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mattnewport comments on The two insights of materialism - Less Wrong
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Do you mean the Church-Turing-Deutsch principle? It appears to me that Pearce at least in the linked article is making a claim which effectively denies that principle - his claim implies that physics is not computable.
Why? Pearce is a physicalist, not a computationalist; he ought to accept the possibility of a computation which is behaviorally identical to consciousness but has no conscious experience.
What sense of 'ought' are you using here? That seems like a very odd thing to believe to me. If you think that's what he actually believes you're going to have to point me to some evidence.
So that means you are a computationalist? Fine, but why do you think physicalism may be incoherent?
It's hard to fish for evidence in a single interview, but Pearce says:
To me, this reads as an express acknowledgement of the CT thesis (unless quantum gravity turns out to be uncomputable, in which case the CTT is just plain false).
The distinction seems to hinge on whether physics is computable. I suspect the Church-Turing-Deutsch principle is true and if it is then it is possible to simulate a human mind using a classical computer and that simulation would be conscious. If it is false however then it is possible that consciousness depends on some physical process that cannot be simulated in a computer. That seems to me to be what Pearce is claiming and that is not incoherent. If we live in such a universe however then it is not possible to simulate a human using a classical computer / universal Turing machine and so it is incoherent to claim that you could simulate a human but the simulation would not be conscious because you can't simulate a human.
I honestly don't see how you make that connection. It seems clear to me that Pearce is implying that consciousness depends on non-computable physical processes.
You seem to be begging the question: I suspect that we simply have different models of what the "problem of consciousness" is.
Regardless, physicalism seems to be the most parsimonious theory; computationalism implies that any physical system instantiates all conscious beings, which makes it a non-starter.
Say again? Why should I believe this to be the case?
Basically, the interpretation of a physical system as implementing a computation is subjective, and a sufficiently complex interpretation can interpret it as implementing any computation you want, or at least any up to the size of the physical system. AKA the "conscious rocks" or "joke interpretations" problem.
Paper by Chalmers criticizing this argument, citing defenses of it by Hilary Putnam and John Searle
Simpler presentation by Jaron Lanier
I can see why someone might think that, but surely the requirement that any interpretation be a homomorphism from the computation to the processes of the object would be strong restriction on the sets of computation that it is instantiating?
Intriguing. Could you elaborate? Apparently "homomorphism" is a very general term.
Having printed it out and read it, it seems that "any physical system instantiates all conscious beings" is fairly well refuted, and what is left reduces to the GLUT problem.
Thanks for the link.
I remember seeing the Chalmers paper before, but never reading far enough to understand his reasoning - I should probably print it out and see if I can understand it on paper.
Edit: Yes, I know that he's criticizing the argument - I'm just saying I got lost last time I tried to read it.
So do you think there is a meaningful difference between computationalism and physicalism if the Church-Turing-Deutsch principle is true? If so, what is it?
Basically, physicalism need not be substrate-independent. For instance, it could be that Pearce is right: subjective experience is implemented by a complex quantum state in the brain, and our qualia, intentionality and other features of subjective experience are directly mapped to the states of this quantum system. This would account for the illusion that our consciousness is "just" our brain, while dramatically simplifying the underlying ontology.
Is that a yes or a no? It seems to me that saying physicalism is not substrate-independent is equivalent to saying the Church-Turing-Deutsch principle is false. In other words, that a Turing machine cannot simulate every physical process. My question is whether you think there is a meaningful difference between physicalism and computationalism if the Church-Turing-Deutsch principle is true. There is obviously a difference if it is false.
Why would this be? Because of free will? Even if free will exists, just replace the input of free will with a randomness oracle and your Turing machine will still be simulating a conscious system, albeit perhaps a weird one.