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