Re: Dreaming On

From: Bruno Marchal <>
Date: Wed, 2 Sep 2009 10:08:37 +0200

On 02 Sep 2009, at 03:17, Brent Meeker wrote:

> But only by isolating a bit of computation from the rest of universe.
> And it doesn't show that a computation supervenes on zero physical
> activity. And even if it did show that, it would not follow that
> mental
> computation *does* supervene on computation realized in Platonia with
> zero physical activity.

Maudlin's Olympia shows that a computation can be realized with zero
*computational* physical activity, and this means that if we keep
associating the consciousness to the computation, the physical
activity has no role there.
MGA shows that if we associate consciousness to the physical activity
implementing a computation, then we have to associate that
consciousness "in real time" to a description of that computation,
which can be seen as absurd in different ways.
We can come back on this, but I think it is better I explain what
mathematician means by computations.

MGA and MGA-like argument can be seen as an extension of what is done
in UDA1-6. It shows that a universal machine cannot see the difference
between "real", "virtual" and then "arithmetical". But like the notion
of virtual emulation has to be grasped for the step 6, the notion of
arithmetical computation has to be grasped before, and that is why I
am explaining the mathematician definition of universal machine and
its computations.

>> This is an absurd conclusion, so the hypothesis that motivates it -
>> i.e. CTM+PM - is thus shown to be contradictory and must be
>> abandoned,
>> not merely in this case, but in general: i.e. the exception has
>> broken
>> the rule. This is forced unless you can show where the logic goes
>> wrong.
> No, even if the conclusion is wrong that only shows that *some* step
> in
> the argument is wrong NOT that the conjunction of the computationalist
> theory of mind and primary matter is self contradictory.

You can say this for any proof by reduction ad absurdo. But if someone
pretend having done a reduction of absurdo of A+B, that is, pretend to
have provide a proof, or argument, that A+B -> false, then if you
disagree that this leads to ~(A+B), you have to *find* at which step
the error is. That's the very idea of proving. Of course in a
difficult "applied" subject, you can always find some loophole of the
kind "invisible horses driving cars", and it is a matter of pedagogy
to explains things spirit, instead of big set of formalities capable
of satisfying everyone in the first strike.
In the present case, you can always develop a sufficiently ridiculous
notion of matter and physical computation to block the proof, but it
should be clear that a strong change of the meaning of the hypothesis
is done.

> I don't even
> see where the argument uses PM to reach its conclusion.

Note that "PM" is used in all UDA1-7, and at that stage, you can still
argue that the supposedly existing physical universe is too little to
run a big part of the UD, (but we have already the result that comp
entails indeterminacy and non-locality). The step 08 just shows that
the move toward a "little physical universe" does not really work, in
the sense that the physical supervenience thesis, in the comp frame,
entails that we can show the physical activity non relevant with
respect to the computation. You have to believe that consciousness "in
real time" is related to static description of such computation, which
is perhaps not contradictory, but is non sensical. You can no more say
yes to the doctor 'qua computatio'.

> Maybe CTM+UD is
> a simpler explanation of the world, a return to Platonic idealism,
> but I
> don't see that its contrary is contrdictory.

It is contradictory with the idea that consciousness is related to
both the computation and the physical activity, in the PM sense of
physical activity. A movie of a brain become conscious qua computation
and without computation. It is not a mathematical contradiction, but a
conceptual difficulty preventing saying "yes to the doctor" by
appealing to the notion of computation. Like invisible horses pulling
cars could throw doubt to the thermodynamical explanation of car
motor. As I have always said, MGA does not eliminate completely some
use of Occam; it minimizes it, but, like always in applied math, you
can imagine a sufficiently bizarre notion of physical computation to
stuck the logic of the applied proof, a bit like your own move of
associating your consciousness to a non computable physical object
outside your brain. But with the generalized brain, this is taking
into account. If your consciousness, to exist, needs that uncomputable
object, you are no more in the comp frame.
It is like the collapse of the wave packet. It shows that the many-
worlds does not follow logically from the SWE, and the collapse is so
badly defined, that you can hardy evacuate it (like the God-of-the-gap
in physics), yet, I do think that the many-words follows directly from
the SWE, because the collapse is just that, an ad hoc construction,
undefinable in the theory, introduced to keep the consequence under
the rug.


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Received on Wed Sep 02 2009 - 10:08:37 PDT

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