Le 25-nov.-05, à 01:10, Stathis Papaioannou a écrit :

Bruno Marchal writes:If on the basis of a coin toss the world splits, and in one branch Iam instantaneously killed while in the other I continue living,there are several possible ways this might be interpreted from the1st person viewpoint:(a) Pr(I live) = Pr(I die) = 0.5I hope everyone sees that this (a) is not defensible once we *assume*comp.Good, we agree here. I don't think everyone on this list would agree.(b) Pr(I live) = 1, Pr(I die) = 0And this one (b) is a consequence of comp.(c) Pr(I live) = 0, Pr(I die) = 1Option (c) may look a bit strange but is the one that I favour: allfirst person experiences are transient, all branches are dead ends,no world is accessible from any other world.I think I figure out why you say that and why you take it probably asa consequence of comp.Let us see.However, the various independent, transient observer moments areordered in such a way in what we experience as ordinary life thatthe illusion of (b) occurs.Yes right. But that "illusion" is all what the first person notion isall about. Your "c" is too strong. What would you say if your compdoctor proposes you an artificial brain and adds that the Pr(I die),for you, is 1. I think you would say "no doctor". Then the doctor(not you!, I know you are doctor!) adds that in all case Pr(I die) =1. Then you will tell him that he has not given any clue about theprobability your first person "illusion" (I hate this word) lasts.The real question we ask to the doctor is what is the probability my"illusion" will lasts *as* it lasts for any other medical operationwhen it is said the operation has been successful.What I have called "Papaioannou's multiverse" are just your transientobserver moments *together* with the order you are indeed adding onthem for giving sense to ordinary experience. That order *is* anaccessibility relation.OK, you've put that quite well. Even if continuity of identity is anillusion, it is an important illusion. An analogy would be going tothe cinema to see a movie: the "reality" might be that we are watchinga series of still images, but the important thing for the audience isthat the illusion of motion is maintained by having a certain minimumframe rate. So yes, this does give rise to an accessibilityrelationship, but it presupposes a theory of personal identity. Evenon this list, there are people who might say (a) above is the caserather than (b) or (c).

Are you sure?

This covers such (theoretical, at present) cases as the apparentcontinuity of identity between two observer moments that just happento seem to be consecutive "frames" in a person's life even thoughthere is no physical or informational connection between them.But you cannot deny that with comp, there *is* some informationalconnection between them. The connection will appear to be exclusivelymathematical and immaterial. And will appear to be the logical rootof another "illusion": a physical world. We know this by UDA (theUniversal Dovetailer Argument), but we need to isolate completely thestructure of the multiverse extractible from comp if we want toderive the precise physics from comp (and then to compare with theempirical physics to evaluate empirically the plausibility of comp(or of its many variants).What I meant by "informational connection" was actual informationtransfer from one frame to the next, by some physical process. This iswhat happens normally by virtue of the fact that consecutive framesare implemented by the same physical brain. It is also what wouldhappen, in a different way, with teleportation. This is sufficientfor the experience of continuity of consciousness, but it is notnecessary: the appropriate frames or observer moments might occurcompletely randomly in different parts of the multiverse, and thefirst person experience would be the same.

`Yes. But then I argue that just for that reason it is not necessary`

`(and actually it is even contradictory) to assume that there is a`

`physical multiverse. Once you grant the existence of some mathematical`

`Platonia, then all the appropriate frames or observer moments (relevant`

`with the comp hyp) occur (partially randomly though) in some`

`mathematical Platonia. Only from the 1-point of view of the observers`

`will it be like a movie-life.`

(Such is not the case for observation of third persons: the frames orobserver moments must be explicitly ordered, or they will be lost inthe noise).

`Indeed and that is exactly what makes comp still possibly false. This`

`points on the real difficulty of comp: to make sense of the sharable`

`third person points of view. Quantum mechanics succeeds here thanks to`

`the non triviality the way the histories sum up (with they destructive`

`interferences). Now, what I try to convey is that if you ask a`

`universal machines about the way to sum up their own histories, the`

`incompleteness phenomena (about which the machine knows a lot) gives a`

`thorough explanation why the sum is not just the boolean sum of`

`classical probabilities but a quite quantum-like form of sum.`

Is this what you mean by "the connection will appear to be exclusivelymathematical and immaterial"?

`I am not sure. The universal dovetailer argument (+ movie graph) should`

`be enough to see that comp makes physics emerging from a mathematical`

`reality (the set of computations: which is a rare mathematical object`

`close for the transcendental Cantor-like diagonalization procedures).`

`The dialog with machines just confirms this, although it does not prove`

`it of course. I don't think we need the hypothesis of a primitive`

`physical reality once we can explain its appearance without it. And`

`any notion of primitive or primary physical reality raises so many`

`unsolvable questions.`

Bruno http://iridia.ulb.ac.be/~marchal/