On Thu, Oct 3, 2019 at 7:08 PM Bruno Marchal <marc...@ulb.ac.be> wrote:
> > On 1 Oct 2019, at 19:37, 'Brent Meeker' via Everything List <
> everything-list@googlegroups.com> wrote:
> > On 10/1/2019 4:38 AM, Bruno Marchal wrote:
> >> Right. Then the non locality has disappeared from the wave equation at
> the start.
> >
> > No, Bruce's point is that it must be present at the start. Otherwise
> Bell's inequality couldn't be violated.
>
> Bruce agree that there is no FTL action, that is locality. The non
> locality is in the perspective view. It is not a global truth, as that is
> obvious if you agree that the wave function evolution is only a rotation in
> some space. Rotation are typically local, even in abstract spaces (which in
> Everett and with mechanism are the real thing).
> Now, with “one physical universe”, that non-local perspective implies some
> FTL action.
>
I think you have missed the point, Bruno. The wave function itself is
non-local. Consider the entangled singlet state that we have been talking
about:
|psi> = (|+>|-> - |->|+>)/sqrt(2).
The kets in the tensor product refer to different particles, with arbitrary
separation in space-time. But this is a single state. Because it is
non-separable, and refers to different spacetime locations, it is
intrinsically non-local. You can rotate it as much as you like in Hilbert
space, but you will never remove the non-locality. That is the way it is --
it will always refer inevitably to two separate spacetime locations.
As Wallace reports Deutsch to have said: "quantum theory is a theory of
local interactions with non-local states." So with EPR correlations, the
state is intrinsically non-local but all the measurement interactions are
local. The trouble is that, because of Bell's theorem, there is no local
causal explanation of the correlations -- they are evidence of the
non-locality of the state. And there is no FTL action -- that would be a
local hidden variable causal explanation, and Bell rules that out.
Bruce
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