On 12/23/2021 2:55 AM, smitra wrote:
On 22-12-2021 22:54, Bruce Kellett wrote:
On Wed, Dec 22, 2021 at 10:12 PM smitra <[email protected]> wrote:
On 21-12-2021 22:48, Bruce Kellett wrote:
In general, that is not true. When both Alice and Bob set their
polarizers randomly while the particles are in flight, the fact
that
Alice might get |up> tells her nothing about what Bob will get at
some
randomly different polarizer orientation. You seem to be stuck
with
thinking in terms of parallel polarizer orientations.
It's not true only when the polarizers are orthogonal. Whenever the
polarizers are not orthogonal, Alice will gain some amount of
information about what Bob will find given the result of her
measurement. For Bob, the probability of finding up or down are
always
1/2, but after Alice makes her measurement, the conditional
probability
of what Bob will find, given her measurement result will not be
equal to
1/2 for both outcomes if her polarizer was not orthogonal to that of
Bob, so Alice will have gained information about Bob's measurement
result.
The conditional probability you refer to is defined only non-locally.
There are no nontrivial nonlocal effects in the MWI. Once you specify
how Alice and Bob decide to choose their polarizers, you can analyze
the flow of information. If you do that within the MWI framework there
won't by any nonlocal effects apart from common cause effects where
information created at one spacetime point ended up travelling in two
directions via local processes and ended up creating correlations in
spacelike separated systems.
In the MWI
there is no such mysterious gain of information due to the
correlation
being caused by common cause when the entangled pair is created
Rubbish. If there were a common cause, then that would have to
depend
on the final polarizer orientations. And those are not known at
the
time of creation of the entangled pair. You are, then, back with
some
non-local influence (or retro-causation).
The setting of the polarizers will be the result of some physical
process. Whatever you specify for that process should be included in
the
analysis of the problem. But when you do so, it's inevitable that in
an
MWI analysis, there is not going to be any nonlocal effect other
than
trivial common cause effects.
I see. So in desperation you resort to the superdeterminism escape.
MWI is not necessary for the understanding of the correlations of
entangled particles, as my simple example shows. In an actual
experiment, the analysis is identical in many-worlds and collapse
models. The additional worlds in MWI add nothing to the explanation.
They are, therefore, otiose, and MWI can be discarded.
As Jesse Mazer pints out this has nothing to do with superdeterminism.
You can e.g. let Bon And Alice do additional spin measurements on
other (non-entangled) electrons and use the random results of those to
determine the orientation of their polarizers. Thing is that you need
to choose some physical process for this. There is then no appeal to
the setting of the polarizer having been pre-determined in a way to
explain the correlations, so this is not an appeal to superdeterminism.
Collapse models invoke new, as of yet unobserved physics, at scales
where our present theories of physics are very solid. While such
collapse theories could be correct, they are not motivated by an
attempt to solve a problem, like e.g. tensions with experimental
results. The MWI, in contrast, is motivated with problems of standard
QM, namely the unphysical collapse of the wavefunction.
Arguing for collapse models today is like what would have happened if
not Einstein but Maxwell had invited the theory of special relativity.
Some physicists might then have pushed back against that by inventing
the ether to restore the old familiar notion of absolute time.
Also, collapse models may not even get rid of the parallel Worlds. If
the universe is infinite or is infinite in the temporal direction,
then identical copies of us will exist in an infinite number of
different but similar environments. Collapse will then happen, leading
to a definite outcomes in each sector, but you'll be split among all
the different outcomes in different sectors. The only difference with
the MWI is then that according to the MWI the split must happen, while
according to collapse interpretations, a split may happen depending on
the large scale structure of the universe.
As I see it, the only problem MWI solves is to maintain determinism
contrary to all experience by saying, everything happens but not where
anyone can see it. Which is as if Einstein had discovered QM instead of
Heisenberg.
Brent
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