In July 1925—exactly a century ago—famed physicist Werner Heisenberg wrote a letter to his equally famous colleague, Wolfgang Pauli. In it, Heisenberg confesses that his “views on mechanics have become more radical with each passing day,” requesting Pauli’s prompt feedback on an attached manuscript he’s considering whether to “complete…or to burn.”
That was the Umdeutung (reinterpretation) paper, which set the foundation for a more empirically verifiable version of quantum mechanics. For that reason, scientists consider Umdeutung’s publication date as quantum mechanics’s official birthday. To commemorate this 100th anniversary, Nature asked 1,101 physicists for their take on the field’s most fiercely debated questions, revealing that, as in the past, the field of quantum physics remains a hot mess.
Published today, the survey shows that physicists rarely converge on their interpretations of quantum mechanics and are often unsure about their answers. They tend to see eye-to-eye on two points: that a more intuitive, physical interpretation of math in quantum mechanics is valuable (86%), and that, perhaps ironically, quantum theory itself will eventually be replaced by a more complete theory (75%). A total of 15,582 physicists were contacted, of which 1,101 responded, giving the survey a 7% response rate. Of the 1,101, more than 100 respondents sent additional written answers with their takes on the survey’s questions.
‘Textbook’ approach still tops, with a caveat
Participants were asked to name their favored interpretation of the measurement problem, a long-standing conundrum in quantum theory regarding the uncertainty of quantum states in superposition. No clear majority emerged from the options given. The frontrunner, with 36%, was the Copenhagen interpretation, in which (very simply) quantum worlds are distinct from classical ones, and particles in quantum states only gain properties when they’re measured by an observer in the classical realm.
It’s worth noting that detractors of the Copenhagen interpretation scathingly refer to it as the “shut up and calculate” approach. That’s because it often glosses over weedy details for more practical pursuits, which, to be fair, is really powerful for things like quantum computing. However, more than half of physicists who chose the Copenhagen interpretation admitted they weren’t too confident in their answers, evading follow-up questions asking them to elaborate.
Still, more than half of the respondents, 64%, demonstrated a “healthy following” of several other, more radical viewpoints. These included information-based approaches (17%), many worlds (15%), and the Bohm-de Broglie pilot wave theory (7%). Meanwhile, 16% of respondents submitted written answers that either rejected all options, claimed we don’t need any interpretations, or offered their personal takes on the best interpretation of quantum mechanics.
So, much like many other endeavors in quantum mechanics, we’ll just have to see what sticks (or more likely, what doesn’t).
Divided results, equivocal reviews
Physicists who discussed the results with Nature had mixed feelings about whether the lack of consensus is concerning. Elise Crull at the City University of New York, for instance, told Nature that the ambiguity suggests “people are taking the question of interpretations seriously.”
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