On Mon, Mar 7, 2022 at 7:41 PM smitra <smi...@zonnet.nl> wrote:
On 04-03-2022 00:17, Bruce Kellett wrote:
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,
If by "common cause" you mean what happens at the formation of the
entangled pair, then your claim is manifestly false. Classical common
cause correlations must always satisfy the Bell inequalities while we
know experimentally that these inequalities are violated.
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.
I don't know why you are obsessed with collapse theories. My question
does not concern such theories. I am asking for an account of the
claimed locality of MWI -- completely independent of any collapse.
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.
That is the question. How does he know this? He is at a spacelike
separation and cannot, locally, know either Alice's polarizer setting,
or her result.. He cannot know that his spin state is opposite,
because he cannot know 'opposite to what?'
So, if he knows what Alice's polarizer setting is,
He cannot know this, so the rest of your statement is otiose.
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.
That knowledge is surely relevant, since Bob does not know either
Alice's setting, or her result. Such a logical possibility has no
bearing on locality or non-locality.
But if collapse is real and the other
Bob does not exist, then there is a real fundamental problem with
this
non-locality.
Again, your irrelevant obsession with collapse theories.
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.
In other words, are you simply giving up on the possibility of an
explanation of these correlations?
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.
You have not demonstrated this -- you have merely assumed it. Zero out
of ten for your explanatory effort. I am still waiting for someone who
actually understands the problem to explain how MWI can give a local
account of these correlations.
Bruce
