> On 22 Apr 2018, at 06:39, Bruce Kellett <[email protected]> wrote: > > From: smitra < <mailto:[email protected]>[email protected] > <mailto:[email protected]>> >> >> On 22-04-2018 04:51, Bruce Kellett wrote: >> From: SMITRA <[email protected] <mailto:[email protected]>> >> >> I think the confusion arises from a failure to distinguish between >> 'local interactions' and 'non-local quantum states'. In the entangled >> singlet case we have a non-local state since it involves two >> particles >> that are correlated by angular momentum conservation no matter how >> far >> apart they are, or whether measurements on the separate particles are >> made at time-like of space-like separations. No one has ever denied >> that the interactions involved in the separate measurements on the >> two >> particles are all local, or that decoherence effects that entangle >> the >> particles with environmental degrees of freedom are all local, >> unitary >> interactions. Decoherence leads to the effective diagonalization of >> the density matrix, and the effective separation of copies of the >> experimenters that obtained different results, but this effective >> collapse of the wave-function is brought about by purely local >> interactions. >> >> The usual many-worlds argument for the absence of non-local effects >> points to the fact that all the interactions involved in measurement >> and decoherence are purely local to argue that there is no >> non-locality. But this entirely misses the fact that the original >> singlet state: >> >> |psi> = (|+>|-> - |->|+>)/sqrt(2) >> >> is intrinsically non-local. It refers to correlations due to angular >> momentum conservation that persist over arbitrary separations, and >> these correlations are neither enhanced nor destroyed by any number >> of >> purely local interactions. >> >> So many-worlds or many-minds interpretations of quantum theory do >> not >> obviate the need for non-locality: they cannot, because the basic >> state that is talked about in all interpretations is non-local. The >> point to be made is that in no theory, either a collapse or a >> non-collapse theory, are there any non-local interactions: all >> interactions in measurement and decoherence are local. But that does >> not mean that what one does to one particle of the singlet does not >> affect the other particle -- directly and instantaneously. It is just >> that this effect is not instantiated by a local (or non-local) hidden >> variable. There are no faster-than-light physical transfers of >> information. That would involve a local hidden variable, and there >> are >> none such. >> >> The point is that quantum mechanics is weirder that you think in >> that >> it is intrinsically non-local, even though all physical interactions >> are necessarily local. Thinking of the 6 spatial dimensions of the >> separated singlet particles as forming a single point in >> configuration >> space may help one to visualize this. Alternatively, one can note >> that >> the tensor product Hilbert space of the two spin states is >> independent >> of spatial separation. >> >> Bruce >> >> Quantum mechanics is a lot weirder w.r.t. to its non-locality aspects >> in single world theories. It is there that Alice, after she makes her >> measurement, has to wonder how the implied information about Bob's >> measurement result popped up at his place. This is not an issue in the >> MWI. >> >> Saibal >> >> There is no difference between collapse and no-collapse theories in >> this regard. MWI does not eliminate the non-locality in the >> wave-function for the singlet state. This can easily be seen by >> following the unitary development of my state |psi> above through its >> interactions with the measuring device, observer, and the environment. >> The extra worlds in MWI just come along for the ride -- they do not >> add anything of substance to the argument. All the discussion about >> whether Bell's theorem is invalid for MWI because he assumed collapse, >> or he assumed counterfactual definiteness, or he assumed that >> measurements had only one outcome, etc, is totally irrelevant to the >> issue of non-locality. It is in the original quantum state, so it is >> not eliminated by simply retaining all possible measurement results. >> >> Bruce >> >> In the MWI the non-locality becomes a common cause effect that can be traced >> back to the creation of the entangled spins. As pointed out by Vaidman here: >> >> https://youtu.be/jKGuGptafvo?t=1876 <https://youtu.be/jKGuGptafvo?t=1876> >> >> it's in the ordinary collapse models where there is real problem. >> >> Saibal > Vaidman seems to be trying to demolish Bohm in this video -- nothing > intelligent about any "common cause" effect for Bell-type correlations. It > seems that Vaidman is really playing with idea of retro-causality. And such > things are orthogonal to many worlds. Indeed, the whole thing seems very > confused. The only thing that was clear was that Vaidman adamantly rejects > non-locality -- which is not a very scientific stance.
Action at a distance does not make sense with special relativity. It implies making sense of simultaneity. Bell defended this, and the possibility that special relativity is false, just to avoid the MW. But Aspect showed him wrong. Aspect experience is a strong evidence for the MW (which by the way, is a quasi trivial consequences of Mechanism in cognitive science, so “apparent non-locality without action at a distance” was to be expected, even without quantum mechanics. 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.
