On Thu, Jun 21, 2018 at 11:48 PM, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> From: Jason Resch < <jasonre...@gmail.com>jasonre...@gmail.com> > > > On Thu, Jun 21, 2018 at 12:56 AM, Bruce Kellett < > <bhkell...@optusnet.com.au>bhkell...@optusnet.com.au> wrote: > >> 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. > > > The entangled photons are a non-separable unity. But if everything is > local, the measurements by Alice and Bob, being space-like separated, must > be equivalent. If Alice splits into two branches, so must Bob. The > correlation arises because the entangled pair is not a local object -- it > has no purely local description. > Something that spreads at <= speed of light, and effects and interacts with only the local particles/fields is not a non-local phenomenon. Here the photon pair (under many worlds) matches both of these qualifiers perfectly. > > > 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). > > > What on earth does that mean? "contagiously contract the superposition". > It can only mean that the superposition is non-local, and that you are > actually making use of this non-locality without being aware of it. > > The superposition starts with the creation of the photon pair, and spreads to everything that measures/interacts with it, and anything that measures/interacts with the thing that measured it, ad infinitum. > > 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. > > > You are confusing measurements on the entangled pair with repeated > measurement of the same single photon. The entangled state is a unity, but > it is not the same as a single photon. > > > They are analogous, and by rotating the picture of space-time when looking at the electron-positron pair in the original EPR thought experiment, you can view the electron-positron pair as the same particle. In the conventional view we see it as a pi meson decaying into e- and e+, with opposite spins. But rotate things about 90-degrees and you see it as an electron interacting with a Pi meson and changing directions. > 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. > > > Then there must be a non-local effect! If the measurements are made > independently at a space-like separation, there can be no correlation > without either a common cause or non-locality. Common cause is ruled out by > the statistics of repeated measurements of such entangled pairs at > different angles. > Common cause isn't ruled out by Bell for measurements that have more than one outcome. > > > > 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. > > > Exactly. So how did this correlation arise? > >From the time of the pair's creation, each element of the the pair has already measured the other. Each element of the pair (while in this superposition) proceeds at <= light speed to a location where it will be measured. Since each element of the pair has already measured the other, measuring either element is equivalent to measuring both (or you might say the same particle, under Feynman's view of antiparticles). > > > 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. > > > How does she know this? And why can't the Alice who sees the |+> not hear > from the Bob who sees the |+>. > |+> Alice is no longer in the same branch as the one containing |+> Bob. They're in the same superposition though. > Both must exist if everything is purely local, you know. > > > Both exist, but the |+> Alice is in the branch where the |-> photon belongs to "her" Bob. > > 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. > > > We are doing measurements with people and macro apparatus that is not > isolated from the environment. So the decoherence following the measurement > splits the world -- locally, of course, but that is all that is required. > Bob is at a space-like separation, so the split occasioned by Alice's > measurement has not encompassed him at the time he makes his measurement. > Is that so hard to grasp? > I agree with this. > > > > 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. > > > What you say here makes no sense. Alice cannot entangle herself with Bob's > photon when she makes her measurement -- it is at a spacelike separation. > Or rather, any entanglement that does occur must be non-local. The > non-separability of the state means the correlations are non-local in > origin. > I am not sure what is meant by "non-separability of the state". > > > > > > > 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? > > > If you think these cases are equivalent, then I am sorry, but there is > nothing more I can say that will ever convince you of your error. > > You deleted my quote from Feynman. Did you disagree with what he says? > One obvious problem with your attempt to equate the measurements on the > entangled pair with repeated measurements of a single photon is that in > neither case do you make any use of many-worlds to explain the EPR-type > correlations.There is no violation of counterfactual definiteness, no use > is made of measurements that could have been performed, but were not. > The EPR-type correlations were explained in the paper I provided, but you said this was "being opaque" and adding confusion. It was your suggestion to keep things simple with an identical orientation for the polarization filter. > So what, exactly, is MWI giving you in your purported explanation of EPR > that is not already available in a collapse model? > Determinism, locality, time-symmetry, reversibility, QM obeyed at all times, no classical-QM cut off point, the absence of FTL effects or influences, and a simpler theory of QM. 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