From: *Bruno Marchal* <[email protected] <mailto:[email protected]>>
On 11 Aug 2018, at 02:49, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
From: *Bruno Marchal* <[email protected] <mailto:[email protected]>>
On 9 Aug 2018, at 14:03, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
Without collapse and FTL potential, or FTL (non-local) hidden
variable theory, how do you interpret the singlet state?
That is actually a rather strange question. How do you think I
might interpret the singlet state? I think that I have been talking
about it here for long enough for you to have worked it out. The
singlet state is a non-separable state that is symmetric under
rotations about the axis between the particles. However, that
symmetry will generally be broken by any interaction with one or
other of the constituent particles.
But it is here that I suspect you introduce some collapse.
The interaction with one particle reduces the symmetry of the
non-separable state so that it becomes separable.
Locally, and from the observer viewpoint, not in the big picture, as
nothing is ever reduced. The superposition does not disappear.
There is still a superposition, even though it has decohered and the
separate results are in FAPP orthogonal branches. But the superposition
is not the issue -- that relevant fact is that the measurement has
destroyed the rotational symmetry of the state.
You might call this a "collapse" if you wish, but this is an
epistemological collapse, not an ontological one. It is the nature of
the state representing one's knowledge that changes (the old state
"collapses" with the advent of new knowledge).
Then I agree. That makes things local, and personal somehow. You get
close to “my” version of the many-mind account.
I doubt it. There is no "bigger picture" in which the symmetry is preserved.
But that is purely epistemological, and does not involve any FTL
information transfer.
That’s my point.
But you apparently still do not accept that the symmetry of the state is
destroyed, even without physical FTL. The wave function is not a
"physical" object -- it can easily change instantaneously, just as
probabilities change on the advent of new information.
It is just as if the probability that your horse will win the race
"collapses" when you find out, after the race has been run, that it
came last!
In particular, the symmetry is broken by the imposition of a
directional magnetic field, as in a Stern-Gerlach magnet used to
measure the spin component of one of the particles in the direct
defined by that external magnetic field.
The singlet is strongly non-separable, so this external interaction
with one of the constituents is instantaneously felt by the other
component particle.
How could this be verified?
It is verified by the Freedman-Clauser and Aspect experiments (and
many other more recent experiments).
This tests only the non separability issue. Not the existence of a
physical FTL in our branch. That follows from what you say above.
The non-separability *is* the non-locality. Do you not yet understand that?
Any verification possible will need further interaction, and we can
see only the branche of the universe our own result have spread on.
The verification comes from the results of remote experiments -- and
those results do not change during the time it takes for the
experimenters to come together to compare findings.
Those results makes just Alice and Bob knowing which branches they
belong too. The non-locality is a global notion on the full
wave/multiverse,
That has never been demonstrated. It is a pious hope of yours, but you
always shy away from proving it.
but the FTL are needed only if we associate the mind on Bob and Alice
to the same branche, which has no meaning for me once they are space
separated.
You might not accept that they can be in the same branch, but that does
not mean that it is not a proven fact.
But we know we disagree on how to interpret the singlet state in the
MW frame.
That non-local influence is the essence of the non-separability of
the state -- it is a unit, and any interaction with a part is an
interaction with the whole.
That looks magical to me, and as I said, I am not sure this can be
verified. Aspect-like experiment do not verify this for sure.
It might look magical to you, but that is because you have not really
accepted the true weirdness of quantum theory. The Aspect-like
experiments certainly do verify this -- why else do you think that
these experiments were performed?
To verify QM’s prediction. After Aspect, the choice is between
determinacy+locality+many-worlds or one world + 3p indeterminacy, 3p
physical FTL.
Determinism has nothing to do with it. Aspect and Bell rule out
deterministic local theories, so non-locality is the only possibility.
Many-worlds does not change that. Both Bell's theorem and Aspect's
results are true in many-worlds as in any other interpretation of QM.
Don't you understand that that is why most commentators from the
many-worlds perspective try to show that Bell's theorem does not apply
to many worlds? They know that if it does, then many-worlds is as
non-local as any other interpretation. Of course, they fail in their
attempts to deflect Bell's result. In fact, some of the attempts and
failures are almost farcical in their silliness, but I suppose you can't
see that, either.
Bruce
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