> On 16 Jul 2018, at 03:57, Bruce Kellett <[email protected]> wrote: > > From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>> On 12 Jul 2018, at 14:09, Bruce Kellett <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> From: Bruno Marchal <[email protected] <mailto:[email protected]> >>>>> On 12 Jul 2018, at 04:04, Bruce Kellett <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> >>>>> There are no up' or down' branches. >>>> >>>> >>>> ? (That contradicts directly what you just said). A up-branch is just a >>>> branch where Alice saw or would see “up”. >>> >>> You were the one who introduce up-prime and down-prime branches. I maintain >>> that there are only two branches on each and every measurement, an >>> up-branch and a down-branch. >> >> In which direction? > > In the direction in which the measurement is made.
OK. But there are many, and if they are not orthogonal, there is no trans-world notion available. The first person indeterminacy selection remains local. > One of your enduring mistakes is to confuse the rotational symmetry of the > singlet state with the single basis corresponding to the direction in which > the measurement will be made. I don’t think so. > Once a direction is chosen, the state can be represented as a superposition > of up and down eigenvectors in that direction. No doubt on this. > Other directions are irrelevant to the measurement. The state is not in a > superposition of eigenvectors of every possible orientation. After the measurement is done, and this makes sense only with orthogonal measurement from Alice and Bob parts, if not, as I say above, the notion of belonging to the same world makes no sense. You tall like if a measurement determine which world they are both in, which is true only for particular case, when they made the measurement of the spin or polarisation in correspond direction. > Quantum mechanics does not have any such superposition. The state is a > superposition of just two eigenvectors, although which eigenvectors depends > on the direction chosen. The singlet state is not dependent of the choice of any spin direction. The singlet state is rotationally invariant. We could use any base. > > >>> ...... >>>>> Each measurement splits a branch, but branches never meet or recombine. >>>> >>>> Because they both measure in the same direction (not sure how they do that >>>> btw), but for Bell’s inequality, some measurement are not “orthogonal”. >>>> Partial fusion is in play, which forbids ti associate each personal >>>> experience with any definite Alice (Bob) in the branching. >>> >>> Perhaps I was not sufficiently clear. I am considering a series of N trials >>> in which both Alice and Bob independently choose random magnet >>> orientations. So if the relative angle is theta, the probabilities for >>> combined results are: >>> >>> Alice gets up: then Bob has probability sin^2(theta/2) for up, and >>> probability cos^2(theta/2) for down. >>> >>> Alice gets down: then Bob has probability cos^2(theta/2) for up, and >>> probability sin^2(theta/2) for down. >>> >>> If theta = 0, then if Alice gets up then Bob down 100%.; Alice down then >>> Bob up 100%. >>> If theta = 120 degrees, then if Alice gets up, then Bob gets up 75% >>> probability, and down 25% probability. >>> And so on for other angles and combined results. It is these probabilities >>> that are crucial for getting the correct correlations when Alice and Bob >>> meet. >>> >>> Now if you can get these correlations without the non-local knowledge of >>> this relative angle, then you have a local explanation. But you will never >>> be able to produce such a set of probabilities locally -- the relative >>> angles are set at random: non-locally at space-like separations. >> >> But the result of the measurement are determined by the singlet state. They >> just cannot known there local angles. > > Of course they know their local angles -- they choose them! The point is that > Alice does not know Bob's chosen angle when she makes her measurement, and > neither does Bob know Alice's angle when he makes his measurement. The fact > that the probabilities depend on the relative angle between these random > non-local choices is the conundrum to be answered. > > >> When they measure in non orthogonal “direction”, the probabilities depends, >> for all Alice-Bod couples, of that state, which is unknown to both of them.I >> am OK that it is non-local, but that does not entail that when Alice makes a >> measurement, she influence Bob’s outcome by a FTL influence. They just get >> aware locally of which sub partition they both belong. > > That is just avoiding the issue. 'Sub-partition' as you use it here has no > meaning. Alice and Bob both know what world they are in -- the world in which > they got up that morning and had their breakfast..... And they are in that > same world when they later meet after a series of trials -- they cannot > change worlds! I don’t see this at all. At each measurement, the worlds, or better the histories are multiplied. The correlation exist, but spread always at the speed of light. Then when they meet it can only be with their corresponding partner. No FTL influence are needed here. > > >>>>> So the Alice that meets a Bob over coffee after the N trials is the Alice >>>>> with one particular branching history. >>>> >>>> Again, this begins to be too much ambiguous, if not non sensical for me. >>> >>> This is the heart of the matter. If you don't understand this, then you >>> don't understand how the correlations are formed. >> >> From entanglement. > > That is meaningless without further explication. The straightforward > explication in quantum physics is that the probabilities for each outcome are > determined by the non-local relative angle between their measurements. No problem with this. > If you want a local account, you have to give it explicitly -- stop just > waving your hands about and appealing to some 'entanglement' magic. On the contrary, the entanglement dispel any magic needed, including magic FTL, which are just not meaningful . The local account is given in all branches of the universal wave. > > > >>>>> The Bob she meets is necessarily in the same world, >>>> >>>> At the moment of the meeting, yes. But that is a far cry to say that it is >>>> the “physical Bob” she started with, in the case of "non orthogonal >>>> measurements”. But OK, for this scenario. >>> >>> We assume randomly non-orthogonal measurements. And neither Alice nor Bob >>> can switch between branches, >> >> ? They don’t know which branches they are in, right at the start. > > Rubbish. There are no branches until they make a measurement. All branches can be better considered as existing at the start, relatively to some fixed base for making the talking possible. a(b + c) is the same wave as ab + ac. In that case, the non-FTL might be easier to see, as it is only consciousness which differentiate along the branch that Alice and Bob can distinguish. > And then each tracks along a particular branching tree as recorded by the > sequence of up/down results recorded in their lab books. There is absolutely > no ambiguity here because neither Alice nor Bob can switch between branches > -- they must always be in the same branch. But when non orthogonal measurement are done, this makes no sense. > >> That is equivalent to belonging to many threads at once. > > This is your 'comp' nonsense. It has nothing to do with quantum mechanics, It is the only explanation of physics that I know which is consistent with the existence of consciousness. Computationalism explain why and how the physical appearance came from, and QM (without collapse) confirms it, with intuitively and formally. > especially not the quantum mechanics of Everett. Branches arise only from > existing superpositions, and there are no infinite superpositions in this > problem. There are much as the possible spin direction Alice and Bob can choose for their measurement. As Everett suggests, that explain locally the EPR phenomenon. > > >> Only later will they get more precision on this. The singlet state explains >> why they will observe the correlations when coming back together, without >> having to have any FTL. > > Once more the appeal to magic. You have to spell out how this happens. I did. I referred also to Pirce FAQ for a good approximation. You are the one invoking the FTL, so I think you are the one who should explain where that comes from, and how to test it experimentally. Aspect experience test non-locality or inseparability, not FTL. > >> Once a superposition exist, it never disappear, and the correlations just >> reflect the type of interaction they did have to prepare the singlet state. >> >>> so the Bob that Alice meets has a set of measurement made all in this same >>> world -- the world in which Alice has made her measurements. >> >> But there is an infinity of such world, where Alice find any possible >> results. Same for Bob. The results are correlated, because they are in the >> right corresponding relations, in all of them. > > There are not an infinity of worlds, there are only 2^N of them. Of course > the correlations come out right for every Alice/Bob pair when they meet. But > you have not explained this locally. That is exactly what the wave explains, when you dismiss all collapse. The wave evolves purely locally in the phase space, which is the real “mutiversal” reality (up to some gauge nuances). > >> My feeling is that you introduce some collapse somewhere. > > I don't have to introduce a collapse: I just choose one branch from the > superposition of 2^N such branches. Since the branch I choose is typical, the > same result obtains for all 2^N such branches. Because each branch is just a > single world, it looks exactly the same as the collapse model of Copenhagen > or some such interpretation. I know you find collapse an anathema, but > collapse is just the same as picking one typical branch from the many-worlds > superposition. In that sense, many-worlds and collapse models are identical. Not at all. In the collapse model, you need FTL to explain the non-locality. But you need FTL in the many-worlds. You need only to take account the first person ignorance of which branches Bob and Alice are in. > > >>> In fact, the multi-branching tree forms a giant superposition, and we have >>> just singled out one component of this superposition. There is nothing at >>> all mysterious in this -- it is what physicists do all the time when they >>> perform calculations in momentum space -- on just one component of the >>> superposition that makes up a wave packet. >> >> That makes sense. > > That is what I have been saying all along, and this is what removes your > worry about 'collapse models' -- they are just a branch from the many-worlds > superposition. I don’t see how you would do that when Alice and Bob makes non orthogonal measurements. > > > >>>>> and he has a similar particular branching history corresponding to just >>>>> one world. There are 2^N such meetings, each with unique branching >>>>> histories. The wonder of the singlet state is that for all these >>>>> Alice/Bob meetings, comparison of the data recorded in their lab books >>>>> always gives correlations that agree with quantum theory and violate the >>>>> Bell inequalities. >>>> >>>> To get them, they need non orthogonal measurement, with different >>>> probabilities (cos^2(some angle)), and your identity relations does no >>>> more work. >>> >>> We have assumed non-orthogonal measurements, ones with the relative angles >>> set randomly at spacelike separation, ie., non-locally. >> >> No problem with this. Still not see why we would need single branch physical >> FTL when we look at the “giant superposition”. > > The "giant superposition", in so far as it exists, has been spirited away by > just looking at a single branch. There is nothing the "giant superposition" > can add to the conclusions obtained from just one branch. ? It changes the result of further possible measurement, notably involving Alice and Bob possible amnesia, in theory. Collapse has to be non local to make sense, as Eistein made already clear in 1927. It is just worst with the singlet state, but here too, avoiding a collapse avoid the need of FTL. > > >> I don’t see at all why and how any FTL would be needed once we agree that >> both the evolution and the tensor product are linear. > > Stop worrying about FTL. There is no physical FTL mechanism Then; like last time, se agree on everything! > . It is just that non-separability of the singlet state means that non-local > measurements will be correlated. There is no deeper explanation than this. In > particular, there is no local explanation. I agree. There is non local explanation is obvious. The key point I defend is only that there is no physical FTL. That was the point where John Calrk disagreed with. > >> I see only local interaction, shared by people belonging to the (infinitely >> many) corresponding states described by the singlet state. > > Sure, the interactions are local, but at non-local positions. Obviously. > Get over the nonsense about infinitely many corresponding states -- that is > your private fantasy and nothing to do with quantum mechanics. It is just the universal wave of Everett. If you agree that there is no FTL, I don’t see any disagreement between us. It is the second if not third time we arrive at this conclusion. It is very weird. 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] > <mailto:[email protected]>. > To post to this group, send email to [email protected] > <mailto:[email protected]>. > 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. 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.
