Thanks very much for the topic Barry.
The Bell interview made very interesting reading - which then lead to a lot of other good stuff.
Re QM, FWIW my thoughts are:
There appears to be overwhelming experimental verification of QM as a predictive tool - it seems that it always gets the right answers.
https://www.forbes.com/sites/chadorz.../#79ef02e84046
My reading is that Bell's major advance was to resolve the philosophical issue of whether there is an underlying local realism at quantum scales (there isn't) and to show how that conclusion can be verified experimentally. Seems to me to be an astonishingly significant outcome - when you get to the bottom of Alice's rabbit hole, objects do not have definite properties and there can be instantaneous interactions over arbitrarily large distances - and you can prove it! Recent tests of QM (via Bell's inequality) appear to have plugged all of the possible loopholes that might allow an underlying local realism. eg, >10sigma rejection of local realism in
https://arxiv.org/pdf/1805.04431.pdf. Entangled photons (and atoms etc) really do behave in a correlated way, even when they are widely separated (in QM parlance, measurement of the state of one particle instantly determines the state of its separated pair).
Re the need for QM in our hobby, agreed that Maxwell's equations fully describe what happens to light on a lens. However, I think that QM concepts are required to explain why stars do not rapidly disappear in violent flashes of UV, X and gamma rays (the UV catastrophe) or why our photon detecting cameras work the way they do. Classical physics could not do that.
Re quantum encryption/computing being with Santa and the Goblins...I was surprised to find that one can buy a real working commercial 20km comms system that is secured by quantum cryptography (entangled photons).
http://qubitekk.com/security/. You could also buy a specialised 5000 qbit quantum computer if you had a major physics lab or a bank
https://www.dwavesys.com/media-cover...antum-computer. This stuff is already working here and now and is mature enough to start being used on real world problems
https://www.volkswagen-newsroom.com/...computers-5507 and
https://www.ibm.com/blogs/research/2...fur-batteries/. If you want hands on, IBM offer on-line access to a 20 qbit general purpose quantum computer and to simulators that can be used to explore algorithms.
The simple crossed polariser experiment, mentioned earlier, is a refreshing reminder that the real world is not intuitively comprehensible at the level of the very small - something happens with the third polariser that cannot be explained in any sensible way - it makes it quite clear that physics at the quantum level really is very weird.
Anyway, thanks for the topic - really interesting and thought provoking.
Cheers Ray
edit: More interesting stuff: appears that entanglement can be demonstrated at larger scales:
https://www.pnas.org/content/116/45/22413
and there is also a set of images showing entangled photons in action
https://phys.org/news/2019-07-scient...e-quantum.html