Le 28-août-06, à 07:42, Stathis Papaioannou a écrit :

> Bruno marchal writes:
>> Le 26-août-06, à 16:35, 1Z a écrit :
>>>> And since the computer may be built and programmed in an arbitrarily
>>>> complex way, because any physical
>>>> system can be mapped onto any computation with the appropriate
>>>> mapping rules,
>>> That is not a fact.
>> It would make sense, indeed, only if the map is computable, and in 
>> this
>> case I agree it has not been proved. Again UDA makes such question non
>> relevant, given that the physical is secondary with respect to the
>> intelligible.
> Any computation that can be implemented on a physical system A can be 
> mapped
> onto another physical system B, even if B has fewer distinct states 
> than A, since
> states can be "reused" for parallel processing. If B is some boring 
> sysstem such as
> the ticking of a clock then the "work" (not sure what the best word to 
> use here is)
> of implementing the computation lies in the mapping rules, not in the 
> physical
> activity. The mapping rules are not actually "implemented": they can 
> exist written
> on a piece of paper

Honestly I am not sure about that.

> so that an external observer can refer to them and see what
> the computer is up to, or potentially interact with it. And if the 
> computer is conscious
> because someone can potentially talk to it using the piece of paper, 
> ther is no reason
> why it should not also be conscious when the piece of paper is 
> destroyed, or everyone
> who understands the code on the piece of paper dies. In the limiting 
> case, the platonic
> existence of the mapping rule contains all of the computation and the 
> physical activity
> is irrelevant - arriving at the same position you do.

OK, in the case the mapping rule can be coded in a finite way.
For example I can code the computation of any partial recursive 
function by using a n-body problem. But a slight change in the initial 
position of one of the body would destroy the information, and it is 
not clear why some other *finite* working mapping rule would appear, 
even in Platonia. Computation is a much constrained notion than people 
usually realize. You may be right, but I have never seen any proof. The 
probable reason for this is that such a proof would need a much more 
formal approach to physics, including what happens in the bottom, but 
nobody knows what happens there, and current theories makes big 
simplification there (renormalization, etc.).
I think that what you say is not totally excluded by string theory, but 
would be false with loop gravity, for example (in loop gravity 
everything is quantized, and I can build, if only by diagonalization, 
computation non mappable to any finite piece of loop-gravity-matter (if 
I can say).



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