On 11/17/2017 4:23 PM, Bruce Kellett wrote:
On 18/11/2017 10:43 am, [email protected] wrote:
On Friday, November 17, 2017 at 3:18:39 PM UTC-7, Bruce wrote:
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] <javascript:>> 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.
But as Brent claims, and I think he is correct, there is a basis in
which the singlet state is a eigenfunction. In that basis, the
obvious non locality may not be so obvious, if indeed it exists. AG
I think you might have misunderstood Brent. The entangled singlet
state is not an eigenfunction of any operator. It has a definite spin,
but there is no local operator that corresponds to this.
No/*local*/ operator. But in theory there is a basis in which the
singlet state is an eigenstate. In fact it's the eigenstate of our
preparation process regarded as an operator. The operator to project
onto this eigenstate is non-local and would involve interacting with
both particles so as to produce 1 if their spins were opposite, 0 if
not, but (quantum) erase which way the spin pointed.
Brent
The entangled singlet consists of two particles which exist in
different subspaces of the wider configuration space. The particles
are not separable, and the singlet state requires both of them. Hence
the non-locality.
Bruce
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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