Physics, Soul and Consciousness

Sean M. Carroll at Scientific American argues that agnosticism about an immaterial soul and life after death is no longer justified in the light of modern science:

"Even if you don't believe that human beings are "simply" collections of atoms evolving and interacting according to rules laid down in the Standard Model of particle physics, most people would grudgingly admit that atoms are part of who we are. If it's really nothing but atoms and the known forces, there is clearly no way for the soul to survive death. Believing in life after death, to put it mildly, requires physics beyond the Standard Model. Most importantly, we need some way for that "new physics" to interact with the atoms that we do have.

Very roughly speaking, when most people think about an immaterial soul that persists after death, they have in mind some sort of blob of spirit energy that takes up residence near our brain, and drives around our body like a soccer mom driving an SUV. The questions are these: what form does that spirit energy take, and how does it interact with our ordinary atoms? Not only is new physics required, but dramatically new physics. Within QFT, there can't be a new collection of "spirit particles" and "spirit forces" that interact with our regular atoms, because we would have detected them in existing experiments. Ockham's razor is not on your side here, since you have to posit a completely new realm of reality obeying very different rules than the ones we know.

But let's say you do that. How is the spirit energy supposed to interact with us? Here is the equation that tells us how electrons behave in the everyday world:

Don't worry about the details; it's the fact that the equation exists that matters, not its particular form. It's the Dirac equation -- the two terms on the left are roughly the velocity of the electron and its inertia -- coupled to electromagnetism and gravity, the two terms on the right.

As far as every experiment ever done is concerned, this equation is the correct description of how electrons behave at everyday energies. It's not a complete description; we haven't included the weak nuclear force, or couplings to hypothetical particles like the Higgs boson. But that's okay, since those are only important at high energies and/or short distances, very far from the regime of relevance to the human brain.

If you believe in an immaterial soul that interacts with our bodies, you need to believe that this equation is not right, even at everyday energies. There needs to be a new term (at minimum) on the right, representing how the soul interacts with electrons. (If that term doesn't exist, electrons will just go on their way as if there weren't any soul at all, and then what's the point?) So any respectable scientist who took this idea seriously would be asking -- what form does that interaction take? Is it local in spacetime? Does the soul respect gauge invariance and Lorentz invariance? Does the soul have a Hamiltonian? Do the interactions preserve unitarity and conservation of information?"

As far as commonly prevalent notions of soul as substance dualism go, this is a pretty effective criticism. Substance dualism does struggle badly to retain credibility given all that we know about modern physics and neuroscience. But this is not the end of the story, because Sean Carroll ignores a very crucial part of the debate. The Standard Model of particle physics as yet cannot account for how consciousness is produced. It is true that in the light of what we know from neuroscience it is an almost certain scientific fact that consciousness is produced by the brain, and I have no intention of disputing that. However, it is far from clear how the brain produces consciousness. The Standard Model of particle physics offers no clues as to how consciousness can be generated in neuronal circuits from purely physical processes.

Yes, it would be rational for a scientist to hypothesize that the unknown mechanism of consciousness would turn out to be entirely consistent with current knowledge of modern science, but it is not something that we know for a fact. While Physicalism is a reasonable philosophical position to take for a scientist, it is by no means the only reasonable position to take. It is entirely possible that the basic constituents of matter possess non-physical properties that are precursors to phenomenal consciousness and which ultimately lead to the development of conscious awareness within neuronal circuits. This position is a variant of Panpsychism. Obviously, I do not know, nor I am in a position to hypothesize as to how these non-physical properties may be demonstrated and how these non-physical properties create consciousness. The matter is still at a very basic stage of philosophization, though ultimately I do believe the matter would be resolved by scientific means.

Either: The standard model of particle physics is complete and correct, and is consistent with the generation of consciousness is some as yet unknown way. (Physicalism)

Or: The standard model of particle physics is not complete, and there are as yet unknown non-physical properties of basic constituents of matter that are precursors to consciousness and ultimately lead to conscious awareness in neuronal circuits. (Panpsychism)

P.S. I do not think that panpsychism provides a sufficient basis for belief in an immaterial soul and life-after-death. I am afraid believers in these two are still going to struggle to explain how these beliefs can be justifiably maintained in the light of modern science.


Komal said…
" is an almost certain scientific fact that consciousness is produced by the brain"

Oh, it is not certain at all. The only thing that is certain is that conscious events correlate with neural events. But that consciousness is produced by the brain is not evident, and is something that only epiphenomenalists would accept.
Abdullah Khalid said…

Try this on for size...

Also, once we create a conscious AI, Panpsychism would certainly fail. Since, the same code running on any type of computer would result in the same AI..
Awais Aftab said…
@ Abdullah

I read that just a few days ago [h/t Luke]. Very good article. Plan to comment on it soon.

Regarding conscious AI, it is not at all entirely clear at the moment whether AI can ever have subjective awareness. [Searle's Chinese Room Argument] The matter is not settled. It would only be settled once a conscious AI is actually created. Even then, it would depend on whether we can elaborate the mechanisms by which consciousness can be generated from purely physical processes. If you a conscious AI and you have no idea what makes it conscious, then the physicalism vs panpsychism debate would still be on.
Awais Aftab said…
@ Komal

Ok, yeah, we have no direct evidence of production. But we have a very strong correlation, and we know that intact and functioning neurons are required for consciousness, and defects in neurons produce a corresponding defect in consciousness. And this happens to such a degree that if we separate the two hemispheres of the brain by incising the corpus callosum, preventing the exchange of information, we create two separate centers of consciousness, each with its own respective sensory information and motor and cognitive functions! The correlation is established to such a degree that the only likely scientific explanation is that the brain produces consciousness. I wouldn't be dogmatic as to say that this is the only rational and philosophical possibility, but for now this is the one that fits the scientific data best.
Komal said…
"The correlation is established to such a degree that the only likely scientific explanation is that the brain produces consciousness."

I don't see how. It is only one hypothesis, which is no more parsimonious, intelligible or plausible than that, for example, consciousness is being 'channeled' through the brain (or rather, whether it is depends on your background metaphysical assumptions, but it is not in light of the scientific data alone).

Personally, I don't know what the exact relationship is between consciousness and the brain, but I know that materialism and epiphenomenalism are false (I have reasons behind this position, but I won't go into it here).
Awais Aftab said…
@ Komal

I am not supporting materialism or epiphenomenalism either.

I accept I don't have a knock-down argument against the 'channel theory' for now. The channel theory seems vague and inadequate to me when it comes to specifics of neurophysiology. For instance, let's say we have a neurological deficit X that produces a corresponding deficit X in consciousness. So what exactly happens to the consciousness that is no longer being channelled through neurons that comprised the deficit? Does it cease to exist? If it doesn't, in what way does it continue to exist?

If you want a specific example, let's say Neglect Syndrome (
This occurs when a damage to right brain hemisphere will cause a person to neglect the left side of the visual field. The patient will behave as if the left side of the visual field doesn't even exist! The patient will not be conscious of the left visual space, nor will have insight into his own disease.

How would the 'channel theory' explain such a scenario? What is happening to the consciousness of the left side of visual field?
Anonymous said…
Dear Komal

You seriously need to start a blog....

Your Admirer
Abdullah Khalid said…
You missed my point. If the AI can run on ANY machine (or practically, on a large number of different architectures) that would essentially show that Panpsychism is incorrect..
Awais Aftab said…
@ Abdullah

Are you saying that a computer code will be able to create consciousness?
Komal said…

I suppose one could come up with theories, such as that there is some sort of general consciousness which takes in particular forms when channeled. Or something. Anyway, I have no stake in this, since I don't believe in channel theory :P.

Anonymous Admirer,

Thanks, lol. I used to have a blog, but it felt too self-indulgent, and too exposing, so I stopped. I also don't like the 'static' quality of blogs (the fact that written posts just hang there).