On Mon, Dec 2, 2019 at 8:08 PM Bruno Marchal <marc...@ulb.ac.be
<mailto:marc...@ulb.ac.be>> wrote:
On 29 Nov 2019, at 00:50, Bruce Kellett <bhkellet...@gmail.com
<mailto:bhkellet...@gmail.com>> wrote:
On Fri, Nov 29, 2019 at 1:27 AM Bruno Marchal <marc...@ulb.ac.be
<mailto:marc...@ulb.ac.be>> wrote:
On 26 Nov 2019, at 22:39, Bruce Kellett
<bhkellet...@gmail.com <mailto:bhkellet...@gmail.com>> wrote:
On Wed, Nov 27, 2019 at 12:27 AM Bruno Marchal
<marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>> wrote:
On 25 Nov 2019, at 22:53, Bruce Kellett
<bhkellet...@gmail.com <mailto:bhkellet...@gmail.com>>
wrote:
Because, the wave-function itself is non-local -- it
contains entangled particles that are widely separated
in space. That is the definition of non-locality!
I am not sure. I use “non-locality” for “FTL physical
influence”.
That is just an abuse of language. Non-local means "not
local", i.e., not all in one place.
Then even Newton Universe is non local.
Yes Newton was aware of this.
Some attempt has been made to replace the term "non-local"
with the term "non-seperable”.
Yes, notably d’Espagnat. It avoids the confusion with the
Eisnsteinian non-locality, which requires FTL (cf the “spooky
action at a distance”), which must exist in QM + the
assumption of a unique universe.
I think we can all agree that the singlet wave function is
non-separable -- it cannot be written as a simple product of
two terms, one referring to each particle.
Yes, we agree on this.
I maintain that it is also non-local, in that the two
particles are at different locations (locales). Non-local
can have no other meaning in ordinary linguistic usage.
I invite you, and Alice, and I give you an envelop to each of
you. You are told that one contain a piece of paper with O
inscribed on it, and the other with one. Then you go in
different galaxies, say, and open it. Once you see 0 (res. 1)
you know that Alice will see 1 (res. 0). This seems non local
in your sense, where most would agree that in this case,
there is no “non-locality” issue. What I claim is that in the
Everett theory, all non-locality are of that type.
That non-loclality has a common cause explanation. Like
Bertlmann's socks, there is no mystery here. The problem is with
entangled systems, where non-separability means non-locality that
has no common cause explanation, even in many-worlds theory.
I doubt this. The MWI reduces the non-separability of the
probabilities into an equivalent with Bertlmann’s socks, still
keeping the violation of Bell’s inequality justifying the
appearance of non-locality.
The devil is in the detail. And you have still not provided any detail.
In the MWI, some particles can be entangled but without
implying any possible FTL when we do measurement on
them, except from the local point of view, due to our
ignorance of all terms of the wave. It means simply that
Alice and Bob belongs to the same branch of history/reality.
The trouble with this hope is that it no local account of
the EPR correlations been realised in any coherent
mathematics. Bell's theorem rules it out: no local hidden
variable account of the EPR correlations is possible in any
theory, whatsoever. It is a no-go theorem; it proves a
negative -- something is impossible. Many-worlds does not
subvert Bell's theorem.
That is right. But the violation of Bell’s inequality entails
FTL only when one world is assumed, with well defined outcome
for all measurement, or put in another way, assuming a unique
reality, with one Bob and one Alice, but Bell’s reasoning
does not prove FTL influence in The many-worlds, where all
outcomes are obtained, and propagate between diverse Alice
and Bob locally, leading to the apparent violation of Bell’s
inequality, but without FTL.
Bell did not assume a collapse. His is a mathematical result,
where the only assumption is locality. As usual, if you think
there is a local explanation of the EPR correlations in
many-worlds, then produce it.
We differ only on the way we interpreted the wave and the worlds.
The singlet state is … local! It does not entail any correlation
between the Alices and the Bobs. It enforces only that the Alices
and Bobs can meet only their corresponding correlated partners,
among the infinitely many Alices and Bobs (most of them being not
accessible from each others).
The singlet state is non-separable, and hence non-local when Alice and
Bob are separated. The rest of you comment here is without meaning.
You have to flesh it out, and your reluctance to do so convinces me
that you cannot. You are just hoping for a miracle.
I think it is becoming generally accepted in the physics
community that the entangled state is intrinsically
non-local: acting on one part of it affects the rest, even
across the entire universe.
That would mean some FTL actions, but I very much doubt this.
No, there is no need of FTL. For example, in the third (2011)
edition of his book 'Quantum Non-Locality and Relativity',
Maudlin shows that Flash GRW theory, as developed by Temulka,
gives a perfectly relativistic account of the EPR correlations
without any FTL action.
This astonishes me. If you have a link I could try to see if this
makes sense, but, to be sure, I am not enthusiast at all on the
GRW theory, which is new QM theory. If some measurement affects
the rest of the Universe instantaneously, I think that imply FTL
(without signals, but still with a physical influence).
I only know this from Maudlin's books. There is a detailed account in
his recent book, "Philosophy of Physics: Quantum Theory" (Princeton,
2019). The paper that Phil referenced: Esfeld and Gisin
(arXiv:1310.5308) contains a summary and discussion, even though those
authors are not convinced by the theory.
I must admit that Flash GRW is not an approach that I find convincing
either. The ontology of this theory is the flashes themselves, the
wave-function is not part of the ontology, so the collapse is entirely
epistemic, and just like the "collapse" in classical probability
theory. It works, but may not be convincing to everyone, since the
ontology is remarkable thin!
The real problem is, as ever, that despite many promises, many-worlds
theory does even less well in that it offers nothing in the way of an
explanation. Maudlin's recent book discusses many worlds, but he
concentrates on the problems with this idea, and essentially is not
convinced that many-worlds makes sufficient sense in its own terms to
provide an explanation for anything. Sean Carroll, in his recent book
"Something Deeply Hidden", also evades the question. His discussion is
on pages 104-105. He states that Bell assumed "that measurements have
definite outcomes". Essentially, this is the assumption of
counterfactual definiteness that has often been proposed.
