On Tue, Jun 14, 2005 at 04:39:57PM +0200, Bruno Marchal wrote:
> 
> 
> OK but it can be misleading (especially in advanced stuff!). neither a 
> program, nor a machine nor a body nor a brain can think. A person can 
> think, and manifest eself (I follow Patrick for the pronouns) through a 
> program, or a machine or a brain, ....

Actually, I think I was the one introducing these 3rd person neutral
pronouns (e, er & em). I picked up the habit from Michael Spivak
(well known mathematician).

Doesn't this beg the question a bit as to what a "person" really is?
In loose everyday conversation, a person is a member of the species
homo sapiens. However, surely we don't want to rule out the
possibility of other conscious things before we even start. And also
as you mention below, there are odd corner cases - the sleeping human
being etc.


> In some reasoning it is like cutting the hair, but once we tackle more 
> subtle questions it is important to make the distinction, imo.
> 

I agree - it has its place. I'm also notoriously impatient when it
comes to nailing down every last nuance, being more physicist than
mathematician. 

> 
> > Church-Turing thesis and arithmetical platonism (my all
> >description strings condition fulfills a similar role to arithmetical
> >platonism) are enough.
> 
> 
> I am not so sure. You are not always clear if the strings describe the 
> equivalent of a program (be it an universal program or not), or 
> describes a computations (be it finite or infinite). 

Both actually. One can feed a description into the input tape of a
UTM, hence it becomes a program. They may also be generated by a
program running on a machine.

> Consciousness 
> eventually is related to bunch of (sheaves of) infinite computations. 
> they can be coded by infinite strings, but they are not programs.
> 

Is this  because they are ultimately not computable (due to the
inherent indeterminism)?

> 
> >Furthermore, if the conscious program _is_ a
> >UTM in its own right, it can run on itself (actually this is pretty
> >much what my reading of what the Church-Turing thesis is).
> 
> I am not sure I understand this.
> 

Lets assume we have a UTM U, and a program A capable of consciousness
when run on U as U(Ax) = UoA(x), where x refers to arbitrary
additional input. Furthermore suppose UoA is also a UTM (o is compose
operator), so lets rewrite A in terms of the primitives of UoA, and
call it B. Hence UoA = UoAoB = UoAoBoB = etc.

My reading of the Church-Turing thesis is that universal computation
captures all possible forms of computation capable of being performed
by a human (and by obvious extension a conscious
"person"). Consequently conscious "people" are capable of universal
computation. 

There are various strengthenings of the CT thesis which are far from
obvious, and even false in some cases. One of my criticisms of your
work is that I'm not sure you aren't using one of the strong CT
theses, but we can come back to that.

> 
> >This obviates
> >having to fix the UTM. Perhaps this is the route into the anthropic
> >principle.
> 
> 
> ? Church's thesis just say things does not depend on which UTM you 
> choose initially 

All programs need to be interpreted with respect to a particular
machine. The machine can be changed by appeal to universal
computation, but then the program needs to be translated as well. But
then, I'm sure you know all this.

> 
> >
> >Finally, there is the possibility that a concrete observer (the
> >noumenon) exists somewhere, and that "conscious descriptions" are
> >merely the anthropic "shadow" of the observer being observed by itself.
> 
> 
> Again this is to fuzzy for me. I can agree and I can disagree.
> 

With COMP, I'm sure you disagree. Chapter 4 of your thesis directly
argues against this possibility. I don't really agree with it either,
but cannot rule it out once COMP is relaxed.

> I was 
> just saying that we say with "a machine can think " it is an abuse of 
> language for "the person associate to that machine is thinking".
> 
> Bruno
> 

Are you saying that it is an abuse of the language to say that my
observer maps O(x) can think? In which case I'd agree with you (and I
have never made that particular language abuse that I can recall). 

However, I consider human beings to be machines of a particular kind,
and I do consider human beings to think. Of course "machine" in this
case has only a rather loose connection to the machine of theoretical
computer science (the abstract Turing machine).

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