On 31 May 2017 at 04:55, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> On 31/05/2017 12:30 pm, Pierz wrote: > > Thanks for these clarifications Bruce. I find your explanations to be very > lucid and helpful - they also confirm my own understanding. > > > Thank you for the kind comments, I try my best to be clear. > > IIRC, you weren't a particular fan of MWI when I last conversed with you > on this list. > > > That is indeed the case. I have several reasons to be dubious about MWI. > Firstly, it amounts to reifying a complex valued function that resides in > configuration space -- I am not sure that this is a well-defined procedure. > Secondly, MWI doesn't really do what it claims to do, which is to provide a > resolution of the measurement problem in QM. MWI doesn't provide any > explanation of the transition from a pure state to the mixed state that is > required for experiments to give definite results. At the crucial point, > MWI simply says "then a miracle happens!" To be more explicit, > deterministic evolution of the wave function by the Schrödinger equation > gives a full account of decoherence, and the dissemination of the coherence > phases into the environment. This reduces the off-diagonal elements of the > density matrix so that the diagonal elements become *almost* orthogonal, > but unitary evolution can't go the whole way. The only way one can reduce > the pure state to a mixture is to trace over the environmental degrees of > freedom, which is to say that the residual phase information is simply > thrown away. This trace operation is non-unitary, and there is no warrant > for it in the SE itself, so it is, in the final analysis, just an appeal to > magic. > Bruce, is it perhaps finally an appeal to observation per se? IOW what you say is of course objectively the case, but perhaps in some way the residual phase information isn't relevant (i.e. can be 'traced over') in the synthesis of the 'observer-observation' relation. If so, this relation could perhaps resolve the 'eternalist' pure state (which after all continues simply to be 'there' in the MWI conception) subjectively into what would give the 'instrumental' appearance, in effect, of the probability density characteristic of a mixture? Then there wouldn't seem to me to be a necessary idea of 'collapse' involved, except in a purely epistemological sense. The term 'subjective' here is more in the sense of some fundamental compositional principle of observer-hood than a restriction to out-and-out 'waking consciousness'. I'm not sure if this has any necessary connection to Lockwood's idea of a 'consciousness basis'. Of course quite clearly any of this would be highly speculative, but I'm wondering if it could make any sense in principle? I'd value your opinion. Thirdly, the non-observed branches in MWI play no essential role in the > theory, so Occam would say that they are inessential entities that should > be discarded. If one is simply going to discard them, and they play no > observable role, why invoke these other branches in the first place? > > I wonder if you'd care to comment on my original argument on this thread - > which has of course now been swamped by the usual brawls. Does not a single > history + the physical insignificance of the notion of a current moment > mean that there is also only a single possible future? > > > We will only experience a single future, but what that future is, is > indeterminate at the present instant. > > And if the future is predetermined in this way, isn't this a serious issue > for single universe models of QM? How can the outcome of quantum events be > both inevitable and random? > > > I don't see that there is only a single possible future. The block > universe notion only requires indeterminate time ordering for spacelike > separated events. The future along and inside one's future light cone is in > the future for all observers, so need not be determined by some other > observer having already seen what happens. The block universe only > constrains the future only in very limited sense -- it is only for > spacelike separations that simultaneity is ambiguous, timelike separations > are not so constrained. > > Quantum non-locality is another matter, however, and there are growing > indications that quantum entanglement and the associated non-locality might > prove to be of fundamental significance for physics -- such as the > possibility that space-time itself might emerge from quantum entanglements. > Yes, I'm reading Wallace's Emergent Multiverse at the moment on this topic, amongst others. Here's some rank speculation in the MWI vein from the observational perspective: Let's say that entanglement does indeed turn out to be very fundamental in the genesis of what we call 'worlds' in the first place. Mightn't it then be the case that observers - who themselves by assumption supervene on a very narrowly-constrained physics - thereby can't help but find themselves observing the equally tightly-constrained consequences of just such entanglement? IOW, trivially, it's a necessary condition of their own existence. So consequently there could be the appearance of non-locality without there being the requirement for actual simultaneity of action across real physical separations (all the more so if this is conceived as preceding the very emergence of space-time itself). I know this argument has an unavoidable flavour of circularity, but again my question is about principle, not proof. I guess it's also an argument for a species of super-determinism, but with all the counterfactuals still permanently in play, as it were. David > > > Bruce > > > > > > On Wednesday, May 31, 2017 at 12:01:23 PM UTC+10, Bruce wrote: >> >> On 30/05/2017 9:35 pm, Bruno Marchal wrote: >> > On 30 May 2017, at 11:28, Telmo Menezes wrote: >> > >> >> I get your point with decoherence. >> >> Again, I would say that it all depends on theories of mind. What does >> >> mind supervene on? Perhaps it is true that every single coupling with >> >> the environment prevents the current observer state to become >> >> compatible with other branches. But can we be sure? I feel that such >> >> certainties come from a strong belief in emergentism (which I cannot >> >> disprove, but find problematic). >> > >> > It is impossible to recohere the past, FAPP. >> > >> > But only FAPP. To make the blue T-rex interfereing with the red-T-rex, >> > we must erase the trace of particle interaction between the T-rex in >> > its whole light-cone, and this without forgetting the particles >> > "swallowed" by the black-holes, etc. It is just completely impossible, >> > but to derive from that the unicity of the past, is, it seems to me >> > (and you if I understood well) is invalid. >> >> I think the recoherence of paths that have completely decohered is more >> than just FAPP impossible, I think it is impossible in principle. One >> major problem with recoherence in general is that information leaks from >> the paths at the speed of light (as well as less slowly for other >> interactions). Since this vital information goes out along the light >> cone, it can never be recaptured and returned to the original >> interaction. Consequently, indispensable phase information is lost *in >> principle*, so the recoherence is, in general, impossible. Of course, >> with carefully constructed systems, where the loss of information along >> the light cone is prevented, recoherence is possible in special >> circumstances, but not in general. >> >> From this, the uniqueness of the past of any decoherent history is >> assured. So deriving the unicity (if I understand this use of the word) >> is by no means invalid -- it is proved. Even if one encounters one of >> those rare situations in which recoherence is achieved, that still does >> not invalidate the uniqueness of the past history -- recoherence, if it >> occurs, simply means that no new branches are formed at that point, so >> the decoherent history remains unique. >> >> >> >>> FWIW, you >> >>> are expressing my own understanding of the situation: there can be no >> >>> superposition of red and green screens or dinosaurs, or dead and >> >>> live cats, >> >>> because there can be no quantum superposition of macroscopic objects. >> >>> Superpositions of wave functions are only possible for systems >> >>> isolated from >> >>> interaction with their environment, which is why quantum computers >> >>> are so >> >>> fricking hard to make: keeping aggregates of particles isolated from >> >>> interactions with the surrounding environment is exponentially more >> >>> difficult as the system grows in size. >> >> >> >> The main question for me is this: can two branches hold different >> >> observer states, if they differ only by things that are not >> >> observable? >> > >> > I would say no, intuitively. I would even say "no" just for the things >> > not observed, even when observable. >> >> I previously answered Telmo's question in the affirmative, viz., two >> fully decohered branches will hold different observer states, even if >> the differences are not observed or observable. So if some trivial >> physical event happens to your body, such as the decay of a K 40 nucleus >> in your foot, this would not be noticeable, or even particularly >> observable even if you were looking for it. But such an event causes at >> least two branches to form every instant -- one in which the decay has >> occurred, and one in which it has not. And since this is a beta decay, a >> neutrino is lost along the light cone in every case of decay. Perfect >> recombination of the branches is, then, according to the above argument, >> not possible. You might object that this decay in my toe did not alter >> my conscious state -- that is correct, but there are now two copies of >> the Moscow man as in step 3, and these can evolve in different >> directions while each remains unaware of the existence of the other. >> They can never recombine and compare diaries! >> >> > But this has to be tempered by the fact that any interaction will >> > count as an observation, making super-exponentially hard to indeed >> > recover a macroscopic superposition in the past, even the very close >> > past. Of course, that might change the day we succeed in building a >> > fault tolerant (topological perhaps) quantum computer. >> >> That will not help in the general case. Our future quantum computer >> might be able to delay decoherence for some useful finite time, but that >> still only retaines the superposition in the said computer, it does not >> help with recombination of decohered branches in general. >> >> > Unfortunately, the T-rex missed them. yet, if a T-rex made a solid >> > topological quantum qubit, in the state 0+1, we would have a past with >> > 0, and a past with 1, as long as we don't look at it. I read, already >> > a long time ago, some experimental evidence of temporal Bell's >> > inequality going in this direction, and I think we don't even need to >> > test them, as we get them with the usual Bell's inequality violation, >> > if we accept special relativity (and some amount of physical realism >> > (not the full materialism, to be sure). >> >> >> The temporal version of Bell's inequality simply shows that the >> ubiquitous non-locality of quantum entanglement occurs even over time. >> And despite your protestations to the contrary, it is now generally >> accepted that MWI does not remove the essential non-locality associated >> with entangled states. This non-locality is even more evident in the >> more recent delayed choice experiments that use entangled photons to >> manipulate photon polarization states non-locally. >> >> Bruce >> > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to everything-list+unsubscr...@googlegroups.com. > To post to this group, send email to everything-list@googlegroups.com. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. 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