Bruno,
There is clearly a qualitative difference between a minimal physical universe implementing every computation and *no* physical universe implementing every computation. I would like to think that the latter is the case, because it is simpler, less arbitrary, and I sort of have a feeling that it is the case... but you seem to take it is as a premiss, and I can't quite see where that comes from. To quote from your previous post:
"So comp + physical supervenience (phys-sup) would force
us to associate any consciousness experience to any physical processes.
And that would kill comp! So sup-phys -> NOT comp, or equivalently comp
-> NOT sup-phys."
Well, why would it kill comp? We would need to adjust to a view of the relationship between the physical and the mental as one->many rather than the more commonly understood one->one or many->one (the latter a consequence of functionalism), but we could still say that matter is necessary for computation and computation gives rise to consciousness, couldn't we?
A one->many mapping from physical state to computation will not work for a practical computer, and I think this is what you are referring to when you say that it is not true that a piece of matter implements all possible computations. In a practical computer, although we might arbitrarily map a physical state to a computational state, we cannot simultaneously map a physical state to more than one computational state, or we end up with a random mess. Hence, the number of possible physical states in a system puts an upper boundary on the number of possible practical computational states.
It might seem that the number of possible conscious computations that can be implemented on a physical system will be smaller than the number of all possible practical computations, but perhaps surprisingly this is not so: there are potentially vastly more conscious computations than there are possible physical states in the system. The reason for this lies in the 1st person/ 3rd person distinction that arises when we consider consciousness, allowing massive parallelism. Consider a limited, closed physical system running through a series of physical states over a one second period. Suppose this system "uses up" all its states calculating "2+3=5". Maybe it *could* have calculated "4+3=7" under a different interpretation or mapping of the same physical changes over the same time period, but it would have been meaningless to say that it could have done both simultaneously unless extra bits were available to separate the two calculations. But no such problem exists for the conscious calculation. Under one mapping, the physical system implements a program which thinks, "I am now experiencing my first second of life". Under a different mapping, it implements a program which thinks, "I am now experiencing my second second of life". These two programs link together to constitute two seconds of continuous conscious experience, for the simple reason that any such two programs implemented anywhere or anytime would be experienced as a linked sequence, with no subjective interruption or indication that anything unusual had happened. And that's just a start: all possible conscious programs are implemented simultaneously and unlike the calculations, do not need external interpretation, do not interfere with each other, and link up as appropriate due to their internal information content.
Stathis Papaioannou
----------------------------------------
> From: marchal.domain.name.hidden
> Subject: Re: computationalism and supervenience
> Date: Tue, 5 Sep 2006 12:22:04 +0200
> To: everything-list.domain.name.hidden
>
>
>
> Le 04-sept.-06, à 06:30, Stathis Papaioannou a écrit :
>
> > It is the association of any conscious experience with any physical
> > process
> > which links the Putnam/Searle/Chalmers/Egan/Mallah/Moravec (and me, and
> > probably many others independently) argument with the Maudlin/Marchal
> > argument. There are at least three, not just two, ways to explain the
> > problem:
>
>
> I agree and see your point (I think) but it remains pedagogically
> troubling to associate the two types of problems. Hal Finney did make
> also such a mix, but the question addressed are not related in
> principle. The Maudlin's stuff (and this is yet clearer in my
> translation of Maudlin's counterfactual moves in term of movie-graph,
> made in "conscience et mécanisme") is that comp + sup-phys entails that
> arbitrary physical processes---including no physical activity at all,
> not even the quantum void---, must produce all form of consciousness.
> It shows than you don't even need to postulate any physical system at
> all. Physics is just irrelevant for consciousness, with comp.
>
> In particular, when you say:
>
> > (3) As a matter of fact, every physical process does give rise to every
> > possible conscious experience, which means that every possible
> > conscious
> > experience is implemented if at least one physical process exists.
>
> You don't even need that one.
>
> And when you say (see below for the quote of "1),2),3)":
>
> > (2) and (3) lead to very similar results. If (3) is the case, we may
> > not know
> > if we are being implemented on a "real" physical substrate or on an
> > endlessly
> > nested series of emulations with an extreme minimalist physical
> > reality at the
> > bottom. The physical reality seems irrelevant, as in (2).
>
>
> I think comp makes (2) and (3) still much closer, if not identical.
>
>
> =======================
> I quote your "1),2),3)" here:
>
> > It is the association of any conscious experience with any physical
> > process
> > which links the Putnam/Searle/Chalmers/Egan/Mallah/Moravec (and me, and
> > probably many others independently) argument with the Maudlin/Marchal
> > argument. There are at least three, not just two, ways to explain the
> > problem:
> >
> > (1) It is absurd that every physical process gives rise to every
> > possible
> > conscious experience, therefore computationalism must be wrong.
> >
> > (2) It is absurd that every physical process gives rise to every
> > possible
> > conscious experience, therefore consciousness does not supervene on
> > physical process at all, but exists in the domain of pure mathematics;
> > this means that every possible conscious experience is necessarily
> > implemented in Platonia.
> >
> > (3) As a matter of fact, every physical process does give rise to every
> > possible conscious experience, which means that every possible
> > conscious
> > experience is implemented if at least one physical process exists.
> >
> > (2) and (3) lead to very similar results. If (3) is the case, we may
> > not know
> > if we are being implemented on a "real" physical substrate or on an
> > endlessly
> > nested series of emulations with an extreme minimalist physical
> > reality at the
> > bottom. The physical reality seems irrelevant, as in (2).
>
>
> This is important because I do not believe, any piece of matter
> implements necessarily all computations. If Loop Gravity is a correct
> marriage of QM and General Relativity (GR), I can assure you that none
> of the Fi(i) are computed when i is bigger than let us say OMEGA +
> [OMEGA] + OMEGA (or any very big but finite number). If string theory
> is correct it is less easy for me to drive a conclusion, but string
> theory put also bound on computability power (as shown by Seth Loyd).
> Contrariwise: the UD does compute all the Fi(i).
> I don't insist too much on this because the Mallah implementation
> problem is really non relevant: comp shows that all physical activities
> emerge from number relations.
>
> Bruno
>
> http://iridia.ulb.ac.be/~marchal/
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Received on Tue Sep 05 2006 - 11:52:12 PDT