seemingly law-governed virtual world. This robustly classical-seeming world-simulation tends to track genetic fitness-relevant features of your local environment, not least the state of your extra-cranial body. This inferred – but not directly perceived – environment may be described by an approximation of classical physics, and more accurately by quantum field theory (
QFT), our best mathematico-physical description of the universe. In my view, quantum field theory also explains the properties of our minds and their macroscopic world-simulations.
Yet how are our conscious minds physically possible, given what we think we know about the fundamental properties of matter and energy?
2) Materialism versus physicalism.
The triumph of the
Standard Model suggests the world can exhaustively be described by the equations of mathematical physics.
Physicalism is true. With two big complications, no “element of reality” is lacking of from the formalism of quantum field theory, or more strictly, its M-theoretic extension.
And the two complications?
First, consciousness. Why aren’t we
p-zombies?
Second, the intrinsic nature of the physical. We don’t know what “breathes fire into” the equations of physics and makes a universe for them to describe. Stephen Hawking doesn’t know. Ed Witten doesn’t know.
Despite our ignorance, “materialist” physicalists make a seemingly modest metaphysical assumption. The unknown essence of the physical is non-experiential. Quantum field theory is about fields of insentience. It’s an intuitionI share.
Why not trust such an intuition?
Well, if “materialist” physicalism is true, then we face the Hard Problem of consciousness. The Hard Problem is a rather grand way of saying that materialism is inconsistent with the empirical evidence. I am not a p-zombie. I suspect that you aren’t either.
Faced with the empirical refutation of our best-developed story of reality, some scientifically-minded philosophers and philosophically-minded scientists go into denial and lose their minds, figuratively at any rate (
cf.
Are radical eliminativists about consciousness p-zombies?). Other folk intellectually despair and turn to dualism or mysterianism. Some philosophers invoke “complexity”, but tacitly accept what philosophers call “
strong” emergence. The reality of strong emergence would spell an end to the ontological unity of science. Imagine, fancifully, that molecular biology had proved irreducible to physics. If lawless ontological eruptions into the fabric of reality are real, then New Agers and religious believers can rejoice. Physicalism is the god that failed.
Or has it?
Non-materialist physicalism simply drops the metaphysical assumption. You are made up of exactly the same
subjective field-theoretic stuff as the rest of the universe. By contrast, fields of
insentience are on a par with fields of luminiferous aether.
Perhaps also compare non-materialist physicalism with traditional forms of
panpsychism and pre-scientific animism. Traditional panpsychists recognise the existence of physical properties as normally understood. But panpsychists also believe that experience is attached to, or associated with, these physical properties in some fundamental way. By contrast, non-materialist physicalism doesn’t claim that consciousness is inseparably associated with the world’s fundamental fermionic and bosonic fields. Rather, non-materialist physicalism proposes that fermionic and bosonic fields
are fields of consciousness. “P-zombies” are impossible because they are
unphysical.
According to non-materialist physicalism, what makes biological minds so unusual is how our consciousness is phenomenally bound into macroscopic world-simulations,
not the existence of subjective experience
per se. For subjective experience
is the essence of the physical. Only the physical can have causal efficacy. If consciousness
weren’t the essence of the physical, then consciousness would lack the
causal power to talk about its own existence, as we’re doing here
. Without phenomenal
binding, however, you are no more a unitary subject of experience than a rock or a lettuce or a Mexican wave – or a classical digital computer.
So how is
phenomenal binding physically possible?
On the face of it, neither classical nor quantum physics can explain how a pack of biological nerve cells can support feature-bound phenomenal objects, for example live cats, i.e. “local” binding, or perceptual unity, i.e. “global” binding, embracing the unity of perception and the unity of the self. If physicalism is true, then why aren’t you at most just 86 billion discrete pixels of micro-experience – what American psychologist and physician William James christened “mind-dust”? Phenomenally-bound virtual world-making should be impossible for a bunch of decohered, membrane-bound neurons. Granted, probes of the central nervous system disclose tantalising
hints of a structural match between mind and brain. Thus when you see e.g. a live cat, neuroscanning can identify neuronal edge-detectors, motion-detectors, colour-mediating neurons (etc)
synchronously firing. But neuroscanning reveals no cat, nor even the formal structural shadow of cat. Membrane-bound “pixels” of experience are just aggregates of Jamesian mind-dust. What David Chalmers calls the “structural mismatch” between your experience and the microstructure of your CNS seems unbridgeable.
“Naturalistic” dualism beckons.
But let’s not surrender yet…
3) Quantum physics, definite outcomes, and phenomenal binding.
As far as we know, the
formalism of quantum mechanics is complete.
Experiment faithfully matches theory. The superposition principle of QM has universal validity. Neither consciousness not anything else “collapses the wavefunction”, i.e. the ostensibly non-unitary transformation of the state vector into a single definite state upon measurement. The big mystery is
definite outcomes. Why do you see a live cat, or a dead cat? The normally sober expert on the foundations of quantum theory,
Maximilian Schlosshauer, is worth quoting here. Schlosshauer notes how the problem of definite outcomes is “
a dire warning something is irrevocably rotten at the core of quantum mechanics, something that could prompt this theoretical edifice to collapse at any moment, like a house haphazardly erected on swampy grounds.”
Some physicists are brave (or IMO foolhardy) enough to
tamper with the
unitary Schrödinger dynamics. I’m conservative on that score. My response to the measurement problem nonetheless sounds like schizophrenic word-salad. Recall Schrödinger’s “
infernal device”.
Neither before, during, or after opening the chamber do you perceive a definite classical outcome. Nor are there decohered (“split”) Everett branches where you perceive a definite classical outcome. Ever. Anywhere. Definite outcomes don’t exist, only coherent neuronal superpositions
subjectively experienced as definite classical outcomes. Real definite outcomes would create information
ex nihilo. A
cardinal principleof quantum physics is that information can never be created or destroyed. More speculatively, a zero ontology suggests the information content of reality itself is
nil.
On the face of it, the claim that definite outcomes are fiction is nonsense. You observe live cats. You observe dead cats. You never observe superposed live-and-dead cats. What else could a “definite outcome” mean?
Yet recall our discussion of perceptual consciousness
(1) above. “Observations” are just one kind of subjective experience internal to your skull-bound virtual reality. On my view, only the universal validity of the superposition principle allows biological minds to undergo the fitness-enhancing experience of classicality. If, counterfactually, perceptual direct realism were true, then the superposition principle would indeed demonstrably break down whenever a measurement or observation is made. See the
Born rule. But perceptual direct realism is false. Your mind is running a world-simulation. And only the superposition principle allows you to undergo the coherent phenomenally-bound superpositions of neuronal feature-processors subjectively experienced as a classical live cat or a classical dead cat. Superpositions are
individualphysical states, not classical aggregates or mixtures. Environmentally-induced
decoherence explains how neuronal superpositions progressively become unbound – fast.
Again, this proposal is intuitively insane. Theoretical physicists, notably
Max Tegmark, have done the maths. Thermally-induced decoherence alone is stupendously powerful. The effective lifetime of “cat states” in your warm and wet CNS can be calculated. It’s femtoseconds or less. Even if superpositions
areexperienced, “cat states” in your CNS must at most be psychotic noise.
Even ifnon-materialist physicalism is true, psychotic noise is computationally useless. Performing interferometry experiments to test this assertion would be as pointless as using interferometry to investigate whether the superposition principle breaks down in the central processing unit of your PC. No, it doesn’t; but your PC functions as a classical Turing machine. Likewise, your waking world-simulation seems well-ordered, law-governed, effectively classical. You are
not a universal quantum computer.
Indeed. So why not treat sub-femtosecond decoherence times as a
reductio ad absurdum of quantum mind – or at least, a
reductio of theoretically-conservative (“no collapse”) quantum mind
proposals that don’t invoke any new principle of physics like the Penrose-Hameroff
Orch-OR theory? Sure, if coherent superpositions of distributed neuronal feature-processors in the CNS endured for
milliseconds, then we’d have a credible candidate for a perfect structural match between our phenomenally bound minds and the architecture of the CNS, and hence ultimately physics. Two disparate kinds of holism, a single elegant explanation.
Voilà! But the numbers don’t add up. The respective lifetimes of neuronal superpositions and our mental states aren’t even close. Femtoseconds versus milliseconds: it’s a different ballpark.
Enter
Quantum Darwinism.
“Quantum Darwinism” sounds like quantum healing and quantum tarot. It’s not. Quantum Darwinism is the name that theoretical physicists give to the selection mechanism that explains the emergence of
observer-independentquasi-classicality from quantum reality. The best non-technical account I know is John Campbell’s “Quantum Darwinism as a Darwinian process”:
https://arxiv.org/ftp/arxiv/pape....
But Wojciech Zurek himself is well worth reading, e.g. “Quantum Darwinism”:
https://arxiv.org/pdf/0903.5082v....
Together with
H-Dieter Zeh, Zurek is one of the pioneers of the decoherence program in
post-Everett quantum mechanics.
What happens when the selection mechanism of quantum Darwinism plays out inside your head? On the temporally coarse-grained scale of milliseconds captured by today’s neuroscanning, yes, dynamically stable quasi-classical neurons emerge from bedrock quantum reality. But at temporal resolutions of picoseconds, femtoseconds and attoseconds? Will the non-classical interference signature reveal functionless “noise”, or a perfect structural match between phenomenology and physics?
I don’t know. I hope experiment will tell us. See
Schrödinger’s Neurons?Evolutionary biologist Theodosius Dobzhansky once observed, "Nothing in biology makes sense except in the light of evolution". Maybe nothing in any true biological science of mind will make sense except in the light of quantum Darwinism in the CNS.
The experimental signature we’re looking for is subtle (
cf.
Double-slit experiment - Wikipedia), but not because the empirical evidence for quantum mind is subtle. Rather, in my view, the evidence that our minds are quantum minds consists in the phenomenally bound
classical-seeming world-simulation that you’re undergoing right now. The superposition principle creates the illusion of definite outcomes. A classical mind couldn’t phenomenally simulate a classical extra-cranial world. Phenomenal binding is classically impossible. But of course this is a philosophical argument, not a novel prediction (
cf.
Quantum computing: the first 540 million years). A good experiment needs to convince critics. And only a genuinely novel empirical prediction – in this case, a telltale non-classical interference signature that implicates
precisely the feature-processing neurons that neuroscanning identifies with any given phenomenally bound perceptual experience. If synchrony is really superposition, then the non-classical interference signature will tell us.
[
I’ve just read my reply. It’s not as simply worded as I’d like. Sorry. I’ve added some hotlinks. To stress: this is a conjecture I’d like to see experimentally falsified, not a declaration of belief. Most scientifically educated people who appreciate the power of decoherence will reckon a “Schrödinger's neurons” conjecture too insane to be seriously worth testing. Maybe they are right. I am just curious.]
