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. James ----- Original Message ----- From: Marchal <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, March 02, 2001 1:32 PM Subject: Re: on formally describable universes and measures

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> > 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 matter? > > 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 make > >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 of > >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. > > > > http://iridia.ulb.ac.be/~marchal > > > >