Le 29-août-06, à 13:14, Stathis Papaioannou a écrit :

> I'm not necessarily talking about every possible computation being 
> implemented by
> every physical system, just (at least) the subset of finite 
> computations implemented by
> a physical computer or brain. I think this is another way of saying 
> that a recording, or
> a single trace of a computation branching in the multiverse, can be 
> conscious. To prevent
> a recording being consious yoiu can insist on counterfactual 
> behaviour, but that seems an
> ad hoc requirement introduced simply to prevent the "trivial" case of 
> a recording or any
> physical system implementing a computation.

I think Maudlin's reasoning (better than the movie graph actually) 
shows exactly that. What Maudlin shows is that you can have some 
"recording" of a computation, and thus it does not handle the 
counterfactuals, but which can be made handling correctly the 
counterfactuals by adding pieces of inert matter, having no 
comp-genuine physical activity at all.
So the counterfactual correctness demand can be provided without adding 
*any* physical activity.
So, for a physicalist, counterfactual should be a red herring 'even 
with the quantum MWI (but as Russell points out, this is slightly more 
difficult to show).
For a computationalist, this means the entire "physical activity" is a 
red herring. The only counterfactuals which play a role are those 
corresponding to the mathematical structure of the computations. The 
physical emerges from the computational structure, which is entirely 
define by the number theoretical relation which are true independently 
of any physical considerations.

More technical remark: Counterfactuality is a very difficult notion. It 
is certainly one of the philosophical notion where logic (as a field of 
math) can help. The best work has been done by logician like David 
Lewis (notably in his book "counterfactuals") and Stalnaker. Now the 
quantum logician Hardegree has shown that, at least formally, Quantum 
Logic (QL) can be seen as a logic of counterfactuals. QL gives a 
genuine notion of proximity among "worlds" capable of providing truth 
value for counterfactual statements. This shows that the movie graph or 
OLYMPIA can be used for providing a shortcut between comp and the 
quantum. Alas, the movie graph and/or Olympia thought experiment is far 
subtler than the UDA (at least the seven first steps), and I am not 
following that road. The counterfactual logic and QL necessary for a 
minimal notion of comp-causality is provided by the G and G* variants 
Bp & Dp (corresponding to the "intelligible matter" secondary hypostase 
in Plotinus, and Bp & Dp & p (corresponding to sensible matter) in the 
lobian interview.



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