Quanta: a new theorem beyond Bell's for testing QM

[notFritzArgelander]

I have a headache. I need to come back to this later and perhaps read the original work.

https://www.quantamagazine.org/a-new-th ... d21d14a9ea

[notFritzArgelander]

The original article is paywalled but the abstract is readable:

https://www.nature.com/articles/s41567-020-0990-x

Does quantum theory apply at all scales, including that of observers? New light on this fundamental question has recently been shed through a resurgence of interest in the long-standing Wigner’s friend paradox. This is a thought experiment addressing the quantum measurement problem—the difficulty of reconciling the (unitary, deterministic) evolution of isolated systems and the (non-unitary, probabilistic) state update after a measurement. Here, by building on a scenario with two separated but entangled friends introduced by Brukner, we prove that if quantum evolution is controllable on the scale of an observer, then one of ‘No-Superdeterminism’, ‘Locality’ or ‘Absoluteness of Observed Events’—that every observed event exists absolutely, not relatively—must be false. We show that although the violation of Bell-type inequalities in such scenarios is not in general sufficient to demonstrate the contradiction between those three assumptions, new inequalities can be derived, in a theory-independent manner, that are violated by quantum correlations. This is demonstrated in a proof-of-principle experiment where a photon’s path is deemed an observer. We discuss how this new theorem places strictly stronger constraints on physical reality than Bell’s theorem.

There is a slight problem with the wording of the abstract. The phrase in parentheses referring to a measurement "(non-unitary, probabilistic)" is nonsense. Measurement is unitary with a probability of 1.00... after the fact. Measurement is merely not deterministic just probabilistic. This unfortunate choice of words is unlikely to reflect on the interesting conclusions.

I found the abstract less of a headache than the Quanta article, BTW.

[AntennaGuy]

So quantum mechanics is still weird, hmm? As the great storm of quantum philosophy rages endlessly all about you, hold fast to experimental reality, for it is the final arbiter. And, of course, consider the wisdom of the Psalmists: "...even as I pass through potential valleys of collapsed wavefunctions, I shall fear no measurement! Noether's theorem holds; my ruler and clock, they comfort me."

[notFritzArgelander]

So quantum mechanics is still weird, hmm? As the great storm of quantum philosophy rages endlessly all about you, hold fast to experimental reality, for it is the final arbiter. And, of course, consider the wisdom of the Psalmists: "...even as I pass through potential valleys of collapsed wavefunctions, I shall fear no measurement! Noether's theorem holds; my ruler and clock, they comfort me."

If the inequalities in this theorem hold in the sense that the measurements are objectively consistent for all observers then most Copenhagen interpretation folks, yours truly included, will be happy campers. If the results are subjective I will concede weirdness. The "proof of concept" experiment that folks allegedly did needs to be replicated elsewhere and at different scales. Until that happens, I won't fret.