Le 25-juil.-12, à 08:37, Russell Standish a écrit :

On Sun, Jul 22, 2012 at 02:41:29PM -0400, Stephen P. King wrote:
On 7/22/2012 7:13 AM, Bruno Marchal wrote:

Usually I restrict "substance" for physicalist primitive ontology,
like atoms, particles or strings, which does not exist primitively
in the comp theory, but should be derived (by the conclusion of
the UDA).

(Sorry for replying to Stephen's post - I can't respond to Bruno's
directly because of his non-standard email client)

Actually, this is a useful clarification, as it is a point that has
confused me.

So paraphrasing in my words, what Bruno is saying is:

"primitive" = ontological basis of reality ("urstuff" as I put it)
"matter" = atoms, particles, strings that appear in physical theory

COMP entails matter is not primitive means that the physical things we observe
(atoms, electrons etc) must be emergent phenomena from whatever the
urstuff really is. I have little problem with this statement, as it is
fairly clear that atoms are emergent constructs, and one suspects
things like electrons, or even strings might be too. Perhaps knots or
some other topological defects of space-time (which is itself an
emergent phenomenon of relationships between events).

Of course, COMP includes the arithmetic realism proposition. Bruno
claims this is just a statment of the truth of arithmetical statement
independent of what you or I think, ie that it is not an ontological commitment.

But another way of saying it is that it _is_ an ontological
commitment. The urstuff is the natural numbers.

OK. But nothing is made of numbers, so "urstuff" can be misleading.

In fact I think COMP is saying something rather more important. It
doesn't matter what the urstuff is, so long as it supports universal
computation. Physical phenomena must be derivable from the first
person account, and it is useless to speculate on the nature of
urstuff beyond its capability to support universal computation.

OK. But to derive physics, we have to postulate a least one (Turing) universal (Sigma_1 complete) reality, and derive physics from it.

Thinking about David Deutsch's point further, and the observation that
we don't see hypercomputation like the infinity hotel, we can say what
the urstuff is not - it is not a hypercomputer like the infinity
hotel, for instance, but we can't say which of the many equivalent
structures supporting universal computation it is.

Yes. The infinite hostel are recovered from inside arithmetic, which is far bigger than the outside view of it. It is a Skolem like situation. Note that this Skolem like situation makes the ultimate cardinality of reality absolutely undecidable. It is enumerable or bigger, but if we are machine we cannot distinguish a non enumerable third person ontological reality from an enumerable one. The first person reality, on the contrary, goes beyond all definable cardinals.



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