On 11 June 2017 at 10:14, Bruno Marchal <marc...@ulb.ac.be> wrote: > > On 09 Jun 2017, at 20:21, David Nyman wrote: > > On 9 June 2017 at 12:34, Bruno Marchal <marc...@ulb.ac.be> wrote: > >> >> On 08 Jun 2017, at 02:05, Bruce Kellett wrote: >> >> On 7/06/2017 10:38 pm, Bruno Marchal wrote: >>> >>>> On 07 Jun 2017, at 11:42, Bruce Kellett wrote: >>>> On 7/06/2017 7:09 pm, Bruno Marchal wrote: >>>> >>>>> On 06 Jun 2017, at 01:23, Bruce Kellett wrote: >>>>>> >>>>>> I have been through this before. I looked at Price again this morning >>>>>>> and was frankly appalled at the stupidity of what I saw. >>>>>>> Let me summarize briefly what he did. He has a very cumbersome >>>>>>> notation, but I will attempt to simplify as far as is possible. I will >>>>>>> use >>>>>>> '+' and '-' as spin states, rather than his 'left', 'right'. >>>>>>> >>>>>>> He write the initial wave function as for the case when you and I >>>>>>> agree in advance to have aligned polarizers: >>>>>>> >>>>>>> |psi_1> = }me, electrons,you> = |me>(|+-> - |-+>)|you> >>>>>>> = |me, +,-,you> - |me,-,+,you> >>>>>>> >>>>>>> He says that at this point no measurements have been made, and >>>>>>> neither observer is split. But his fundamental mistake is already >>>>>>> present. >>>>>>> >>>>>>> A little test for you: what is wrong with the above set of equations >>>>>>> from a no-collapse pov? >>>>>>> >>>>>>> skipping some tedium, he then gets >>>>>>> >>>>>>> |psi_3> = |me[+],+,-,you[-]> - |me[-],-,+,you[+]> >>>>>>> >>>>>>> where the notation me[+] etc means I have measured '+', you[-] means >>>>>>> you have measured '-'. >>>>>>> >>>>>>> He then claims that the QM results of perfect anticorrelation in the >>>>>>> case of parallel polarizers has been recovered without any non-local >>>>>>> interaction! >>>>>>> >>>>>>> Spoiler -- in order to write the final line for |psi_1> he has >>>>>>> already assumed collapse, when I measure '+', you are presented *only* >>>>>>> with >>>>>>> '-', so of course you get the right result -- he has built that >>>>>>> non-locality in from the start. >>>>>>> >>>>>> >>>>>> ? >>>>>> >>>>>> From the start shows that it is local. >>>>>> >>>>> >>>>> Your failure to see the problem here is symptomatic of your complete >>>>> failure to understand EPR in the MWI. >>>>> >>>> >>>> I could say the same, but emphatic statements are not helping. My >>>> feeling is that you interpret the singlet state above like if it prepares >>>> Alice and Bob particles in the respective + and - states, but that is not >>>> the case. The singlet state describe a multiverse where Alice and Bob have >>>> all possible states, yet correlated. >>>> >>> >>> The singlet state is rotationally invariant, yes, and can be expanded in >>> any basis of the 2-d complex Hilbert space. That has never been in doubt. >>> >> >> OK. >> >> >> >>> Then in absence of collapse, all interactions, and results are obtained >>>> locally, and does not need to be correlated until they spread at low speed >>>> up their partners. >>>> >>> >>> That does not follow. Although there are an infinity of possible bases >>> for the singlet state, these are potential only, >>> >> >> I don't understand this. Potential? That is no more the MW. >> >> >> >> >> >> and do not exist in any operative sense until the state interacts with >>> something that sets a direction. >>> >> >> That looks more like Bohr than Everett. >> >> >> >> >> You appear to claim that A and B exist in separate worlds corresponding >>> to each of this infinity of bases. >>> >> >> Yes. It is the rotaional invariance of the singlet states "taken >> seriously" when we drop the idea of collapse, or of special dualism between >> observer and the observed. >> >> >> >> >> But that is a misunderstanding. They are in superpositions in every base, >>> sure, but that does not mean that there are 'worlds' corresponding to each >>> possible base until some external interaction occurs. >>> >> >> This is even more fuzzy than the collapse. It looks like consciousness >> not only reduce the wave, but create the physical reality. That is correct >> in Mechanism, but that is another story. >> >> >> >> As you yourself have said, a world is something that is closed to >>> interaction. But superpositions are not closed to interaction, they can >>> interfere -- as in the two slit experiment, and essentially every other >>> application of QM. >>> >> >> Right. >> >> >> >>> So there are no separate worlds corresponding to every possible >>> orientation of the polarizers. Worlds can arise only after interaction and >>> decoherence has progressed so that the overlap between the branches of the >>> superposition is zero (FAPP if you like). It is only then that the branches >>> can no longer interfere (interact) and are closed to interaction, and thus >>> constitute different worlds. >>> >> >> We will have to disagree with this. I use the Y=II rules, like Deutsch. >> In this case the reading of the singlet state gives 2^aleph_zero constantly >> spreading histories figuring Bob and Alice. With mechanism, those >> worlds/histories are more like dreams. They will be epistemological >> personal (and plural in the spreading interaction based spheres). >> >> >> >> >>> The standard procedure in quantum mechanics when one is faced with a >>> superposition that interacts with something external, is to expand the >>> superposition in a base that corresponds to the external context. >>> >> >> OK. In this case, Alice choose to measure her spin. This will only >> self-localized here in one (actually still aleph_0) histories, where she >> will know her states, and the states of any Bob she could soon or later >> interact with, but not of the inaccessible Bobs, who might found non >> correlated result. yet,n him too will be able to met only the Alice(s) >> having the correlated spin. > > > Why? > > > > That is due to the singlet state. [Alice Bob ( up down - down up) ]= > [Alice Bob up down - Alice Bob down up] keeps its rotational symmetry, even > after the interaction took place. The correlation are built in by the > preparation of that state, and is valid whatever the spin direction are, so > you can add prime to up and down, for the other direction, and the > correlation does not depends on the base, and evolve locally. When space > separated, they are independent, but by virtue of the singlet state, if > they do measurement, they will put themselves in "independent" and possible > different superposition, which will 'contagiate' their respective > environment up to *different* partners who will get the right correlation > by the math of the singlet state which will not allow any Alice and Bob to > not confirm the singlet , highly correlated state. The singlet state > describe an infinity of Alice and Bob, having all their spin being > correlated, and they localize themselves in which one when doing > measurement. This can be used to show that they will conclude that Bell's > inequality is violated, despite no influence at a distance exist. There is > only spreading superposition, and all Alice and Bob can only meet their > corresponding partners. >
If this is so easy to describe, why isn't it the 'obviously correct' answer in MWI terms? In Wallace's book, whilst he says that the correlated measurements are 'inseparable', he doesn't go so far as to give an explanation in the clear-cut terms you outline above. I think we need to explore your idea of 'contagiate' a little more. David > > Bruno > > > > > David > >> >> >> >> >> >> >> That is what happens when an unpolarized spin meets a polarizer aligned >>> in a particular direction -- one expands the rotationally symmetric >>> unpolarized state in the basis matching the external context. That is all >>> that is happening with the singlet state above; when Alice comes to measure >>> the symmetric state, it is convenient to expand the singlet state in a >>> basis that corresponds to the orientation of Alice's polarizer. >>> >> >> OK. But that does not make his branch more real. In the MW picture, all >> outcomes are found by Alice in the "parallel universe/dream". >> >> >> >> >> Then the result of the interaction is easily calculated. If one use some >>> other basis, in some other direction, one would end up with a superposition >>> of states after measurement, and that superposition would be exactly the >>> same as the eigenstate obtained when one expanded in the aligned basis. So >>> using a different basis merely complicates the calculation, it doesn't >>> actually change anything. It is like trying to drive from Melbourne to >>> Sydney using a map based on an orthographic projection based on Brisbane. >>> You might manage it, but it would be needlessly difficult. >>> >>> I am sorry that I have had to spend so much time on this diversion into >>> Quantum Mechanics 101, but you seem determined to fail to understand the >>> application of the most fundamental of quantum principles. >>> >>> So, in the measurement of the singlet state >>> >>> |psi> = (|+>|-> - |->|+>), >>> >>> the basis is arbitrary until someone wants to measure this state. If >>> Alice measures the state, we expand in Alice's basis and get the above; >>> Alice has a 50/50 chance of getting '+' or '-'. What is the state after >>> Alice makes her measurement? According to quantum mechanics, the >>> measurement reduces the state to the eigenvalue corresponding to the >>> measurement result. >>> >> >> >> That is not the MW. There is no measurement reducing anything. The >> singlet superposition is just lifted to Alice memory. You really seem to >> work in pre-Everett quantum mechanics. >> >> >> >> >> >> This is entirely local, and is necessary because of the experimental fact >>> that repeated measurements of the same state give the same result. >>> >> >> Yes, that is true for all Alices. >> >> >> >> So if Alice got '+', the state reduces to |+>|->, and if she got '-', the >>> state reduces to |->|+>. >>> >> >> ? >> >> From her perspective, it looks like that, but what actulaly happenes is >> that |psi> has become first (|Alice>|+>|-> - |Alice>|->|+>), which keeps >> the rotational symmtery. >> >> >> >> >> >> This is fine for Alice locally, she is actually measuring only the first >>> part of the superposition |psi>, the part corresponding to her particle. >>> But the second part of the state, the '|->' part in |+>|->, corresponds to >>> the particle that Bob has at his remote location. If everything is local, >>> then Alice's measurement cannot affect Bob's particle, >>> >> >> Indeed. >> >> >> >> so Bob must also be presented with the original state |psi>. >>> >> >> >> Which Bob? >> >> >> >> >> His situation is then exactly like Alice's, we expand the symmetric >>> singlet state in the basis corresponding to Bob's polarizer, and find that >>> he, too, has a 50/50 chance of getting '+', or '-'. It follows immediately >>> that if the two measurements are indeed independent, and they are both >>> measuring the same state unaffected by the other's measurement, both get a >>> 50/50 mix of the two possible results. And, crucially, their results will >>> be totally independent, there will be no correlation. Independent >>> measurements must lead to uncorrelated results, that is what 'independent' >>> means. >>> >>> But we know that, experimentally, Alice's and Bob 's results are >>> correlated, >>> >> >> In their respective parallel realities. >> >> >> >> >> anything between -1 and +1, depending on the relative orientation of >>> their polarizers. So the measurements that Alice and Bob make cannot be >>> independent: Bob's measurement is affected, in some way or another, by the >>> measurement that Alice makes (or vice versa). That is the origin of the >>> claim of non-locality. >>> >> >> Once Alice make a measurement, she only localized herself in he worlds >> where Bob *has* the non independent corresponding state. But all results >> have been obtained (here + and -, times 2^aleph_0). >> >> >> Before Bell, one could imagine that there was some hidden variable that >>> carried an interaction from Alice to Bob. That might have been reasonable >>> if Alice and Bob had a timelike separation, so that Bob's measurement was >>> in Alice's forward light cone. But experiment shows that the correlations >>> are the same even if Alice and Bob make their measurements at space-like >>> separations, so no sub-luminal hidden variable interaction could connect >>> the two measurements. That is non-locality. >>> >> >> That non-locality is not questioned. Only that it shows some action at a >> distance. >> >> >> >>> The question then, is whether many worlds can provide a fully local >>> account of this situation. I claim, with most present day physicists, that >>> MWI does not provide any such local account. >>> >>> After all this, we can go back to Price as above. He writes: >>> >>> |psi_1> = |me, electrons,you> = |me>(|+-> - |-+>)|you> = |me, +,-,you> >>> - |me,-,+,you>. >>> >>> His expansion of 'electrons' into the singlet state is correct, but he >>> then takes this to give: >>> >>> |me>|+->|you> - |me>|-+>|you>. >>> >>> So that if I measure '+', you are presented with the collapsed state >>> |+>|-> (in my basis). Similarly if I measure '-', you receive the >>> corresponding collapsed state. But the |+>|-> in my basis state corresponds >>> to a |+> polarization for my electron and a |-> polarization for your >>> electron -- and you and I are widely separate, possibly by indefinitely >>> large space-like distances! In other words, Price has built the standard >>> quantum mechanical non-local collapse into his account. >>> >> >> I don't see this. There are no collapse having occur at all. >> >> >> >> Not unnaturally, he gets the correct correlation results, but then he has >>> done nothing different from the standard non-local quantum account, so it >>> is no surprise that he gets the same answers. >>> >>> Tipler does exactly the same thing with his account of measurements at >>> arbitrary polarizer angles, differing by theta. And I hope it will not be >>> necessary for me to go through this tedious analysis for that case too -- >>> it is exactly the same mistake, doing the standard QM calculation and >>> claiming that it is totally local. >>> >> >> I see the QM non-locality, but the apparent action at a distance would >> exist only if we suppress the parallel realities in which Bob get the non >> correlated results, despite both of them will be able to interact only with >> their correlated partner. >> >> >> >> >> >>> >>> Another argument is that the linear wave description is described by a >>>> differential equation which imposes locality, and make the non-locality >>>> only apparent in *all* branches (assuming the singlet state to be 100% >>>> pure). >>>> >>> >>> The argument from linearity fails because Schrödinger's equation is >>> linear only in configurations space, and the two-particles singlet state is >>> also defined only in configuration space -- each particle exists in its own >>> 3-subspace of the total configuration space. So while the particles may be >>> widely separated in ordinary physical 3-space, they are in different >>> subspaces of configuration space, and that might be completely local! So it >>> might be the case that linearity implies locality in configuration space, >>> but that does not carry over into ordinary 3-space. >>> >> >> There is no ordinary 3-space, but 2^aleph_0 3-spaces. Quantum mechanics >> without collapse consists in taking the configuration space seriously. >> >> >> >>> As an aside, on an historical note, apparently Schrödinger originally >>> envisaged his 'wave' as a physical wave in space-time, just like an >>> electromagnetic wave or some such, and that his equation governed the local >>> deterministic evolution of this wave in 3-space. When Schrödinger's >>> formalism was applied to two-body systems, such as the hydrogen atom, it >>> was realized that each of the two particles had to exist in separate >>> subspaces of configurations space. Schrödinger was devastated by this >>> finding, and apparently even went so far as to say that he wished he had >>> never invented that 'stupid equation' (or something similar). >>> >> >> No doubt that quantum mechanics is conceptually shocking. The wave is >> physical, but quite unlike sound wave living in a 3-d space. >> >> >> >> >>> I agree it is weird that the "phase space is the real thing", but that >>>> is where the quantum weirdness comes from. Yet, the MWI just abandon the >>>> CFD, I don't see, in the Bell inequality violation any reason to believe >>>> that a influence at a distance should be called for. >>>> >>> >>> As I have said, this simply means that you have not understood it >>> properly. Incidentally, CFD is just a red herring -- nothing in either >>> Bell, CI, or MWI ever depends on the violation of CFD. >>> >> >> It is always supposed by thinking that Alice and Bob have the same >> identity from the beginning to the end of the experience. >> >> >> >> >>> I can go through that in the sort of tedious detail that I have used >>> above if you really must, but I would prefer that you just accept normal >>> physical practice: >>> >> >> The problem is not in the practice, but in looking at the complete MW >> picture. We do not put the violation of Bell's inequality into doubt. Only >> the claim that it shows spooky action at a distance. That is a mono-branch >> account. (Sorry for having use "local" with that meaning in some post, >> which is of course confusing here). >> >> >> >> which is that when faced with a superposition, a detailed calculation on >>> a typical member of the superposition is all that is required. We then sum >>> over the result for that typical component, with weights appropriate for >>> the weights of each component in the superposition, in order to get the >>> final result. So if there are several terms in the superposition, there is >>> no violation of counterfactual definiteness, and one can calculate on just >>> one typical member. Once again, that is all that happens here, and it is >>> just standard quantum mechanics. >>> >> >> That practice is very good ... for applying the theory, and Shor results >> shows that we can exploit the Bell base, and so it is fine, and >> non-locality, or better non separability, is quite real. But to infer from >> this the existence of some action action at a distance is, I think, quite >> incorrect. You need to take into account the fact that when Alice and Bob >> are space-separated, what they will measure does not need to be correlated, >> and they will belong to separate branches of the "universal wave", and will >> never been able to talk with each other and compare their result. They can >> compare their results only in their own branches obtained from some local >> decoherence spreading of they respective result measurement, and conclude >> that they are correlated. No need for a physical "real" action at a >> distance *in* any of the multiple branches of the wave. The uncorrelated >> results which can be obtained makes their corresponding eigenstate >> orthogonal or quasi-orthogonal. >> >> Bruno >> >> >> >> >> >>> 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. >>> >> >> http://iridia.ulb.ac.be/~marchal/ >> >> >> >> >> -- >> 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. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > > > http://iridia.ulb.ac.be/~marchal/ > > > > -- > 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. 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