On 18/11/2017 12:10 am, Bruno Marchal wrote:
On 15 Nov 2017, at 22:26, Bruce Kellett wrote:
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.
You are right. So you might need an experience like Mandel & Co(I will
look at the reference, I guess you see which experience I allude to)
where two distant lasers create a singlet state non locally. That one
has made me doubt that MW could avoid Action-at-a-distance, and some
thought experience by Lucien Hardy too, but eventually, I remain
unconvinced,
You will have to give more precise references. Searching on these names
throws up so many papers that it is impossible to sort out exactly what
you mean here.
because wherever are the actors, the singlet state never describes a
non-local affair, it only predicts the result of the people who will
met at some time.
The singlet state is intrinsically non-local. It actually has nothing to
do with whether people meet or not - it describes a situation which
explicitly violates Einstein's notion of local realism: the state of one
of the entangled pair is not separable from the state of the other
distant particle. Non-separability here implies non-local influence, or
simple non-locality. The attempt to claim that non-separability does not
imply non-locality is mere verbal gymnastics, with no physical content.
Bruce
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