On 25-03-2022 23:01, Bruce Kellett wrote:
On Sat, Mar 26, 2022 at 6:37 AM smitra <smi...@zonnet.nl> wrote:
On 24-03-2022 22:57, Bruce Kellett wrote:
OK. I see now that your insistence that QM is local is based on
dogma,
rather than logic. Your claim is that the unitary time evolution
in QM
is local, therefore QM is a local theory, regardless of anything
else.
But that position relies on another hidden assumption. The unitary
time evolution of QM depends on the Hamiltonian. The Hamiltonian
is
not given by the theory; it is constructed according to the
details of
the system one is attempting to model. Generally, one is modelling
local systems, so one uses a local Hamiltonian and the time
evolution
is local. But this is by no means necessary. One could always use
a
non-local Hamiltonian, then the time evolution would not be local.
One can indeed write down non-local effective Hamiltonians, but the
fundamental laws of physics are strictly local.
God told you this, did he? If one needs non-local physics to describe
certain experiments, then locality is not universal.
The Standard Model is local. If you can experimentally verify that for a
certain physical system the Standard Model (extended to take into
account finite neutrino masses) is not adequate, then you'll win the
Nobel prize for that discovery. We know that the Standard model has to
fail when quantum gravity will become important. But we cannot probe
this regime experimentally, and for the sort of things we're discussing
here, it's not relevant.
This is the situation with the entangled spinor case. The state
vector
is non-separable and does not specify any particular separation
for
the two entangled particles. If one wants to continue to treat
this as
a single system even when the particles are far apart, one must
use a
non-local Hamiltonian.
The fundamental Hamiltonian that also describes how the entangled
state
was created, is local. It's only when you put in the entangled
spinor
state in by hand that you get an effective non-local Hamiltonian.
Where did you get the idea that the entangled spinor state was "put in
by hand"? Sure, the entangled spinor state was created locally, but it
is intrinsically non-local in that it refers to arbitrarily separated
states in terms of a non-separable wave function. The entanglement is
created at some point then particles move apart, but this separation
preserves the entanglement, and if you are to understand the results
of measurements on this entangled pair, you must consider it as a
unified system, not as two separated and independent parts. That is,
the system is intrinsically non-local, and you will never be able to
understand a non-separable system in terms of independent parts. Do
you not understand what "non-separable" means?
What matters is the time evolution step by step proceeds in a manifestly
local way. The entangled spin system is created locally, the two
particles travel to the locations of Alice and Bob. Alice and Bob and
their polarizers considered as large collections of particles interact
locally with the spins. While you then do find correlations that exhibit
nonlocal properties, there is then a local account of how these
correlations arise, namely the time evolution via the Schrodinger
equation with a manifestly local Hamiltonian. Such a Hamiltonian is
always available because the well established low energy physics won't
violate the Standard Model.
Saibal
Bruce
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