David Nyman wrote:
> On 19 Aug, 00:20, Bruno Marchal <marc...@ulb.ac.be> wrote:
>> Note that I have never said that matter does not exist. I have no  
>> doubt it exists. I am just saying that matter cannot be primitive,  
>> assuming comp. Matter is more or less the border of the ignorance of  
>> universal machines (to be short). There is a fundamental physics which  
>> capture the invariant for all possible universal machine observation,  
>> and the rest is geography-history. Assuming comp the consistent-
>> contingent obeys laws.
> AFAICS the essence of Bruno's dispute with Peter consists in:
> 1)  ***If you accept the computational theory of mind (CTM)*** then
> matter can no longer be primitive to your explanations of appearances
> of any kind, mental or physical.
> 2) ***If you assert that matter is primitive to your explanation of
> appearances of any kind, mental or physical (PM)*** it is illegitimate
> to appeal to CTM.
> Bruno's position is that only one of the above can be true (i.e. CTM
> and PM are incompatible) as shown by UDA-8 (MGA/Olympia).   I've also
> argued this, in a somewhat different form.  Peter's position I think
> is that 1) and 2) are both false (or in any case that CTM and PM are
> compatible).  Hence the validity of UDA-8 - in its strongest form -
> seems central to the current dispute, since it is essentially this
> argument that motivates the appeal to arithmetical realism, the topic
> currently generating so much heat.  UDA-8 sets out to be provable or
> disprovable on purely logical grounds.  I for one am unclear on what
> basis it could be attacked as invalid.  Can anyone show strong grounds
> for this?
> David

I think you are right that the MGA is at the crux.  But I don't know whether to 
regard it 
as proving that computation need not be physically instantiated or as a 
reductio against 
the "yes doctor" hypothesis.  Saying yes to the doctor seems very 
straightforward when you 
just think about the doctor replacing physical elements of your brain with 
similar elements made of silicon or straw or whatever.  But then I reflect that 
I, with my 
new head full of straw, must still interact with the world.  So I have not been 
reduced to 
computation unless the part of the world I interact with is also replaced by 
elements (I think this problem is swept under the rug with the phrase "at the 
level of substitution").  So suppose the doctor also emulates all the world 
that I will 
ever interact with.  Now it is not so clear that such an emulation is 
computable, but 
suppose it is.  Now my consciousness is entirely emulation - but it is also 
entirely in 
another, emulated, world.  In that world it is physically instantiated.  So it 
has not 
been shown that the emulation can be uninstantiated mathematics.


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