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 8 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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