On 2/16/2014 12:56 PM, David Nyman wrote:
On 16 February 2014 16:17, Bruno Marchal <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>> wrote:On 16 Feb 2014, at 15:32, David Nyman wrote:On 16 February 2014 09:39, Bruno Marchal <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>> wrote:<snip> From "thought cannot act on matter" we arrive at "thought cannot refer to matter", and well, this is almost the consequence of step 8, as it says that the notion of matter has nothing to do with a material reality. Then we can still refer to the moon, but we know it is a sort of collective lawful "hallucination", or more exactly a mean on a set of 3p well defined computation.Yes, at least it seems that thought cannot refer to the sort of matter of which it would be an epiphenomenon!<snip> It illustrates, perhaps better than step 8, the difficulty of wanting a primitive matter having a primitive ontological reality capable of singularizing a conscious person capable to refer to it. I have to think more about this.In effect, might step 8 be regarded as a reductio of the premise that the laws of matter to which we can refer and those of any putative ur-matter can be in any way coterminous? Under CTM, it is consistent to suppose that the observable laws of matter must derive from some principled notion of computation. At the outset we grant the assumption that such a notion of computation must ultimately be grounded in primitive physical activity. Accordingly, we propose a system of such physical activity that is initially acceptable as grounding some set of computational relations corresponding to a conscious subject and hence to the physical laws observable by such a subject. Then we show that we can systematically change the physical contingencies such that every last vestige of these relations is evacuated even while all relevant physical events continue to go through.
But I don't think we can show that. I think the attempt fails because in order to include all the counterfactuals would require that the relations all be removed to a complete separate world.
Brent
This in effect provides a reductio of the original premise, under CTM: That the observable physical laws can be supposed to derive directly from a more primitive physical activity and simultaneously from any principled notion of computation consistently extractable from such activity. Since both cannot be the case, we must opt for one or the other.However, one distinction between arithmetic / computation as an ontology, and some kind of putative ur-physics, is that it is more difficult to discern any principled motivation whatsoever to derive "reference" in a primitive physics. A typical response to this reference problem is to justify CTM by smuggling an ad hoc notion of computation into physics.Yes. That is why at first sight I took the discovery of the quantum universal machine as a blow for comp. I thought that the quantum formalism provided a notion of physical computability, but it brought only a notion of physical computation, which is not excluded with computationalism (it is a sort of direct exploitation of the statistical nature of the computations below our substitution level).Could you elaborate a little on the distinction you see between physical computability and physical computation?It is ad hoc in the sense that "physical computation" is still no more than primitive physics, so now computation itself becomes an epiphenomenon of physics and consciousness therefore an epiphenomenon of an epiphenomenon. If not a blatant contradiction, this strikes me as quite close to a reductio.It makes arithmetic an epiphenomenon of physics, and it makes physics an epiphenomenon of physics.Computation (as emulated in arithmetic) on the other hand offers, at least, a principled system of internally-recursive self-reference that could motivate the layers of connectivity between the ontological base and the level of indexical "physical reality".With a big price of "reducing" physics to a "unique" calculus of self-reference on the consistent, and/or "true", or both extensions. This makes sense only if the arithmetical or quasi-arithmetical []p & p, []p & <>t, (and []p & p & <>t) obeys knowledge and probability logic respectively, and that is the case when p is restricted on sigma_1 sentences (which emulates UD*). Bruno
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