On 11/13/2017 1:40 PM, Bruce Kellett wrote:
On 14/11/2017 2:07 am, Bruno Marchal wrote:
On 12 Nov 2017, at 23:05, Bruce Kellett wrote:
What really annoys me is the continued claim that many worlds
eliminates the need for non-locality. It does not, and neither Bruno
nor anyone else has ever produced a valid argument as to how many
worlds might restore locality.
But nobody has proved that there is non locality in the MWI. EPR-BELL
proves non-locality apparant in each branch, but the MWI avoids the
needs of action at a distance to explains them. Once Alice and Bob
are space-separated, their identity are independent. It makes no
sense to talk of each of them like if they were related, (unless you
correlate them with a third observer, etc) If they do measurement,
some God could see that they are indeed no more related, but if they
decide to come back to place where they can compared locally their
spin, they will always get contact to the corresponding observer with
the well correlated spin. The independent Alice and Bob will never
meet because they can't belong to the same branch of the multiverse,
by the MWI of the singlet state. So Mitra is right.
Although Bertlmann's socks are tyically not working for Bell's
violation in a MONO-universe, it works again in the MWI, applied in
this case to the whole singlet state.
Bell has proved non-locality in MWI, every bit as much as in each
branch separately. You appear not to have grasped the significance of
the scenario I have argued carefully. Alice and Bob are not space-like
separated in the scenario I outlined. Alice and Bob are together in
the same laboratory when the second measurement is made. They are
necessarily in the same world before, and branch in together according
to Bob's result. Your mumbo-jumbo about them only being able to meet
in appropriate matching branches does not work here, because they are
always in the same branch. And there is no reason to suppose that
their results in some of those branches do not violate conservation of
angular momentum.
It's that last point I don't understand. Why isn't conservation of
angular momentum a condition in every world. It's something separate
from QM. I'd say there is non-locality even when Bob's measurement is
time-like because there is correlation with no physical causal link.
The "common cause" of conserved angular momentum is not an explanation
because that doesn't work in the space-like case and there's no reason
to suppose QM is different in the two cases.
Brent
Bruce
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