Is David Deutsch correct in stating that the Copenhagen interpretation of QM has few defenders left? [closed]

Question

In his site here, he says

Confusion, obfuscation or inconsistency, including non-dynamical ‘wave function collapse’ theories, the ‘Copenhagen interpretation’ (which is in some sense still the canonical view of quantum theory, though it has few actual defenders left), and much of the informal discussion of the meaning of quantum theory that appears in textbooks. To these we must add countless concoctions of pseudo-science and mysticism to which this whole regrettable and unnecessary controversy has inevitably opened the door.

He also makes the more bold claim that any instrumentalist interpretations of QM are not really interpretations but rather a way to simply ignore what the evidence of QM tells them about reality,

In addition to these disputes over rival conceptions of reality, there have sometimes been disputes between a realistic theory and an instrumentalist doctrine that denies that the theory describes reality. For example the Inquisition in Galileo’s time permitted advocacy of the heliocentric theory if it was regarded purely as a means of predicting astronomical observations, but not if it was interpreted as a factual theory of where and what the planets and the Earth are. Similar instrumentalist doctrines have been applied to quantum theory. What these miscellaneous revisionist views of scientific theories have in common is a loss of philosophical nerve in situations where, as Lockwood puts it, “there are no conservative options”. That is, they are not so much bona fide rival ontologies struggling to be heard, as psychological manoeuvres whose purpose is to blind their defenders to evidence of something unwelcome: the motion of the Earth, the curvature of spacetime, dinosaurs, or other universes.

From the general gist of the article, he seems to be stating that the Copenhagen interpretation is vague and/or inconsistent and doesn’t really tell us much. However, from a poll that was conducted among physicists (although admittedly more than a decade ago), it seems that the interpretation still is shared by the most number of physicists (although still less than 50%).

Is this because it is still the most accepted interpretation or because it is often used as a euphemism for “we don’t really know or care about what’s going on underneath” in physics?

It seems that Sean Carroll expounds a similar view after discussing that poll in his blog,

I’ll go out on a limb to suggest that the results of this poll should be very embarrassing to physicists. Not, I hasten to add, because Copenhagen came in first, although that’s also a perspective I might want to defend (I think Copenhagen is completely ill-defined, and shouldn’t be the favorite anything of any thoughtful person). The embarrassing thing is that we don’t have agreement.

Answer 1

The 2011 survey, which was of just 33 physicists, showed Deutch was asserting a falsehood. The 2016 survey, with a larger survey population of 149 participants, likewise showed a plurality for Copenhagen. https://www.newscientist.com/article/mg23331074-600-physicists-cant-agree-on-what-the-quantum-world-looks-like/#:~:text=There%20was%20no%20consensus%20among,had%20no%20preference%20at%20all.

The more recent and larger survey shows Copenhagen is even more dominant than the 2011 one, as all other options combined only gathered 25% support, vs, the 39% for Copenhagen.

A peculiarity of the 2011 survey, along with its very small sample size is that its percentages sum to significantly more than 100% for the supposedly single preferred interpretation for the survey takers! These two observations make me at least somewhat suspicious of its results.

Here are the results of the 2016 survey:

https://arxiv.org/pdf/1612.00676.pdf

Answer 2

Upon what evidence would you expect an answer to be based? Who would qualify as a bona fide 'defender'? Would you confine the role of the defence of Copenhagen to physicists specialising in quantum theory and its applications? Would you want to canvass all of them, or would you accept another poll? How would you ensure the poll was representative and not overly populated with the views of people such as DD?

I think that where DD is right is in saying that the Copenhagen description is full of unsatisfactory conceptual holes. Where he is wrong, in my opinion, is that he is biased towards a particular way of looking at the meaning of QM.

I doubt you will find 'defenders' of Copenhagen in the sense of there being people who will fanatically promote it in the same way as some people promote competing interpretations. What you will find are many practicing physicists who are comfortable with Copenhagen, because it was the basis upon which they learned QM, who understand its conceptual limitations, but are skeptical about paying too much attention to a mutually inconsistent array of competing ideas based on metaphysical speculations which don't make a difference to their calculations anyway.

If a rival interpretation emerges which allows calculations that are simpler or in better agreement with experiment, I'm sure Copenhagen will get binned in favour of it. However, nonsense such as 'I am drinking tea and simultaneously drinking coffee' is not going to be the basis upon which serious physicists will flock to another interpretation.

Answer 3

I can, as a lay person interested in qm, try to explain some of David Deutsch words, hopefully successfully:

First of all, Copenhagen is taught by default at universities - they teach it as if it's the standard or most obvious interpretation - which means that most physicists who aren't interested in investigating the question of interpretation are possibly naturally predisposed to answer "Copenhagen" by default. If you don't ever bother to think about the question, you'll just say what your teachers and your textbook say.

Secondly, the Copenhagen interpretation is also sometimes called "shut up and calculate" - shut up and calculate is not an interpretation, it's an anti interpretation. It's saying "we don't need to interpret what's happening, we just need to use the models to make useful predictions". That's fine as an opinion, but it's not an interpretation, it doesn't give us an idea of what's really going on with quantum experiments, which is exactly what quantum interpretations are supposed to do - they're supposed to tell us what's really going on. Not all Copenhagen interpretationsists will say that it's just shut up and calculate, some of them will say it's a real interpretation with real consequences for how the world works and why quantum mechanics gives good predictions.

David Deutsch is a physicist and he speaks to a lot of physicists, which means that he may have a deeper understanding of the views of his fellow physicists than can be accurately gathered in a poll. He may, in his experience talking to thousands of other physicists, have learned that one of the above two explanations - or both to some degree - explain why most physicists write down "Copenhagen" when asked for their preferred interpretation. Most of them may choose that because they simply prefer not to think about interpretations at all. It's also possible that he's just wrong, and you should take the poll results at face value.

I don't know if he's correct or not, I haven't spoken with thousands of physicists. Copenhagen seems like a particularly bad choice to me, because it conflicts with Relativity, but what do I know?

Answer 4

I learn from the answer of @Dcleve that Deutsch is not correct with his estimate about the degree of acceptance of the Copenhagen interpretation of Quantum Mechanics (QM).

But the percentage of supporters of one or the other interpretation is not the most interesting aspect of this problem of the century. Much more important is to understand where and how the many interpretations differ from each other. And on which formal mathematical basis they rely.

Because the present site is a philosophical and not a physics platform, it may be helpful to recall the key idea and the mathematical basis of each interpretation. A former post on this site recommended the following paper Nine formulations of quantum mechanics.

The paper gives an ecellent overview over these nine formulations of QM and the mathematical key concepts of each. It also indicates further references. The paper has a pedagogical aim, and addresses non-specialists.

Note. I changed the term "interpretation" to "formulation" in my last section due to the current comments. Confer also the corresponding remark on p. 288 of the linked paper.

Answer 5

Carlo Rovelli has an update of the Copenhagen Interpretation that plugs some of its gaps called Relational QM. This supposes that it is not just a classical measuring apparatus which is an observer, but essentially any interaction between quantum systems. This has its defenders.