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 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
All 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.
Saibal
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