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On Apr 16, 11:16 am, "Quentin Anciaux" <[EMAIL PROTECTED]> wrote: > HI, > > 2008/4/16, nichomachus <[EMAIL PROTECTED]>: > > > > > > > > > On Apr 16, 4:54 am, Bruno Marchal <[EMAIL PROTECTED]> wrote: > > > Le 16-avr.-08, à 03:24, Russell Standish a écrit : > > > > On Wed, Apr 16, 2008 at 02:22:23AM +0200, Saibal Mitra wrote: > > > > >>> First off, how is it that the MWI does not imply > > > >>> quantum immortality? > > > > >> MWI is just quantum mechanics without the wavefunction collapse > > > >> postulate. > > > >> This then implies that after a measurement your wavefuntion will be > > > >> in a > > > >> superposition of the states corresponding to definite outcomes. But we > > > >> cannot just consider suicide experiments and then say that just > > > >> because > > > >> branches of the wavefuntion exist in which I survive, I'll find > > > >> myself there > > > >> with 100% probability. The fact that probabilities are conserved > > > >> follows > > > >> from unitary time evolution. If a state evolves into a linear > > > >> combination of > > > >> states in which I'm dead and alive then the probabilities of all these > > > >> states add up to 1. The probability of finding myself to be alive at > > > >> all > > > >> after the experiment is then less than the probability of me finding > > > >> myself > > > >> about to perform the suicide experiment. > > > > >> The probability of me finding myself to be alive after n suicide > > > >> experiments > > > >> decays exponentially with n. Therefore I should not expect to find > > > >> myself > > > >> having survived many suicide experiments. Note that contrary to what > > > >> you > > > >> often read in the popular accounts of the multiverse, the multiverse > > > >> does > > > >> not split when we make observations. The most natural state for the > > > >> entire > > > >> multiverse is just an eigenstate of the Hamiltonian. The energy can > > > >> be taken > > > >> to be zero, therefore the wavefunction of the multiverse satisfies the > > > >> equation: > > > > > One should also note that this is the ASSA position. The ASSA was > > > > introduced by Jacques Mallah in his argument against quantum > > > > immortality, and a number of participants in this list adhere to the > > > > ASSA position. Its counterpart if the RSSA, which does imply quantum > > > > immortality (provided that the no cul-de-sac conjecture holds), and > > > > other list participants adhere to the RSSA. To date, no argument has > > > > convincingly demonstrated which of the ASSA or RSSA should be > > > > preferred, so it has become somewhat a matter of taste. There is some > > > > discussion of this in my book "Theory of Nothing". > > > > Actually, I am not sure the ASSA makes sense once we take into account > > > the distinction between first and third person point of view. Comp > > > immortality is an almost trivial consequence that personal death cannot > > > be a first person experience at all. Quantum immortality is most > > > plausibly equivalent with comp immortality if the "quantum level" > > > describes our correct comp substitution level. But this does not mean > > > that we can know what shape the comp immortality can have, given that > > > comp forbids us to know which machine we are or which computations bear > > > us. > > > Why is this the case? Whether Comp is true or not, it would seem that > > the direction of physical research and investigation is in the > > direction of discovering the presumed foundational TOE that accounts > > for everything we observe. Say, for example, that it were possible to > > create in a computer simulation an artificial universe that would > > evolve intelligent life forms by virtue of the "physics" of the > > artificial universe alone. Why, in principle, is it not possible for > > those intelligent beings to discover the fundamental rules that > > underlie their existence? They will not be able to discover any > > details of the architecture of the particular turing machine that is > > simulating their universe (even whether or not they are in fact being > > computed), but I don't see any a priori reason why they would not be > > able to discover their own basic physical laws. > > Because from the 1st person pov you cannot tell which computation > (there are an infinities) support you hence the RSSA because the > probability of your next states are relative to the current state you > are. With the no cul de sac (means there exists no universe state > which does not have a next state) comp predict comp immortality... > Hi, Quentin, I am not sure what exactly is meant by cul-de-sac since it seems that, unless we are speaking about observer-moments, there can be no cul-de- sac. (A series of observer moments would seem to me to end with the death of the observer, or else the moment before death, but I am new and so am not familiar with the history of the debates here. I am not sure if that is agreed upon by those reading this list.) How can any state of the universe fail to have a successor? The MWI states that there must be many successors (branches), or, equivalently, merely one -- a continuously evolving universal wave equation. Further, I have heard it claimed that it could be that there are a plurality of possible histories that could have led to the present moment. In such a case it would be nonsense to claim that only one of these grandfather states could lay claim to being the true history, since more than one had degenerated into a single timeline of experiences. That being said, if I consider the claim that some branches of the multiverse of the MWI do not experience the same change in entropy that characterizes the norm of existence -- call them the "fluke" branches -- then there would be no normal arrow of time in these deviant offshoots of history. It is repeated frequently that the laws of physics, both classical and quantum mechanical, are reversible, and that it is only the steady increase of entropy that gives rise to the a unitary perceivable direction or arrow to time. These fluke branches might be considered to be cul de sacs, since entropy would operate entirely differently in these. Does time flow backward in fluke branches? Does it sit still? Consider the implications of the "heat death" scenario, one that had been believed to be a possible fate of the universe. In this scenario, entropy has effectively reached a maximum value, and there is no further energy exchange possible. there would also be no meaning to time in a universe in which nothing could happen. Perhaps in a fluke branch, where entropy falls continuously, or else fluctuates, or stays static, there would no normal perception of the arrow of time. (Of course, not all cosmologists believe that heat death is a possible fate, even in an expanding universe.) > > Max Tegmark has indicated that it may be possible to get some idea of > > which mathematical structure bears our own existence by approaching > > from the opposite direction. Though we may never know which one > > contains ourselves, it may be possible to derive a probability > > distribution describing the likelihood of our location in the > > ensemble. > > That means the universe is not one mathematical structure nor the > multiverse is, but the infinite set of functionnaly equivalent > computation... well from a certain point of view these universes > aren't differentiated... So it is difficult to say that at any moment > we are in such or such computation, we're in all of them (that support > us). Sure, but it makes sense to think about and refer to the simplest, or least complex universe that would produce the universe we find ourselves in. There surely is an infinite equivalence class of structures that are isomorphic, if you will, with our universe. whether the universe is conceived of as a static mathematical entity or perhaps a recursive algorithm, it must have one lowest-complexity formulation that is capable of producing this universe. Although, as pointed out by Tegmark, this lowest complexity structure will likely contain a great deal more than only this universe. This is not to imply that, if the universe is able to be generated from an algorithm, that the stepwise direction of computation bears any necessary relationship to the direction in which we perceive time (up-entropy). However, given what we know about computing physics, one might be excused for assuming naively that, if the quantum level is the most fundamental, or "comp substitution level," the direction of computation might be parallel or anti-parallel with the up-entropy direction, or else these two may be equivalent. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Everything List" group. 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