I had a thought about an alternative way of expressing the UDA
(universal dovetailer argument).

Computationalism is the statement that "I am a computation". To use
the RITSIAR acronym, computations are real in the sense I am real. But
the Church-Turing thesis gives a particular model of a computation, it
is effectively defining a computation as something that there is a
Turing machine emulating. 

The universal dovetailer is a computation. Contained within its
execution trace, are the execution traces of all other programs,
including itself. If we are a program, we can be found inside a
universal dovetailer, which can be found within another UD (infinitely
many, in fact).

To say that there must be a physical computer on which the dovetailer
should run, is rather similar to saying there must be an ultimate
turtle upon which the world rests. The little old lady was right in
saying "its turtles all the way down". Of course it is also analogous
to saying there must be a prime mover to start the causal chain. If
God created the world, then it immediately poses the question "Who
created God".

Since it makes no difference in any observable respect whether we are
living in a computer simulation running on a bare substrate, as one
that is incidently computated as part of a universal dovetailer, or an
infinite chain of dovetailers, we really can make use of Laplace's
ripost to Napoleon "Sire, I have no need of that hypothesis" with
respect to a concrete computer running our world.

To rescue the primitive matter world, we need to deny the existence of
the universal dovetailer. But this denies the Church Turing thesis -
we have to say some computations exist (eg ourselves), but others
don't. To make computationalism compatible with primitive materialism
requires us to abandon the Church-Turing thesis and redefine what we
mean by computation.

Cheers

-- 

----------------------------------------------------------------------------
A/Prof Russell Standish                  Phone 0425 253119 (mobile)
Mathematics                              
UNSW SYDNEY 2052                         [EMAIL PROTECTED]
Australia                                http://www.hpcoders.com.au
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