What physicists believe about quantum mechanics
A few years ago David Bourget and David Chalmers did a follow up survey to the 2009 one polling philosophers on what they believe about various questions. One of them was quantum mechanics, particularly the measurement problem and its various interpretations. Over the decades there have been surveys of physicists themselves on this question, but most, if not all, were with a very small sample size, usually only the attendees at a particular conference.
As part of the Quantum Centennial (the celebration of 100 years of quantum mechanics) Nature has done a fairly large survey of the community of quantum researchers with over 1100 respondents. The results are interesting, although not particularly surprising.
Copenhagen still comes out on top with 36%. It’s interesting that it’s stronger with experimentalists than with theorists (half vs a third). I suspect the experimentalists are hewing to a very pragmatic version of the interpretation. Which highlights a concern that the term “Copenhagen interpretation” means different things to different people. The article acknowledges this, noting that 29% of those who selected Copenhagen favored an ontic version of the wave function vs 63% who came down epistemic.
15% are Everettians (or “consistent-history” advocates, who I suspect object to being lumped in with the many-worlders), 7% Pilot-wave, 4% Spontaneous collapse, 4% Relational Quantum Mechanics, and a smattering in other views.
Overall 47% of respondents see the wave function as just a mathematical tool, with 36% taking a partial or complete realist take (my view), and 8% taking it to only represent subjective beliefs about experimental outcomes.
45% see a boundary between classical and quantum objects (5% see it as sharp) while 45% don’t (my view).
Just before the paywall, there is a question about the observer in quantum mechanics, with 9% saying it must be conscious. Another 56% said there had to be an observer, but that “observer” can just be interaction with a macroscopic environment, and 28% arguing that no observer at all is needed. (I think interaction with the macroscopic environment and the resulting decoherence is key, but it seems misleading to call that environment an “observer”.)
All interesting. Of course, how popular or unpopular a view is has no real bearing on whether it’s reality. Prior to Galileo’s telescopic observations in 1609, an Earth-centered universe was the most popular cosmology. Only a miniscule handful of astronomers accepted Copernicus’ view about the Earth orbiting the sun. Until the quantum-measurement equivalent of the telescope comes along, all we can do is reason as best as possible with the current data.
The results here are interesting to compare with what the philosophers thought on the Bourget-Chalmers survey. On quantum mechanics, philosophers were 24% agnostic, 22% hidden variable theories, 19% many-worlds, 17% collapse, and 13% epistemic. Once we take into account all the various forms of “Copenhagen interpretation”, these seem in a similar ballpark, except that philosophers are more open to hidden variable approaches. (It may be easier to favor hidden variables if you’re not the one who has to find them.)
My own view comes down to a preference for structural completeness (or at least more structurally complete models), which to me currently favors a cautious and minimalist take on the Everettian approach (as I described a few months ago). However, my credence in this conclusion is only 75-80%. That the survey indicates most physicists aren’t super confident in their own conclusions here makes me feel better.
This reminds me of a new approach that Jacob Barandes has been promoting on various podcasts (see this recent Sean Carroll episode as an example). Barandes calls it Indivisible Stochastic Quantum Mechanics. I won’t pretend to understand exactly what he’s trying to accomplish with it, but it involves rejecting the wave function completely, and replacing it with something more stochastic from the beginning. Which strikes me as less structurally complete than the wave function, and so a move in the wrong direction. But maybe I’ll turn out to be wrong.
Anyway, now we have a firmer idea of where the physics community currently stands on quantum interpretations, or at least a firmer one than we did before. How would you have answered the survey questions? (There’s actually a small quiz in the article which is worth taking to see the logic leading to particular interpretations.)
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