Le 09-juin-05, à 23:12, Jonathan Colvin a écrit :


With comp, and assuming the copies will never be copied again
and are immortal, then "b".  [the experiment is redescribed below]

Ok, but why? Please explain your reasoning.

It is not simple to explain, although it is a consequence of the Universal Dovetailer Argument. It comes from the fact that the measure of 1-uncertainty bears on all computational histories (computation as seen by a first person supported by that computation), and not on the computational states. A similar facts happens with QM. This is argued by David Deutsch when he insists that world's stories does not duplicate but does differentiate. It is also related to Isham Quantum logical structure bearing on the quantum histories.
But the basic idea is simple perhaps: Suppose I must choose between

a) I am 3-multiplied in ten exemplars. One will get an orange juice and 9 will be tortured.

b) I am 3-multiplied in ten exemplars. One will be tortured, and 9 will get a glass of orange juice instead.

OK. Now, with comp, strictly speaking the 1-uncertainty are ill-defined, indeed. Because the uncertainty bears on the maximal histories. Without precision I would choose "b". But if you tell me in advance that all the 9 guys in "b", who got the orange juice, will merge (after artificial amnesia of the details which differ in their experience), and/or if you tell me also that the one who will be tortured will be 3- multiplied by 1000, after the torture, this change the number of relative histories going through the 1-state "orange-juice" or "tortured" in such a way that it would be better that I choose "a". Obviously other multiplication events in the "future" could also change this, so that to know the real probabilities, in principle you must evaluate the whole histories going through the states. To be sure, the reasoning of Stathis is still 100% correct with comp for what he want illustrate, but such probability calculus should not be considered as a mean to evaluate "real probabilities". When you look at the math, this can be described by conflict between local information and global information. It is all but simple. Today I have only "solve" the "probability 1" case, and it is enough for seeing how quantum proba could be justify by just comp. But even this case leads to open math questions. It is tricky in QM too.

Oops I must go now. Sorry for having been quick,

Bruno


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


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