On 03-03-2022 01:05, Bruce Kellett wrote:
On Thu, Mar 3, 2022 at 10:50 AM John Clark <johnkcl...@gmail.com>

On Wed, Mar 2, 2022 at 5:50 PM Bruce Kellett <bhkellet...@gmail.com>

_> 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 at spacelike
separations. I will salute you if you can do this, because no one else
has ever managed in the past. Realism is completely beside the point.


It's trivial, as the dynamics is described by a Hamiltonian that only contains local interactions. 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.

What goes wrong in arguments about this issue is when people switch to a classical picture as soon as Bob and Alice arise who with their macroscopic measurement devices measure the spin components in certain directions. The picture in which a macroscopic effectively classical Bob and Alice collapse wavefunctions is not the correct picture. It is only a FAPP effective description of what really is going on, but it will hide the local nature of QM due to replacing the exact description by an effective description.

Another example of how apparent non-locality arises due to replacing an exact QM description by treating effectively classical quantities as classical instead of quantum mechanical, is the Aharanov-Bohm effect:


"In the Aharonov-Bohm (AB) effect, a superposed charge acquires a detectable phase by enclosing an infinite solenoid, in a region where the solenoid's electric and magnetic fields are zero. Its generation seems therefore explainable only by the local action of gauge-dependent potentials, not of gauge-independent fields. This was recently challenged by Vaidman, who explained the phase by the solenoid's current interacting with the electron's field (at the solenoid). Still, his model has a residual non-locality: it does not explain how the phase, generated at the solenoid, is detectable on the charge. In this paper we solve this non-locality explicitly, by quantising the field. We show that the AB phase is mediated locally by the entanglement between the charge and the photons, like all electromagnetic phases. We also predict a gauge-invariant value for the phase difference at each point along the charge's path. We propose a realistic experiment to measure this phase difference locally, by partial quantum state tomography on the charge, without closing the interference loop."


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 view this discussion on the web visit 

Reply via email to