I have recently been involved in acrimonious discussions in a Google group, https://groups.google.com/g/bell_quantum_foundations, devoted to Bell’s theorem and the interpretation of quantum mechanics. One of the group members, Bryan Sanctuary, insists that two particles leaving a source cannot remain entangled. He claims in preprints in a sequence of recent blog posts that the EPR-B correlations cannot remain valid once the particles are separated. Here is a link to one of the posts, http://blog.mchmultimedia.com/2022/05/09/hyper-helicity-and-the-foundations-of-qm/. At the same time, he claims that the EPR-B correlations do have a local and realistic interpretation once one introduces a hidden, quantum property which he calls hyper-helicity. He believes that in this way all notions of non-local collapse and weirdness can be banished from quantum mechanics. Another participant, Alexey Nikulov, also thinks that conventional quantum mechanics is wrong, and disbelieves in non-locality and collapse.
A small problem consists in figuring out what actually is Bell’s theorem. A long essay by Sheldon Goldstein (2011) on “Scholarpedia”, http://www.scholarpedia.org/article/Bell%27s_theorem, makes it clear that Bell twice quite radically changed his thinking, so in fact, one could say that there are three Bell theorems. The essential mathematics changed from the first to the second, and the physical motivation behind his characterization of a “local hidden variables model” evolved both in the first change and in the second change. The theorem is always the same, that a local hidden variables model cannot reproduce certain quantum mechanics predictions, but its assumptions and interpretation have matured.
I have started writing out some notes, maybe they will become a whole paper, to make it clear that “collapse of the wave-function” is an interpretational optional extra, not needed in order to apply quantum mechanics in practice. No interpretation of what is going on behind the scenes is necessary if one’s purpose is to describe nature. An interpretation might be useful if it helps one to understand nature. One must realize that it is possible that understanding nature is something which will forever go beyond our poor facilities. That is not to say that the drive to gain understanding isn’t the true drive behind doing science. Like democracy and justice, understanding is an ideal which we have to continually renew and re-affirm.
That does mean that in introductory expositions it should be clearly labelled as a lie for children.
The usual colourful language involving the non-local collapse of the wave function can be thought just to be a description of a useful computational tool, not a description of physical changes to something existing in physical reality. The only thing assumed to exist are measurement outcomes, and the theory allows us to compute probability distributions of their outcomes, also in complex, composite, sequential, experimental set-ups. One can compute what one needs to know by pretending that the wave function collapse as suggested by the von Neumann-Lüders extension of the Born law is somehow real. One gets the right answer, as directly as possible. There is, however, no need to think of wave function collapse as being something physical (and necessarily non-local). Such thinking is an optional extra. Some people find it distasteful. Tastes differ. I think it can be usefully thought of as one of those lies for children which need to be seen in a different light as one gains maturity and knowledge.
We are all children! Learning never ends!
The second purpose is to write out the mathematical content of Sanctuary’s claims concerning hyper-helicity. Sanctuary feels that his interpretation of his mathematical formalism will revolutionize our understanding of quantum entanglement. Clearly, he has a long way to go, but I hope my own struggle to understand what he is doing will be helpful to others, if not to him.