On 04-03-2022 00:17, Bruce Kellett wrote:

On Fri, Mar 4, 2022 at 4:05 AM smitra <smi...@zonnet.nl> wrote:On 03-03-2022 01:05, Bruce Kellett wrote:On Thu, Mar 3, 2022 at 10:50 AM John Clark <johnkcl...@gmail.com> wrote:On Wed, Mar 2, 2022 at 5:50 PM Bruce Kellett<bhkellet...@gmail.com>wrote:_> Many worlds is not a local theory._Many worlds can explain all known experimental results without resorting to non-local influences because many worlds is not a realistic theory.In that case, if you believe that MWI is local, give me the local account of Bell-type correlations of spin measurements atspacelikeseparations. I will salute you if you can do this, because no oneelsehas ever managed in the past. Realism is completely beside thepoint.BruceIt's trivial, as the dynamics is described by a Hamiltonian that only contains local interactionsAll local Hamiltoinans contain only local interactions. The point here is that the correlations are not determined by a local Hamiltonian. Consider this: All local interactions are separable (have separable states). The entangled triplet state is not separable. Therefore it is not local.This mans that all non-local effects arise via common cause effects. The creation of the entangled pair of spins happens at some space-time point, so it's the result of local interactions. The later when Alice and Bob each receive one of the two spins, they get correlated with the spins they measure, because they and their measurement gear consist of particles that evolve according to the Schrodinger equation too and that evolution also only involves local interactions. This then causes Bob and Alice to evolve in superpositions that are correlated as a result of the initial entanglement of the spin.But the effect of that initial entanglement is only non-locally available at the point of Alice's and Bob's separate measurements. So your account has not eliminated the non-locality -- you have just disguised it by calling it a "common cause" effect. That common cause is only non-locally available to Alice and Bob. Bruce

`Yes, but this non-locality is a trivial issue in the MWI, analogous to`

`common cause effects in classical physics, while in case of a real`

`collapse the nonlocal effect would be present in the dynamics of Nature,`

`die to collapse itself being a fundamental part of the dynamics.`

`For example, in the MWI picture from Bob's point of view, when he`

`measures his spin, he knows that the spin state of Alice in his sector`

`is the opposite. So, if he knows what Alice's polarizer setting is, he`

`knows the superposition in which Alice and her spin will end up in (of`

`course, not Alice's exact state, only as so far the outcome of the spin`

`measurement is concerned in the formal form of a |up, Alice finds up> +`

`b |down, Alice finds down>).`

`It's the fact that Bob knows that he has a copy who found the opposite`

`spin and in that sector the state of Alice is different that makes this`

`not a dynamical non-local effect. But if collapse is real and the other`

`Bob does not exist, then there is a real fundamental problem with this`

`non-locality. Note that we don't need to get into the Bell-type`

`correlations here, these are only relevant to prove that the random`

`results after a measurement cannot be due local hidden variables. Given`

`that this is an established experimental fact we can just assume this it`

`be true. So, Bob collapsing not just his own spin but also Alice's spin`

`is a problem if the collapse is real. But in the MWI there is no`

`collapse, all the other sectors objectively exist, it's just that his`

`and Alice's sector are correlated with all non-local effects having`

`arisen via local dynamics.`

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