Guys, this is really good stuff. This is answering my question of a couple
of weeks ago. I will quote it in a paper with your permission.
----- Original Message -----
From: Marchal <[EMAIL PROTECTED]>
Sent: Friday, March 02, 2001 1:32 PM
Subject: Re: on formally describable universes and measures

> Jacques Mallah wrote:
> >    Sorry, that doesn't help.  What do you mean by a "real actual" one?
> >What other kind is there, a fake one?  Either it exists, or not.
> OK. In that sense we agree that the DU exist. I am glad to see that you
> are
> a classical platonist. An intuitionist would'nt accept the idea that
> something exist ... or not.
> > Of course, in your macintosh example, the UD was itself implemented by
> >some other mathematical structure - your "local decor".  Does that
> A big part of my reasoning is that it *doesn't matter* indeed. For most
> people this is a difficulty.
> >Actually, I would say that any mathematical structure that has real
> >existance (in the strong sense) should be called "physical".I do not know
> >of any better definition for "physical existance".
> What is that strong sense of existence?  And why do you want to
> classify as physical any mathematical structures.
> If you do that (a little like Tegmark) you are obliged to explain how
> we feel a difference between physicalness and mathematicalness (why is
> there math courses and physics courses) etc.
> Tegmark, like Everett, *do* distinguish the first and third person,
> which helps to make sense of that idea. The physical would be
> some mathematical structures sufficiently rich for having "inside
> point of views" (through SAS point of views for exemple).
> The physical point of view (pov) would correspond to these internal pov.
> >Nowhere did I say that _only_ a "physical" system could implement a
> >computation.  But you did bring to my attention the fact that I should
> >the definition of "implementation" more clear on this point.  In other
> >places, I do point out that one computation can implement another.  (In
> >turn, the second one might implement another, etc.; the first one will
> >therefore implement all of those.)
> >So, your objection is irrelevant.  You do believe a UD implements other
> >computations.
> Sure. Yes. UD implements all computations, and even all implementations
> of all computations.
> >>Actuality is a first person concept.
> >
> >   I have no clue as to what you mean.
> In Newtonian Physics one could imagine some third person time (objective
> time), but since relativity I guess most believe that time is either
> a parameter or do refer to some relative measurement done by an observer.
> "Actuality", "modern", "here", "now", "there", "elsewhere", are words
> with meaning dependent of the locutor. Indexicals, as the philosophers
> call them.
> Most are true or false only from a first person point of view.
> >>3rd person view is everything you can communicate in a scientific manner
> >>without taking into account the subjective view of a person.
> >
> >    If the person has some set of beliefs, they can be described as part
> >the true description of the situation.  (Which you is what I thought you
> >call the "3rd person view".)
> Concerning *believes* the case is arguable. For *knowledge* I don't
> think you will ever succeed in describing them in some provable
> (objectively, 3-person) way.
> This can be proved with very reasonable definition.
> See ref by Benacerraf, or Kaplan and Montague in my thesis.
> (It is linked with that "reconstruction of Lucas" which makes difficult
> for Schmidhuberians to locate an observer in *a* computational history,
> but
> I think that point is obvious once you get the computational
> indeterminacy
> from the duplication thought experience).
> Science is (ideally) a pure 3-person discourse and will ever be. But with
> definition of 1-person you can make science (i.e. 3-person discourses)
> *about* the possible 1-person discourses.
> I give two definitions of 1-person discourses. The first one appears
> in the self duplication thought experiment, and is just "personal
> memory" (what is written  in *your* personal diary). The second one,
> which I use in the formal part of
> my work is the one given by Thaetetus to Socrate. Mathematically it
> gives intuitionnistic logic (topos, constructive math, etc.).
> The use of topos(*) by quantum cosmologist (cf Lee Smolin) is the logical
> move made by those who want the other universal stories away.
> It is cosmo-solipsism.
> Someone who would have only first person insight is a solipsist.
> Someone who would have only third person insight is a zombie.
> If I duplicate myself succesfully in Washington and Moscow, both
> Bruno1 and Bruno2 can communicates the success of the experience from
> a third person point of view, but none can explain you that he feels
> to be the Washingtonian (resp Moscovian) one.
> The difference between the first person and the third person is
> basically the same as the difference between having an headache and
> having a friend having an headhache.
> >From third person truth you need to bet on a theory (even as vague
> as some "habits"). For first person truth you cannot bet on a theory,
> it seems nature has done the bet for you. Humans are probably
> animals which are learning to distinguish them.
> The difference is indeed reflected in language through the distinction
> between I and It/He/She.
> Some people says that that distinction is an illusion, OK, but
> then *I* show that Physics (F= ma, Schr. Eq.) is a by product of the
>  mathematics of that illusion. (it is a true illusion, and that
> is why the word illusion is misleading).
> >Does "merde" have a special meaning, the way
> >"crap" does?
> Some time ago "merde" was considered as very vulgar, but since then
> it has been overthrown by "shit", or worse ... "Merde" seems almost
> polite in comparison.
> I don't know about "crap". It seems to me we don't use that
> word (in Belgium).
> Bruno
> (*) Topos is the mathematical universe of a vast variety of
> intuitionnist/constructivist/solipsist/cosmo-solipsist.
> The original use by Isham is more philosophically rigorous than
> the one by Lee Smolin in his book "three roads to quantum gravity".
> Note that S4Grz gives rise to an arithmetical topos.
> Nevertheless Lee Smolin's book (Weidenfeld and Nicolson,
> London 2000) is very entertaining. And at last begin to ask
> what choose the physical law.
> Toposes or topoi are mathematical first person. I am excitated
> as seeing them appearing in physics. No doubt some will
> believe (wrongly) that they makes the *other* universes
> dispensable.
> A topos is a rich category, giving cool semantics for
> (intuitionistic) math. They have been invented/discovered
> independently by Grothendieck (french)
> in the field of agebraic geometry and Lawvere (American) in
> the field of the foundation of mathematics (in the middle
> of last century (the 20e!)).
> You can find Isham paper in the quant-ph.

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