Undergrad Have We Got What Bohr Thought Wrong

[bhobba]

Feynman once said something along the lines of that when scientists talk about the history of science its a version handed down to them by their science teachers or from science textbooks. This may not be the same as what a professional historian of science says. As an example of this see the following paper:
https://www3.nd.edu/~dhoward1/Copenhagen Myth A.pdf
I have never understood complimentary personally. But if it's as suggested in the paper actually entanglement, and its just Bohr's well known obscurity that 'hides' his true intent, then I am with Bohr in that I think entanglement is the central, issue, mystery, whatever you want you call it of QM. Its a very common misconception that Einstein did not believe in QM, hated its probabilistic nature, you know all the stuff you read in popular accounts. This of course is false, his views changed over time, and another example of the popular account of the History Of Science being wrong. Fortunately Wikipedia gives a much better account:
https://en.wikipedia.org/wiki/Bohr–Einstein_debates
We see here that during Einsteins 4th stage he too had reached the conclusion that what really worries him was what entanglement suggested - realism in the common-sense version does not hold, and because of that QM must be incomplete. I have written before I think all our current best theories eg the Standard Model are incomplete being only valid to about the Plank Scale so is incomplete. Maybe Bohr and Einstein were closer in their views than some think. Bohr wasn't particularly worried about the implications of entanglement, in fact he thought it the central feature of QM. Einstein eventually came around to thinking entanglement was also the central feature - but its implications worried him deeply.

I have a certain mathematical bent in my view of things - for entanglement, even though I have posted it before, I find the following interesting:
https://arxiv.org/abs/0911.0695. It is my personal view on the issue - it's what separates classical from quantum physics. And I do acknowledge some of the very knowledgeable posters on this forum think this information view of QM needs care in understanding it correctly.

Thanks
Bill

 

[DarMM]

Just to be strictly clear (and this is pure pedantry as such) in the correlation hierarchy entanglement is strictly weaker than nonclassical correlations. Entanglement refers to the existence of non-seperable pure states. This can occur in epistemically restricted classical theories.

What cannot occur is violations of Bell's inequality, i.e. Non-classical correlations. It and contextuality imply each other so we might say the crucial feature is Non-classical correlations and Contextuality since they are linked.

Of course by entanglement I know you mean Bell inequality violations, so there I would agree. this is because it seems to be the one aspect of QM you cannot replicate with any kind of classical theory. You might like the paper of Renner and Ekert here where they derive randomness from individual systems from non-classical correlations:
https://www.nature.com/articles/nature13132?draft=journal
i.e. the systems are too correlated for each to be deterministic

 

[DarMM]

Regarding the actual paper linked it's well known and the general agreement among historians of science is that Howard is correct in that the "Copenhagen Interpretation" is a anachronism projected back onto the 1920s and 1930s by Heisenberg in the 1950s to make it seem like there was some common and clear set of ideas about QM in the early days.

There's still a bit of discussion about what Bohr meant about "no independent reality" for the device and atomic system. With some saying he meant entanglement and others saying he meant that quantum events represented by projectors $E$ represent device-system interaction events. A very often cited paper along the latter line (which uses Howard's paper) is this one:
https://arxiv.org/abs/0804.1609
The latter line is also the view of people like Rudolph Haag and Huzhiro Araki.

However as always I think one can only go so far with the founders and exegesis of their work (not that you are @bhobba as the thread is clearly about a historical question). They didn't clearly distinguish non-seperability from non-classical correlations, they didn't know about contextuality, decoherence, superselection, issues with the particle picture like the Unruh effect and so on.