2009/5/3 Bruno Marchal <marchal.domain.name.hidden>:
> I think that if you take a real forest with birds, here and there, you
> can interpret some behavior as NAND or NOR, but you will not succeed
> ever in finding the computation of factorial(5).
But you can interpret *any* behaviour as a NAND gate, in an ad hoc
fashion. It doesn't even need to be consistent from moment. On a
Tuesday 3 birds landing could stand for "1" while on a Wednesday 3
birds landing could stand for "0", and on a Saturday it could stand
for "1" again. In this way you could take the physical activity
carried out by a store-bought computer calculating factorial(5) and
map it onto the forest with the birds. Of course, this won't give you
the answer to factorial(5) unless you already have the answer, but
that just means that the computation is obscured, in the same way a
message is obscured if encoded with a one-time pad that is
subsequently destroyed and forgotten. In fact, even with the
store-bought computer the computation is obscured if there are no
intelligent beings around who can understand it. So, if the
computation supervenes on the activity of the store-bought computer
without regard for whether any external observer is around to
understand, then it also supervenes on the activity of the forest with
the birds. Other possibilities are that the computation supervenes on
physical activity only when an external observer understands it (which
poses difficulties for a closed virtual reality with its own conscious
observers), or that the computation does not supervene on physical
activity at all.
--
Stathis Papaioannou
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Received on Sun May 03 2009 - 17:00:35 PDT