> On 22 Aug 2018, at 01:54, Bruce Kellett <bhkell...@optusnet.com.au> wrote: > > From: Bruno Marchal <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>> >>> On 21 Aug 2018, at 14:53, Bruce Kellett <bhkell...@optusnet.com.au >>> <mailto:bhkell...@optusnet.com.au>> wrote: >>>> This is discussed since the beginning of QM. Stop talking like if only you >>>> understand Everett. >>> >>> Well, it does not appear as though you do either. You keep adding in >>> infinities of observers that are not part of Everett's formulation of QM. >> >> >> There are two sort of infinity here. One which I hope you agree with, like >> when Alice measure the position of an electron prepared in the state of >> lowest energy level of an electron around a proton. The electron state is a >> superposition of all position possible in the corresponding orbital. After >> measurement she is entangled with that electron, and we have an infinity of >> Alice. OK? (I assume of course some classical QM; that might need some >> correction when GR is used). > > I am OK with this, as I have said before. This is just the infinity that > comes with measuring position or momentum of a particle in a wave packet. > >> The other sort of infinity, the one which I think you disagree with, is >> typical for the superposition of tensor products, like the singlet state ud >> - du. Before measurement Alice has the same probability of finding u, or d >> for any measurement she can do in any direction. Both Alice and Bob are >> maximally ignorant of their possible measurement results. The MW on this, or >> a MW way to interpret this, to keep the rotational symmetry, is that we have >> an infinity of couples Alice+Bob, with each couple being correlated. If >> not, some implicit assumption is made on u and d, like it is a preferred >> base. > > But that is not part of quantum mechanics in Everett's or any other > interpretation. It is an infinite superposition that you have added on for > your own reasons. I have previously offered some suggestions as to how you > could create such a superposition in a conventional way. One obvious > possibility is to have Alice choose her measurement angle according to some > random quantum process, such as radioactive decay.
That is not why I am talking about. I do not add any superposition, I use only the fact that a superposition like ud-du is the same as a superposition u’d’ -d’u, so the relative state implied by the first entails the existence of the relative sate of the second. By choosing to measure u/d Alice select its ‘points of view”, and will get a result determine by all the directions (it will be completely random. Yet, in all those Old, Bob has the correlated particles by common cause. It is almost the definition of the singlet state. > > But the problems with any such suggestion are obvious. Firstly, Alice does > not choose her measurement angle in that way, so there is no > super-superposition created. Secondly, this construction does not restore the > rotational symmetry in any case. You might have an infinite number of Alices, > measuring the singlet at all possible angles, but that multi-multiverse is > not rotationally symmetric either! All it needs is for Alice number 7,234,826 > to poke her tongue out and the rotational symmetry is lost! Of course, you > could add yet more multiverses to cover every possible deviation of Alice > from the stationary state. But the process rapidly becomes ridiculous. > > So this Rube Goldberg construction of additional multiverses of > superpositions does not actually restore stable rotational symmetry. So why > propose such a construction? William of Ockham will rise out of his grave to > haunt you for such pointless extravagance of entities! Alice destroys the rotational symmetry in all its universe. Not of the whole wave, where Alice does not exist as a determinate subsystem. > >> And yes, I do assume locality, if only to illustrate that the MW does not >> force the presence of FTL influence (without transfert of information, which >> actually would require a third person indeterminacy in Nature, which I >> doubt). >> >> It is just a consequence of ud-du = u’d’-d’u’, and the fact that this >> implies maximal ignorance of Alice (and Bob) whatever spin-direction is >> chosen. After the choice of Alice, and her measurement, neither Alice and >> Bob will be able to access a different world. All Alice and Bob will have to >> interpret the state like if it was s simple (two terms) superposition. It is >> like suppressing the global phase of the state. > > And what is the problem with regarding it like this? Even if you add in these > arbitrary multi-superpositions, you end up with an Alice making a single > measurement in some particular direction and communicating with her partner > Bob, who was always in the same world. Bt that are two worlds, at some point four, and I multiply them by 2^aleph_0, for many reasons. > All your additional worlds add only smoke and confusion -- they do not > actually change anything of substance. Alice's measurement on the > non-separable state destroys the original rotational symmetry of that state > -- and nothing that you can do will ever restore that symmetry. I need only taking some distance, or quantum memory erasure and restore local symmetries. You might be right, but I am not convince that QM (without collapse) entails the existence of physical FTL (instantaneous) action. To be honest, I do not care so much on this. I don’t think this is really settled. Bruno > > > >>>>> The measurement that Alice makes destroys the symmetry. That is all there >>>>> is to it. There is not some wider symmetry that is preserved. >>>> >>>> That is Bohr theory. Not Everett. A measurement does not change anything >>>> in the big picture. It collapses wave and destroys symmetries only in the >>>> relative first person mind associated to bodies doing the experience. >>> >>> It is not Bohr's theory, it is quantum mechanics. You appear to believe >>> that symmetry cannot be destroyed, >> >> The symmetry is destroyed from the perspective of the one doing the >> experiment. But it is extended to the couple Alice + the singlet state, >> although “rational symmetry” might be have its usual definition slightly >> enlarged. > > I don't think there is any way in which you can "enlarge" the definition of > rotational symmetry and still talk sense. > >>> even though I have given clear examples where this happens. >> >> It was using some collapse. It seems to me. > > What collapse is involved if I add an asymmetrical weight to a bicycle wheel > to destroy its rotational symmetry? > >>> The symmetry is destroyed totally, not just in the mind of the >>> experimenter. If the symmetry is still preserved in some bigger picture, it >>> is up to you to prove this. But you have not been able to do so. It is just >>> an assertion on your part. And that assertion happens to be false. >> >> You seem to believe that a measurement has to change something in the >> physical reality (besides the brain of the observer). But that does not >> happen in the MW. Measurement is only self-entanglement. It broke the >> symmetry of the singlet state, but enlarge it on the system Aice+singlet >> state. > > As I have pointed out, there is no way in which you could ever make such an > idea work. No matter how much you enlarge the Alice+singlet system, the > rotational symmetry can always be trivially broken. > > Face it Bruno, broken symmetries are universal in physics. > > 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 > <mailto:everything-list+unsubscr...@googlegroups.com>. > To post to this group, send email to everything-list@googlegroups.com > <mailto:everything-list@googlegroups.com>. > Visit this group at https://groups.google.com/group/everything-list > <https://groups.google.com/group/everything-list>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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