On Thu, Jun 21, 2018 at 12:56 AM, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> From: Jason Resch < <jasonre...@gmail.com>jasonre...@gmail.com> > > > On Tue, Jun 19, 2018 at 12:03 AM, Bruce Kellett < > <bhkell...@optusnet.com.au>bhkell...@optusnet.com.au> wrote: > >> >> I find Baylock's exposition of counterfactual indefiniteness as applied >> in MWI quite opaque. He makes the argument needlessly complicated by >> considering a sequence of experiments with non-aligned filters. Then >> analyses these by comparing to an arbitrary 0º and 90º pair of >> orientations. When he does his general analysis he gets four possible >> worlds as he should, but he does not calculate the probabilities for these >> individually. Rather, he relates the results back to the 0º and 90º >> orientations. And then says that because no measurements were actually made >> at these angles the lack of counterfactual definiteness rules out the >> worlds in which the results do not agree with the quantum predictions. This >> is quite confused. There is no need to consider sequences of measurements >> at different angles, one need consider only one set of such measurments and >> calculate the resulting probabilities for each of the four possible sets of >> results. By doing something quite peculiar, Baylock does nothing more than >> confuse himself into error. >> > > What specifically, is the error? > > > Opacity. There is no need for reference to violations of counterfactual > definiteness, because no comparison with measurements that were possible, > but not made, is ever necessary. The account that I have given only ever > refers to measurements that are actually made. > > > We should concentrate on the simple case that I have presented, where the >> polarizers are aligned by construction, and no reference is made to >> measurements that are not made, but are assumed to have definite outcomes >> (no violation of counterfactual defininteness need be assumed). You have to >> be able to give a local account of why certain combinations of results are >> not observed. You have been unable to do this. >> >> > You agreed both photons are entangled to each other. > > When you measure either of the photons, you too become entangled not only > with that photon, but also with its pair. > > > Entanglement with the partner photon is the non-local effect. The pair is > at a spacelike separation. > But entanglement can spread locally? E.g. from the measurement device, to your eyes, to your brain, to the notebook, etc. All I am saying is that in the EPR case, the "measurement" (entanglement) already occurred, at the time of the photon pair's creation. The result (though not a single definite value) of this "measurement" spread at sublight speeds, to two different locations, where the entanglements spread from there. > > > If someone measures it's partner photon, now you, the left photon, the > right photon, and that other person are now all entangled with each other. > > > There are only two photons, but each has two possible polarizations. When > you measure the polarization, you split into two branches, one for each > possible result. The partner photon reaches the other person on each of > your branches, but if everything is purely local, the photon that is > remotely measured cannot know which result you obtained (it cannot know > which of your branches it is actually on), so it has indeterminate > polarization, and when measured, there is necessarily equal probability for > either result. > I think this is the heart of our disagreement. You are seeing the entangled photons are still distinct objects without a correlation. There are two events where some human experimenter gets entangled with a photon (you could saw under MWI that two splits occur). Now I think you ask why does the second measurement know to "split the right way", but it doesn't, and doesn't need to. Both experimenters contagiously contract the superposition of the photon they measure (entangle themselves with). > > This means that the photon that is on the branch in which your photon > passed the polarizer can either pass the remote polarizer, or be absorbed, > with 50% probability for each. Similarly for the photon that is on the > branch in which your photon was absorbed. The outcome by considering both > branches is four possible worlds, one for each combination of 'pass' and > 'absorb' results. Two of these worlds violate angular momentum > conservation. How do you rule out these worlds with only local interactions? > > The photon pair was created at one point in space time, it traveled only at light speed to two locations, where its superpositional state became entangled with the local environment at its point(s) of measurement. To say there are 4 possible worlds here, I think is to assume measuring the same photon twice using the same polarization angle, can produce inconsistent results. > (entanglement is nothing mysterious, it is equivalent to measurement). > > > Yes, but entanglement, being a local effect, can only spread at, or less > than, the velocity of light. You cannot be entangled with your remote > partner when he does his measurement, because you are space-like separated. > By measuring an element of the entangled pair the partner is entering is entering the same entanglement (or you could say performing the same measurement). > > > When nothing collapses, all you get are local effects, of information (in > the form of particles or fields) moving through space time at light or > sublight speeds. > > > That is the conclusion that you have not been able to establish. The > Bell-like correlations actually have nothing to do with collapse or > non-collapse. The entanglement is intrinsically non-local in either case. > > You never observe the person who got the inconsistent measurement, nor > ever hear their radio signal because you are entangled with the person who > got the result consistent with your measurement. > > > But that entanglement is the non-local effect. > > Look at it this way. The two measurements are made at space-like > separation. If everything is local, the measurements must be independent. > There is where I disagree. The actions are independent, but the results are not. > If the measurements are independent they cannot be correlated -- that is > one possible operational definition of independence. > But when measuring an entangled photon pair, they must be correlated. > Since the measurement results are known to be correlated, they cannot be > independent. Since there can be no sub-luminal interaction between the two > measurements, this correlation can only be a non-local effect. In the case > that I have been discussing, quantum mechanics predicts 100% correlation. > There is no way this can be achieved locally because the singlet you are > measuring is rotationally symmetric and has no intrinsic polarization state > that can be carried subluminally between the experimenters. > In other words, the structure of the singlet state rules out a common cause > explanation for the 100% correlation. Bell's theorem then rules out any > *local* hidden variable explanation. > > Look, the singlet state is: > > |psi> = (|+>|-> + |->|+>). > > When Alice makes her measurement she effectively splits this state into > the |+>|-> state on one branch, and the |->|+> state on the other branch. > I would not say she splits the state, I would say she splits herself, by now becoming part of the state. The super position never goes away so you get two Alices: (Alice * |+>|->) + (Alice |->|+>) The "(Alice * |+>|->)" knows that Bob she will hear from who performs the same measurement of the photon of the entangled pair will be the Bob that sees the - photon, and "(Alice |->|+>)" knows the that the Bob she will hear from who performs the same measurement of the photon of the entangled pair will be the Bob who sees the + photon. > But if everything is purely local, this split does not happen for Bob > before he makes his measurement. > True Bob has not yet entangled himself. But you speak of splits as if they are instantaneous things that create two whole universes instantly. This is not what MWI predicts. > So he, too, measures the original entangled |psi> state, and he also must > have 50% probability of either result. However, quantum mechanics says that > when Alice measures |+>, Bob necessarily measures only the |-> component of > his photon; and when Alice measures |->, Bob necessarily measures only the > |+> component of his photon. > Correct. > This is how the correlation comes about. But this is non-local -- the > non-separable initial state is separated non-locally by the measurements. > But they're measuring (entangling themselves with) the same superpositional state: the entangled (mutually already measured) photon pair. > > > If I send a photon through a filter orientated at 0 degrees, and it > passes through, and goes all the way to Pluto where you measure the filter > at 0 degrees and it also passes, you would not say this violates locality, > would you? > > > No, because its passage to Pluto is at the speed of light. > Same as with the traversal of the photons in the photon pair, is it not? > > > It is the same picture. > > > But it is not the same picture. In the case you mention, you send a > polarized photon to Pluto at the speed of light. In the case of the > entangled singlet state there are two separated photons that are measured > simultaneously (in one frame at least), so no one is sending a photon of > known polarization anywhere. > In the case of EPR, it has a single state, just a superposed state, and one that has not yet entangled itself with any observer yet. Whether I on earth have become entangled with the measurement of the photon or not, doesn't really change anything fundamentally. > > > You might as rightly ask why are future measurements correlated > (entangled) with past measurements. I don't see anything in the theory that > suggests we should expect such inconsistencies in any two successive > measurements (be they of an entangled photon pair, or two measurements of > the same photon). > > > Because in one case information is transmitted at the speed of light and > in the other case the influence is non-local. The entangled state is > non-separable, whereas two measurements on the same photon are separable. > How are two measurements of the same photon separable? > > > Can you elaborate on why you think the Schrodinger equation implies such > inconsistencies ought to arise? > > > It is not really something in the Schrödinger equation. It is in the > nature of the initial state. The Schrödinger equation describes the time > development of the wave function and it operates equally on the single > photon state and on the entangled two-photon state. In the latter case, the > time development (propagation) of the two photons is independent. Besides, > the Schrödinger equation describes multiparticle states in configuration > space, not ordinary 3-space. > > There is no inconsistency since the two cases are quite different -- why > should you expect a single photon to behave in exactly the same way as an > entangled pair? > > Feynman says we can view the pair as the same particle traveling backwards and forwards through time (perhaps not so easily with the photon which does not go through time, but certainly we can with an electron-positron pair as in the original EPR). In this view, the entangled particle can be viewed as the same particle. Jason -- 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. 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