On 12-05-2022 22:23, Brent Meeker wrote:
On 5/12/2022 11:27 AM, smitra wrote:
On 12-05-2022 00:44, Brent Meeker wrote:
On 5/11/2022 1:06 PM, smitra wrote:
That's complete and audacious question begging. What you mean by
"real" is "modeled within the SE". There is NOTHING BUT collapse
experimentally; every result recorded in every notebook and every
tape
is evidence of a collapse.
There is effective collapse in experiments we do, but the
experiments nevertheless demonstrate that the fundamental processes
proceed under unitary time evolution.
Except when you measure them and actually get a result.
No, there exist no experiment results that demonstrate that unitary
time evolution is not exactly valid. What you are referring to is that
in experiments we do the wavefunction of the measured system
(effectively) collapses. But, because we also know from all the
experimental results that the wavefunction evolves in a unitary way,
and experiments are ultimately nothing more that many particle
interactions, that either unitary time evolution cannot be exactly
valid or that the collapse during measurement is an artifact of
decoherence where the observer (and the local environment) gets into
an entangled superposition with the measured system. The former
hypothesis lacks experimental support.
"we also know from all the experimental results that the wavefunction
evolves in a unitary way"...until we get a result and then it doesn't.
So does the latter. It's based purely on the absence of a theory of
collapse, beyond, perhaps, decoherence which provides a (sort of)
theory of pointer basis and approach to collapse.
As I wrote in the previous reply, physics does not work in the way you
are arguing here. You always have to formulate a well defined set of
hypotheses first which you can then test with experimental data. There
are plenty of examples where people tried to do test in a supposedly
model independent way and then got results that were not at all model
independent.
In this case, that the wavefunction collapses or at least appears to, is
something that's treated radically different between the CI-like
hypotheses and the MWI-like hypotheses. So, we can consider a class of
MWI-like theories where there is no collapse with CI-like theories where
there is collapse and then consider how they explain all of the
experimental data.
If you do that, then you see that CI-like theories postulate a new
physical mechanism for collapse that's left unspecified that cannot be
explained from the interaction Hamiltonian that one uses. Here I'm
staying within the context of the CI, I'm not introducing any baggage
from the MWI.
In MWI-like theories, there is nothing else than what is described by
the interaction Hamiltonian. The problem here is to get to a better
explanation of ho decoherence leads to the effective classical world.
The former problem is a real physics problem where one depends on a new
phenomena, just like e.g. dark matter in cosmology. It has to exist
according to the theory, but it hasn't yet been discovered yet. But
unlike in case of dark matter where there are multiple independent
observational results that point to its existence, in case of collapse,
you only have the mere fact that in experiments the wavefunction
collapses.
The problems with MWI-like theories is usual business that's seen in
most other theories. Take e.g. superconductivity and we have plenty of
experimental data that's not well explained yet by the theory. But this
does not lead physicists to postulate new physics.
Saibal
Brent
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