On Tuesday, April 17, 2018 at 11:53:05 AM UTC, Bruce wrote: > > From: Bruno Marchal <[email protected] <javascript:>> > > On 16 Apr 2018, at 05:33, Bruce Kellett <[email protected] > <javascript:>> wrote: > > From: Bruno Marchal <[email protected] <javascript:>> > > On 11 Apr 2018, at 14:19, Bruce Kellett <[email protected] > <javascript:>> wrote: > > From: Bruno Marchal <[email protected] <javascript:>> > > If you believe in influence at a distance, you are the one needing to show > the evidence of that extra-ordinary fact. > > > The fact is demonstrated by the experiments that test Bell inequalities on > the singlet state. > > > Not at all. This proves the existence of influence at a distance when we > suppose that a measurement gives an outcome, but in QM without collapse, a > measurement gives all outcomes, with varying relative probabilities. > > > The measurement on one of the spin-half particles in the singlet state has > only two possible outcomes. As is often said in discussions of non-locality > in Everettian QM, 'measurements that are not made do not have outcomes!’ > > > Contextually yes. Because Alice and Bob, in most experience, have a common > protocol, in most thought experience, but we need to take into account at > the start all Alice and Bob to see that there will be non influence at > distance, but only sharable self-localisation issues. > > > That is interesting. What you are saying, quite clearly, is that the > starting point is for Alice and Bob to rule out the possibility of > non-locality. That is not a very open-minded or scientific stance. Surely > the point of the thought experiments is to investigate whether or not the > data can be accounted for in a purely local way. To assume from the start > that there must be a purely local explanation is unscientific because you > have already closed your mind to the possibility of non-locality. > > > You did not. You have even considered a singlet state like if it involves > 4 parallel universes, when it involves infinitely many. See more in the > archive. > > > The singlet state involves only four possible combinations of experimental > results > > > We have discussed this, and I have never agree with this. The singlet > state (in classical non GR QM) describes at all times an infinity of > combinations of experimental result. > > > This is false. Even in Everettian QM there are only two possible outcomes > for each spin measurement: this leads to two distinct worlds for each > particle of the pair. Hence only 4 possible parallel universes. Where do > you get the idea that there are infinitely many parallel universes? This is > not part of Everettian QM, or any other model of QM. > > > From Deutsch and many others, but you can deduce it from Everett long > text. Just take the universal wave seriously. > > > I am taking the wave function very seriously for this simple (but closed, > isolated) system of the singlet state formed from two spin one-half > particles. The wave function is very simple: > > |psi> = (|+>|-> + |->|+>), > > within normalization factors. >
*OK. But starting from the postulates of QM, and assuming the subsystems are entangled, how does one arrive at the conclusion that the states of the composite function can be described as elements of tensor product vector spaces? Alternatively, why are entangled states assumed to be members of tensor product states? AG* > The first ket refers to particle 1 and the second ket to particle 2. Note > that this wave function is intrinsically non-local in that it has no > dependence on the spatial separation of the particles -- space and time are > not relevant for this structure. The temporal evolution of this state is > simply the free particle propagation of the two particles to arbitrary > separations (at least until one or the other interacts with something else). > > Note that the standard expansion requires a set of basis vectors. I have > written these symbolically as a |+> or |-> basis, but there is freedom in > the choice of spatial direction for these basis vectors. But note > particularly that the spin measurement is made in the basis chosen by the > experimenter (by orienting his/her magnet). The outcome of the measurement > is + or -, not one of the possible infinite set of possible basis vector > orientations. The orientation is not measured, it is chose by the > experimenter. So that is one potential source of an infinite set of worlds > eliminated right away. The singlet is a superposition of two states, + and > -: it is not a superposition of possible basis vectors. If you think about > it for a little, the formalism of QM does not allow the state to be written > in any way that could suggest that. > > I don't know what Everett says in his long text, but if it is any > different from the above, then it is not standard quantum mechanics. > Deutsch is a different case. He has a very strange notion about what > constitutes different worlds in QM. Standard QM and Everett's > interpretation are very clear: different worlds arise by the process of > decoherence which diagonalizes the density matrix. The net effect is that > worlds are, by definition, non interacting (contra Deutsch's ideas). > > > But even if you can manufacture an infinity of universes, you still have > not shown how this removes the non-locality inherent in the quantum > formalism. > > > You have not shown non locality. > > > I have demonstrated non-locality in the Everettian context many times. The > simplest demonstration was in the timelike separation of Alice and Bob's > measurements. It is in the archives if you don't recall the details. The > argument then is that any local influence that would explain the timelike > separated measurements must also work for spacelike separated measurements, > and that is not possible. > > In the Everett, the locality is preserved by the fact that you need > interaction/measurement at some point, and the superstition get > “contagious” only at the speed of light, something zurek explained well in > his account of decoherence. > > > This is what you suggested above -- your view is that locality is > maintained by refusing to accept the possibility of non-locality. Sorry, > but that does not wash, scientifically or logically. > > Locality is also trivial if you look at each time to the entire multiverse > phase space structure. I don’t see how you perceive any influences at a > distance. > > > You perceive them by doing the Bell-type experiments. Remember that > quantum mechanics is ultimately defined in Hilbert space, and questions of > spatial/temporal separation do not arise there, so it is all local in > Hilbert space. The problem is that converting from Hilbert space (and/or > configuration space) to normal 3-dimensional space with a distinct time > variable, gives rise to some conceptual difficulties. Unless you can come > to terms with these conceptual difficulties, you will never understand > quantum mechanics. One of these conceptual difficulties is that in normal > space-time, quantum mechanics is intrinsically non-local. > > 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.
