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 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.
Bruce
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:
https://arxiv.org/abs/1906.03440
"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."
Saibal
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