On 9 June 2017 at 12:34, Bruno Marchal <[email protected]> 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? 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 [email protected]. >> To post to this group, send email to [email protected]. >> 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 [email protected]. > To post to this group, send email to [email protected]. > 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
