On Wed, Nov 27, 2024 at 4:42 AM smitra <[email protected]> wrote:
On 25-11-2024 23:21, Bruce Kellett wrote:
On Tue, Nov 26, 2024 at 12:16 AM smitra <[email protected]>
wrote:
On 24-11-2024 05:04, Bruce Kellett wrote:
If QM were intrinsically local, then you would be able to give
this
local account of the correlations.
You are manifestly unable to do this.
It's obvious from the time evolution specified by the local
Hamiltonian.
You have tried this approach before. You seem unable to realize
that
that is just a restatement of your position. And it is that
position
that is in question. Restating your conclusion is not an argument
or
an account of anything.
You are disputing a triviality, namely that we have a unitary time
evolution specified by a local Hamiltonian:
U(t) = exp(-i H t/hbar)
At least that's what you are claiming. What you are really doing is
that
you play hide and seek in the complexity of this. Your real bone is,
of
course, with the idea that time evolution is unitary and that there
is
no collapse. Obviously, the only plausible reason QM could be
non-local
is if there is a real collapse. If everything always stays unitary
with
the unitary transform specified by a local Hamiltonian then there is
no
collapse, and everything always stays local. That doesn't mean that
you
can't have states with non-local properties, what it means is that
whatever happens always follows from applying local laws. Sol,
non-local
features can be explained using common cause effects propagated by
local
unitary dynamics.
You appear to be veering towards the position exemplified by Wallace
in his book "The Emergent Multiverse", where he says that in
Everettian quantum mechanics interactions are local, but states are
nonlocal (p. 310). If you do take such a position, you have to
acknowledge the importance of the nonlocality of the entangled state.
Going on about unitary dynamics is of no help to you in understanding
this.
You made the extraordinary claim that Bell proved that QM
is non-local, which is plain nonsense.
No, it is not nonsense. Bell's theorem, which depends only on the
assumption of locality, shows that the correlations from entangled
particles must satisfy certain inequalities. These inequalities are
violated by standard quantum mechanics, and also by experiment.
The challenge is to explain these violations. And that is possible
only by invoking nonlocality. If you think you can explain the
experiments without invoking nonlocality, go ahead. But no one has
ever done this.
Yes, it invokes unitary QM with the unitary time evolution specified
by
a local Hamiltonian. This implies a MWI scenario, but not per se
with
all the baggage of splitting worlds that are supposed to split in
independent ways. You end up with different sectors that are
entangled.
So, you are invoking the nonlocality of states that Wallce refers to.
That is all very well, but that is not a detailed explanation of how
this works. Wallace can't give a detailed explanation either, because
that would involve nonlocal dynamics, but he thinks many-worlds allows
you to avoid this. He is mistaken, of course.
Bell's theorem doesn't prove that QM is non-local. If that were the
case, then this would be just another of QM that would be proven in
any
QM textbook, and it would make unitary QM specified by a local
Hamiltonian inconsistent. The whole debate about e.g. black hole
information loss wouldn't happen in that case. The fact that this is
a
hot topic in theoretical physics proves that you
don't really understand the subject matter you are debating here.
It's
true that QM could be non-local but that's not implied by Bell's
theorem. If you were right on this point, then that would imply that
all
theoretical physicists get this wrong and you are one of the few
people
who knows better. So, clearly not a matter of "Not everyone gets it
right", rather that everyone else but you is getting it wrong, and
that
makes it appropriate to invoke an argument from authority pointing
that
out.
You are talking a lot of nonsense. I refer you to a paper by Brunner
_et al._, Rev Mod. Phys. 86 (2014) pp.419-478.
This is also available at arxiv.org/abs/1303.2849 [1]
The abstract states "Bell's 1964 theorem, which states that the
predictions of quantum theory cannot be accounted for by any local
theory, represents one of the most profound developments in the
foundations of physics."
Brunner _et al._ go on to derive the CHSH (Clauer-Horne-Shimony-Holt)
inequality using only local dynamics, and prove that this inequality
is violated in conventional QM, as well as in many experiments. This
proves that quantum mechanics is intrinsically nonlocal. (If you like,
it demonstrates that nonlocal states are intrinsic to the theory.)
And b.t.w. if there is a Bell's theorem purely about unitary QM that
doesn't invoke hidden variables, you could just state it right here.
I don't prove Bell's theorem here, but I have referred you to Bell's
original papers, and also to the review article by Brunner et al.,
above. If you actually do the research for yourself, you can see that
many authors agree with what I have been saying. You are the one that
is out on a limb.
You
didn't do that and made the counterclaim against me when I pointed
out
that Bell's theorem is about inequalities for certain correlations
satisfied by local hidden variable theories, which is common
knowledge.
No according to the original sources: hidden variables do not come
into it.
And I made the remark that it's then a theorem about local hidden
variable theories, not QM, so it's relevance to QM is limited to the
ideas that QM might have an underlying hidden variable theory. You
are
disputing this only on your say so, so basically an argument from
authority where the authority is you, not even references to the
works
other experts in the field.
I have given you references here, and I have referred you to Bell's
original papers before.. But you do talk an awful lot of nonsense.
