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
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.



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