Bruno Marchal wrote: > > On 08 Jul 2008, at 18:38, Brent Meeker wrote: > > > >> Bruno Marchal wrote: >>> If I look to a particle in the state "(UP + DOWN)", the state "I >>> cross (UP + DOWN)" >>> evolves (by SWE) to: >>> >>> "I-seeing-UP cross UP + I-seeing-DOWN cross DOWN", >>> >>> I don't see how to avoid this without abandoning QM. >> If we can't show that a quasi-classical world emerges from QM we will >> abandon it - > > > We have already shown (Everett ... Zurek) how quasi-classical worlds > emerge in the memory of classical machines through QM. > QM justifies the *appearance* of classicality.

I don't think this problem is solved. Dowker and Kent's paper was written primarily as an investigation of the consistent histories interpretation, but it's conclusions also seem to apply to Everett+decoherence; namely that in general there are no quasi-classical continuations of a state. > > >> at least as fundamental. Perhaps the long sought quantum >> theory of gravity will come to the rescue. > > > All approaches now keep intact QM. Everett is the one who realize the > more clearly that only the collapse axioms was incoherent with > relativity. Even Bohr admitted that the collapse could not be physical. > Once you abandon the collapse, QM and (special) relativity fit very > well together. That is why all current approaches in quantum gravity > prefer to keep intact QM (and thus the MW) and correct only a bit GR, > in some (different) ways. > By quantifying gravity, i.e. introducing many spaces-times, you put a > (quantum) topological structure on the multidreams. > > > And why do you want a rescue? You betray you are wishing ONE universe, > and certainly I wish ONE reality, but current physics implies Many > alternate histories, and the current theory of mind (computer science, > universal machine introspection) implies it too. > > Scientists are (or should be) agnostic if there is 0, 1, 2, 3, > aleph_zero, ... universes. But today evidences are in between: 0, > aleph_zero, 2^aleph_0. I don't care how many there are - I'm just concerned with the evidence. I was referring to rescuing Everett+decoherence from the problem Dowker and Kent point to. It seems to be the white rabbit problem within QM. >>> The collapse can >>> be explained >>> *phenomenologically* (first person plural) through MW + decoherence. >>> And if I make a decision based on what state I measure on the >>> particle, the divergence will >>> propagate. >>> >>> And Weinberg has given a convincing argument that once SWE is made >>> slightly non >>> linear, then, not only we keep the Many Worlds/Dreams, but >>> interaction >>> is made >>> possible between them (falsifying then thermodynamics though: that is >>> why I don't >>> take that the delinearisation of the SWE idea very seriously). That's >>> speculation. >> Do you have a reference for Weinberg? I'd like to read his paper. > > > > > > I'm afraid I will not find quickly my copy which I have not read for > many years, but I found a (physicist's, without title) reference: > > > S. Weinberg, Ann. Phys. (N.Y.) 194, 336 (1989) > > > Perhaps more helpful is this: > > http://prola.aps.org/abstract/PRL/v66/i4/p397_1 Thanks. > > (at the time I thought I could easily proof that Plaga + Polchinsky + > Weinberg implies the existence of absolute elasticity, and thus on > some continuous matter/energy/space-time/information, but of course it > appears harder than I thought and I abandoned the project: that would > NOT have contradicted Mechanism, on the contrary). > > > > >> I wonder how it would apply to the idea that there is a smallest >> unit of >> probability amplitude. >> > > > > Except perhaps for some interpretation of Loop Gravity, but I don't > see why they would be a smallest unit of probability amplitude. > From the UDA it is rather clear that this could not exist, unless you > introduce some ad hoc non computable criteria of equivalence. I would think that something like it would follow from the UDA. Aren't all the values integers - reals only occurring as limits. I've only seen one paper that considered the possibility. I postulated a finite, closed universe so that probabilities could be propagated backward. > And from QM? You are thinking about loop gravity? > > > > >> Do you agree that the other forms of multiverse, besides Everett's, >> are >> speculative? > > > > i am not sure I understand. Which other forms you are thinking about? The eternal-inflation universes of Guth for example or the sprouting universes of Carroll. Or Tegmark's all-mathematical-structures. > > Recall that I believe in no more than positive integers, and addition > and multiplication. Which would rule out almost all of Tegmark's mathematical structures. >Then from inside (defined by machine > introspection ...) an ocean of realities develop in many many > directions, and fuse as often, at many many levels. Today the > mechanist hypothesis still a priori implies more universes than those > we "observe" indirectly by the quantum superposition. Yes, I made the point that almost *any* theory that explains the existence of our universe as a natural event following some rules will as well imply the existence of other universes. But I regard all the extant explanations as speculative. Brent > > Today the charge has changed. Those who speculates on *one* physical > universe should give at least one reason or evidence of that unicity > (other than habit or wish). > That idea just doesn't fit the facts, nor two independent theories (in > not so unrelated matter admittedly). > > Bruno > http://iridia.ulb.ac.be/~marchal/ > > > > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Everything List" group. 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