On 3/3/2022 9:05 AM, smitra 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 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.
You write "the get correlated", but breaking statistical independence
requires that the instrument settings be *already correlated* with the
spins before they interact with the instruments and Alice and Bob. That
could be thru some common cause, but it seems unlikely when the
polarization settings are determined by photons from many light years
away on opposite hemispheres of the cosmos. That implies a very long
chain of local interactions to the common cause.
Brent
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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