The ontological models framework distinguishes ψ-ontic from ψ-epistemic wave- functions. It is, in general, quite straightforward to categorize the wave-function of a certain quantum theory. Nevertheless, there has been a debate about the ontological status of the wave-function in the statistical interpretation of quantum mechanics: is it ψ-epistemic and incomplete or ψ-ontic and complete?I do not see how this question makes any sense. The wave function is not directly observable. It is useful for making predictions. What sense is there in wondering whether or not it is real?
Bell's theorem shows that psi cannot be epistemic in the sense that it shows our knowledge about an underlying local hidden variable theory. But it could still encode our knowledge about the physical state.
The paper also talks about whether psi is statistical. Agaikn, this makes no sense. All physical theories are statistical in the sense that you can run multiple experiments, and compute statistics on the predictions and outcomes. Quantum mechanics is not much different from classical mechanics in this way. All the theories give error bars on predictions, if you do them right.
Supposedly the PBR Theorem proves that psi is ontic. This is very misleading, at best. If I release an electron from my lab, its wave funciton will soon be miles wide. Does any think that the ontic reality of that election is miles wide? No, that is absurd. Only our uncertainty is miles wide, because we don't know which way the electron went.
The PBR paper was originally submitted under the title, "The quantum state cannot be interpreted statistically". It is baffling how anyone could think that they proved something so absurd. Everything can be interpreted statistically. How could it not be? When the paper was published, the editors forced them to change the title to "On the reality of the quantum state". Of course the paper cannot prove anything about reality either.
The Schroedinger Cat thought experiment was supposed to dispose of the idea that the wave function is ontic. The cat is not really half dead and half alive. The wave function predicts probabilities consistent with observation, and that is all. Schroedinger and Bohr thought that this was obvious.
A lot of people seem to believe that the Copenhagen interpretation requires believing in a cat that is a superposition of dead and alive. Wikipedia says so. But it also says that Bohr himself did not, and believed that something like decoherence would irreversibly put the cat into the dead state or the alive state, even before anyone opens the box.
Here is a recently-released short video on Max Tegmark - Many Worlds of Quantum Theory. I wonder if these physicists realize how ridiculous they sound when they gave layman explanations.
He says he believes that the many worlds are real, because we see electrons being in two places at once in the lab. But no one has ever seen an electron in two places at once. The double-slit experiment can be interpreted as an electron going thru both slits, but that is just a wave property of an electron. And even if an electron can be in two places, and humans are made of electrons, it does not follow that humans can be in two places.
Never mind the details. Many worlds theory is an absurdity. He says these worlds are real, and there is no evidence for them whatsoever. Listening to him is like going to a comic book convention and watching someone, dressed in a costume, ramble about some fantasy world as if it were real.
Tegmark ends by saying that many-worlds could be disproved if quantum mechanics were disproved. He does not even admit the obvious possibility that quantum mechanics is correct and many-worlds is not.
Sabine Hossenfelder has a new lecture on The Other Side Of Physics (TEDxNewcastle). It is hard to take anything she says seriously, once you realize that she believes in superdeterminism. She talks about Physics as a tool for answering questions, but that is not true under superdeterminism. That teaches that experimental results cannot be believed, because the outcomes could have been forced by a conspiracy dating back to the Big Bang. In particular, it says that all the quantum experiments could be fake, and that we really live under classical mechanics.
In particular, she argues that the correlations of the Bell test experiments are all wrong because they are artifacts of the experimenters failing to properly randomize the input data, and they always fail because of mysterious constraints.
She also says that Eintein's special theory of relativity showed that there is no such thing as "now". This is because when we see or hear something, it takes time for the signals to reach our brains.
Then she rambles about multiverse theory being ascientific, because the scientific method cannot be applied to it. But surely superdeterminism is even worse, and is unscientific, as it says that the scientific method does not work.
She says that information cannot be destroyed. Seems like more unscientific nonsense to me.
There are certains ideas of Physics that are so outlandish as to discredit anyone who promotes them. I include: many-worlds, superdeterminism, retrocausality, simulation hypothesis, and action-at-a-distance.
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