On 16/11/2017 1:55 am, Bruno Marchal wrote:
On 15 Nov 2017, at 00:55, Bruce Kellett wrote:
On 15/11/2017 12:47 am, Stathis Papaioannou wrote:
On Mon, 13 Nov 2017 at 8:54 am, Bruce Kellett
<[email protected]> wrote:
I don't think you have fully understood the scenario I have
outlined.
There is no collapse, many worlds is assumed throughout. Alice
splits
according to her measurement result. Both copies of Alice go to meet
Bob, carrying the other particle of the original pair. Since
they both
have now met Bob, the split that Alice occasioned has now spread to
entangle Bob as well as the rest of her environment. So there
are now
two worlds, each of which has a copy of Bob, and an Alice, who has a
particular result. Locality says that Bob's particle is
unchanged from
production, so when he measure its spin, he splits into two copies,
according to spin up or spin down. Since Alice is standing
beside him,
she also becomes entangled with his result. But Alice already has a
definite result in each branch, so we now have four branches: with
results 'up-up', 'up-down', 'down-up', and 'down-down'. However,
only
the 'up-down' and 'down-up' branches conserve angular momentum.
How do
you rule out the other branches?
When you put something in the cupboard and come back later to get
it, why, under MWI, is it still there?
I don't understand the significance of your question. Why wouldn't
things remain stable in MWI? After all, the whole world, as it is,
becomes entangled with the particular branching event.
OK, but not instantaneously. This might be the point where we disagree
in the interpretation of the Non-collapse theory.
I think that the general idea is that the entanglement with the result
spreads at the velocity of light -- inside the forward light cone. This
spread of entanglement does not require that all objects in the forward
light cone have explicitly interacted with the original event. The
mathematics are quite clear on this point.
Bruce
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