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First, I read the questions FAQ for this and I hope this does not violate the rules. I am not asking for personal opinion, but for observations of hard evidence of trends on this subject.

When I studied QM, as a senior in my physics curriculum, the Copenhagen Interpretation was the orthodoxy. It did what most scientists needed: consistently correlated very well with measurements. Of course, it was not perfect as an end-to-end description of what happens; for example, there was the so-called measurement problem. However, I imagine that it retained popularity, at least partly, because anything that was more end-to-end oriented, for instance addressing or side-stepping wave function collapse, was more complicated and didn't predict anything new that could be confirmed.

However, many years have passed. Other interpretations have emerged, such as Consistent Histories combined with Decoherence. Some are certainly very insightful and have a lot of value in their own right.

I am wondering if you are seeing any of those alternatives to Copenhagen really gaining traction/popularity, among physicists, above all the others, and a trend toward a real shift away from Copenhagen as the standard orthodoxy that is passed down in senior and first-year grad texts to new students?

If this question is too fluffy, I will gladly withdraw it, or feel free to close it. Again, I am asking for objective observations of a trend away from Copenhagen, toward some specific alternative, not your personal opinion of which interpretation is "best".

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    $\begingroup$ Comments are not for extended discussion (which I sense coming on); this conversation has been moved to chat. $\endgroup$
    – David Z
    Commented Feb 11, 2016 at 4:43
  • $\begingroup$ By "Copenhagen interpretation" do you mean the idea that the wave function represents a single objective reality and that it collapses when human beings measure the system? Some subset of that sentence? Help me out here. $\endgroup$
    – DanielSank
    Commented Feb 11, 2016 at 7:31
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    $\begingroup$ @DanielSank: Is that what they are teaching as Copenhagen interpretation these days? Really? $\endgroup$
    – CuriousOne
    Commented Feb 11, 2016 at 7:35
  • $\begingroup$ @CuriousOne I asked the question in an attempt to understand what OP has in mind. I never got anything resembling a definition of "Copenhagen interpretation" when I was in school. My suggested definition in the previous comment is what I think it means based on what folks seem to have in mind when they use that phrase. Again, I asked because I don't know. $\endgroup$
    – DanielSank
    Commented Feb 11, 2016 at 7:42
  • $\begingroup$ Wikipedia: "According to the interpretation, the interaction of an observer or apparatus that is external to the quantum system is the cause of wave function collapse, thus according to Paul Davies, "reality is in the observations, not in the electron"". The biggest differentiator is probably the unique role of the observer, compared to most other interpretations. Another hallmark is the proposal of wave function collapse with measurement, but no mechanism for wave function collapse. Also, it separates the classical (apparatus) from the quantum realm, but with no clear dividing line. $\endgroup$
    – David
    Commented Feb 11, 2016 at 15:23

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A 2013 poll involving 33 specialists at a quantum foundations meeting gave 42% for Copenhagen, 28% for information-based interpretations, 18% for Everett.

Only 15% of the specialists thought that the measurement problem is solved by decoherence.

Link: arxiv.org/abs/1301.1069

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I would say there is more freedom in thinking about the meaning of concepts in quantum theory now than it was in the cold war era. New interpretations were proposed and are discussed and new papers are published on this subject.

If we asked all physicists, including experimenters, which interpretation they prefer I would say most would not even know what the different interpretations are about, but I think most would prefer to stick with the minimal, shortest, least pretentious approach one can infer from the university courses - it is a mathematical scheme that has been successful predicting probabilities of results of many experiments, discovering new laws etc. but with no implication on the reality of $\psi$ function, operators or anything. I think this is quite close to Copenhagen, so when pressed, those people would probably vote for Copenhagen.

If we asked people who study this for a living, I think greater percentage of votes would go to newfangled interpretations, like the Bohm - de Broglie and the fundamentalist interpretation (Universe=big $\psi$) and others. There were some polls but they were quite limited in the number of participants and had differing results, so the most popular one among experts is not known.

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The measurement problem was more or less solved in the 1970s/80s by von Neumann's theory of measurement, the density matrix and decoherence, which explain the Born rule, which is the one thing that is actually perplexing about the Copenhagen interpretation. The basic principles behind measurement and decoherence had been understood intuitively since 1929 when Mott published a paper explaining alpha particle tracks using wave mechanics, so what remained left to do was to establish a theoretical framework for these sporadic calculations that had been done almost in parallel with the formulation of quantum mechanics.

In this sense there is no need for non-trivial changes to the Copenhagen interpretation (or for new interpretations in general) as the "problems" that came with it have fairly natural and straight forward solutions within the same framework in which Copenhagen is useful.

I would also point out that physics proper hasn't cared about the foundations of QM since the 1930s. It has long (since the mid 1930s) moved on to quantum field theory and I would suggest you do, too. QFT offers a more self-consistent picture of the world than non-relativistic quantum mechanics can, and that removes a lot of the "burning" questions that seem to be part of the Copenhagen interpretation for many who are new to QM.

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    $\begingroup$ I have never seen anything that explains the Born rule. Without more explanation here I think the statement that Von Neumann's theory explains it is incorrect. Second, I disagree that Copenhagen has no material problems; see Wigner's friend. Finally, the statement that "physics proper" (whatever that means, and I doubt it means anything well defined) is incorrect. People still do improved versions of Bell violation experiments and publish them in physics journals. By what other metric can we possibly define "physics proper"? $\endgroup$
    – DanielSank
    Commented Feb 11, 2016 at 7:46
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    $\begingroup$ @DanielSank: The density matrix formalism explains the Born rule. You are welcome to write an answer why you think it doesn't. Any extension of Schroedinger's cat that doesn't fix its shortcomings (and there are nothing else in it than shortcomings as far as I am concerned) isn't even worth considering. In any case, those things are all poor philosophy, they aren't physics. Physics proper is the science that finds explanations for new observations. Having said that, I am not saying that there isn't interesting stuff there... interpretations are just not the right stuff. $\endgroup$
    – CuriousOne
    Commented Feb 11, 2016 at 7:52
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    $\begingroup$ @DanielSank: Bell is not physics, it's philosophy posing for natural science. $\endgroup$
    – CuriousOne
    Commented Feb 11, 2016 at 7:53
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    $\begingroup$ "I would also point out that physics proper hasn't cared about the foundations of QM since the 1930s"? Well, given the 1-2 foundational papers that are put on the arXiv almost every day, that really seems to be a debatable statement. Whether me or you or whoever else consider these works as "nothing but philosophy" does not change the fact that there are still lots of people actively working on foundational issues. QFT is another matter entirely, and a lot of work on QM has nothing to do with QFT (see e.g. the whole of quantum information) $\endgroup$
    – glS
    Commented Mar 7, 2016 at 22:02
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    $\begingroup$ And that is just another opinion added to the mix. As I said, I may or may not agree with you in this, but to say that the physics community has moved along and does not care anymore about the foundations of QM is simply not backed up by the reality. No, the fact that something is published on the arxiv certainly does not make it true or worthy of read, but neither you can speak on behalf of the whole community saying that it is a fact that "nothing new ever emerges". I think you are confusing what you wish people were doing with what is actually actively studied. $\endgroup$
    – glS
    Commented Mar 7, 2016 at 22:29

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