On 25-03-2022 22:13, Brent Meeker wrote:
On 3/25/2022 1:06 PM, smitra wrote:
On 25-03-2022 01:29, Bruce Kellett wrote:
On Fri, Mar 25, 2022 at 8:55 AM Brent Meeker <meekerbr...@gmail.com>
wrote:
On 3/24/2022 1:33 PM, smitra wrote:
The account exists in the form of the unitary time evolution of
the state describing the entire system. This is local. It is your
assertion that unitary QM is nonlocal.
It's not local. It's evolving a wave-function which is a non-local
object. I get the feeling you are using "local" in some special
way.
Saibal insists that unitary evolution is local. Everything in QM is
governed by unitary evolution. Therefore everything is local. I have
pointed out one problem with this logic. That is that unitary
evolution depends on the Hamiltonian, and there is no quantum rule
that says the Hamiltonian must be local. The Hamiltonian is
constructed to fit the dynamics of the situation. If the situation is
intrinsically non-local, as for separated entangled pairs, then the
Hamiltonian must be non-local, and the description is non-local.
I explained in the other rely why this is false. The known fundamental
laws of physics are local.
I don't know what that means. Fundmental interactions are local. But
that locality is what makes the bit sequences written by Alice and Bob
in their notebooks statistically independent and hence violating
Bell's inequality which in turn implies some non-local effect. So the
result is non-local by any definition of "local" I'm aware of.
The violation of Bell's inequalities implies a non-local effect in case
of deterministic theories, it doesn't apply to QM assuming that QM is
fundamental. See e.g. this comment by Sidney Coleman:
https://www.youtube.com/watch?v=EtyNMlXN-sw&t=1958s
Saibal
Brent
The other problem with Saibal's account is that it is not peculiar to
many worlds. If all Hamiltonians are necessarily local, then this is
true for single world models as much as for many worlds. So the local
account of the violations of Bell inequalities must be available to
collapse theories as much as to Many Worlds theories. It is obviously
not the case that single world accounts are local. Going to many
worlds cannot make the explanation local.
It's not the case because collapse is not described by a unitary time
evolution based on a local Hamiltonian.
Saibal
I can see the _possibility _of MWI being local if somehow the
multiple worlds evolve thru some interaction where they overlap so
that their weights or numbers are adjust. But I don't see that this
interaction is in the Schroedinger equation. It seems even more
ad-hoc than wave-function collapse.
This is fanciful, since there is no possibility that an appropriate
dynamical model could be devised for such a scenario. I agree that it
is even more ad hoc than wave function collapse. There is no problem
with wave function collapse in epistemic interpretations. The
collapse
just represents the advent of new knowledge. We have no trouble with
the collapse of possibilities in classical physics, or in ordinary
life. The problems people like Saibal see are all in their minds --
the problems with non-locality are not real.
Bruce
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