Hi all. In order to access the article I am pretty sure you need to establish 
an account on physics World. It is free. I did it so long ago I had forgotten.
 
Bruno, I am not sure exactly what you mean by "the existence of the first 
person indeterminacy in arithmetic", but offhand it seems to me to depedn on a 
sort of idealism that I do not accept.
 
Incidentally, quantum decoherence is best seen as a sort of thermodynamic 
effect. There are quantum measurements that can be reversed. I can give some 
references if anyone wants.
 
John


 
 
Professor John Collier  
Philosophy, University of KwaZulu-Natal
Durban 4041 South Africa
T: +27 (31) 260 3248 / 260 2292
F: +27 (31) 260 3031
email: colli...@ukzn.ac.za>>> On 2012/06/01 at 02:45 PM, in message 
<cc50a53f-b07a-4c24-a602-d02c7c891...@ulb.ac.be>, Bruno Marchal 
<marc...@ulb.ac.be> wrote:

Hi John,

On 01 Jun 2012, at 13:02, John Collier wrote:

> http://physicsworld.com/cws/article/print/2012/may/31/the-quantum-game-of-life
>
> Sample excerpt:
> "Hopes that digital physics might be resurrected in some form rose in
> the early 1980s, when Richard Feynman proposed that the blatant gap
> between the power and information content of quantum theory and that
> of classical computers might be bridged by a new type of computer.
> His idea was born out of frustration at seeing classical computers
> take weeks to simulate quantum-physics experiments that happen faster
> than a blink of an eye. Intuitively, he felt that the job of
> simulating quantum systems could be done better by a computer that
> was itself a quantum system."

He was of course right on that. Actually I don't succeed in getting  
the paper from the link above.

About quantum information, here is an interesting talk by Ron Garrett,  
quite coherent with the (classical) computationalist theory of mind,  
on quantum information, seen as information theory on the complex  
numbers:

http://www.youtube.com/watch?v=dEaecUuEqfc

Personally I am not (yet?) entirely sure that quantum information is  
"just" classical information on the complex numbers, I think this is  
partially true, and theorem like Gleason theorem makes me believe that  
this is very plausible. Ron Garrett gives a pretty picture of Everett  
QM (QM without collapse). His account of measurement is rather  
illuminating (close to the work of Adami and Cerf).

Ron Garrett is information theoretic minded, and, with respect to  
computationalism (comp), has a coherent view of physics. Of course he  
does not seem aware of the necessity of such a view once we postulate  
comp, and the fact that this necessitates to take all computations  
(the one done below our classical comp substitution level) into  
account, (not just the quantum one) and to justify the quantum  
interferences from the first person perspective any self-justifying  
universal number.

Comp shows that the qubit ---> bit road (decoherence) is two sided.

Technically, due to diagonalization used to make the self-reference,  
you get the split between truth and justifiable, which provides a tool  
to distinguish the qualia and the quanta, as different but related  
mode of information, on the "inverse road" bit --> qubit.

I think Ron Garrett explains (very shortly but rightly ) the qubit ->  
bit justification. Comp provides a reverse of that justification, and  
this doubled by the communicable/non-communicable (G/G*) splitting:  
the  bit -> quantum-bit, and the bit -> quale-bit*,  with the  
explanation of the fact that the quale bit* can't be quantified nor  
described (provably so in the ideal case of arithmetically self- 
referentially correct machine)

Comp forces, just to remain coherent, to extend Everett's way of  
embedding the observer into the physical wave,  to his embedding in  
all arithmetical relations, by first person indeterminacy, with the  
advantage of explaining a fundamental role to the (universal) person  
points of view, and hopefully so, to justify QM or refuting comp, or  
weakening it or constraining it.

To be sure computationalism is incompatible with digital physics. If  
*we* are machine (classical or quantum) then neither the fundamental  
reality, nor its physical part, can be Turing emulable, despite  
quantum machine can be Turing emulated. This is more or less a direct  
consequence of the existence of the first person indeterminacy in  
arithmetic.

Bruno Marchal

http://iridia.ulb.ac.be/~marchal/



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