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.

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

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.


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