a4mula said:
QM does an excellent job of describing the reality of submicro and macro systems. GR does an excellect job of describing the gravational fields of large objects. Are these any less descriptive of reality than classical physics, or any physics for that matter? Just the opposite! They provide a more accurate description.
They provide more accurate predictions of instrumental behavior. But that doesn't necessarily qualify them as descriptions of reality. This is maybe clearer wrt QM than wrt GR.
a4mula said:
There are plenty of mathematical fictions throughout history that have in turned proved to be very accurate descriptions of reality.
Mathematical fictions can be good quantitative (predictive) models -- while at the same time being not very good qualitative descriptions of reality.
a4mula said:
As it stands today MWI does the best job of describing the universe without observers. It's one of a handful of interpretations that are taken seriously by mainstream physics. We know wavefunction collapse happens, that is reality. We do not know the mechanism behind it however. MWI provides this mechanism while violating no known laws of physics, eliminates the need of an observer, and solves multiple paradoxes along the way.
As a quantitative model, MWI does exactly the same thing as standard uninterpreted QM. The rest is just untestable, and conceptually questionable, fiction. MWI doesn't eliminate observers -- at least not insofar as it deals with filters and detectors and data. And, if no unwarranted assumptions about the physical meaning of wavefunctions (and their 'collapse'}, quantum superpositions, etc., are made, then there aren't any paradoxes in the first place.
a4mula said:
As far as closed timelike curves are concerned... I think it's quite premature to state that these are merely mathematical fictions.
GR is on its way out. CTC's will likely be mothballed with it.
a4mula said:
Are you going to claim that black holes are mathematical fictions as well?
There's observational evidence of their effects. Also, black holes, like white dwarfs, neutron stars, etc. don't require the GR block universe, spacetime geometric model. Black holes, etc., can exist in an evolving, transitory universe -- where the spatial configurations corresponding to the past really don't exist other than as subjective recollections or objective records of them. But, CTC's can't exist in a transitory universe (which I think is a more accurate description of the real one that we are part of).
a4mula said:
CTCs have long been predicted, not by just one or two theories, but by many. They show up in equation after equation and as of yet we've been unable to find anything that seems to dispute their existence.
Or anything to confirm their existence. CTC's are an untestable prediction, afaik. So that leaves us with a mathematical construction that has no physical basis.
We also don't see advanced waves, or broken stuff spontaneously reassembling itself, etc. -- and I think a better approach than taking these things as physical possibilities simply because they're allowed or appear in one model or another is to assume that they're precluded by the physical dynamics which govern our universe.
Quantum experimental phenomena and QM (even though it shouldn't be taken as a description of reality because the extent to which the formalism corresponds to an underlying physical reality is unknown) provide indications that physical reality is fundamentally wavelike. In my view, current physics is a necessary simplification of a fantastically complex system of wave interactions in a fantastically vast hierarchy of particulate media (the particles being bound wave structures) arising from a few, and maybe just one,
fundamental wave dynamic(s).
a4mula said:
While you seem to have some disdain for the mathematics involved in the process it's a necessity in Scientific Method.
Disdain for the mathematics involved? What gives you that idea? I love mathematical models. But there's usually an important difference between mathematical models and 'descriptions of reality'.
The normal procedure is to develop mathematical models that are consistent with the current standard theoretical structures and also fit the data, and then worry about the physical conceptual (qualitatively descriptive) issues as they arise. This approach is somewhat efficient, but has led to a situation where there isn't a unified conceptual framework.
But, I think that eventually this will happen. And when it does, then I think that backward time travel will be theoretically, not just practically, prohibited.
It seems to require that second viewing. One loop and it all becomes crystal clear. 
