Physicists Divided on What Quantum Mechanics Says about Reality | Scientific American
August 8, 2025<br>12 min read<br>Add Us On GoogleAdd SciAm<br>Physicists Can’t Agree on What Quantum Mechanics Says about Reality
A survey of more than 1,000 physicists finds deep disagreements in what quantum theories mean in the real world
By Elizabeth Gibney & Nature magazine<br>Olena Shmahalo/Nature
Quantum mechanics is one of the most successful theories in science — and makes much of modern life possible. Technologies ranging from computer chips to medical-imaging machines rely on the application of equations, first sketched out a century ago, that describe the behaviour of objects at the microscopic scale.<br>But researchers still disagree widely on how best to describe the physical reality that lies behind the mathematics, as a Nature survey reveals.<br>At an event to mark the 100th anniversary of quantum mechanics last month, lauded specialists in quantum physics argued politely — but firmly — about the issue. “There is no quantum world,” said physicist Anton Zeilinger, at the University of Vienna, outlining his view that quantum states exist only in his head and that they describe information, rather than reality. “I disagree,” replied Alain Aspect, a physicist at the University of Paris-Saclay, who shared the 2022 Nobel prize with Zeilinger for work on quantum phenomena.<br>On supporting science journalism<br>If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<br>To gain a snapshot of how the wider community interprets quantum physics in its centenary year, Nature carried out the largest ever survey on the subject. We e-mailed more than 15,000 researchers whose recent papers involved quantum mechanics, and also invited attendees of the centenary meeting, held on the German island of Heligoland, to take the survey.<br>The responses — numbering more than 1,100, mainly from physicists — showed how widely researchers vary in their understanding of the most fundamental features of quantum experiments.
Nature
As did Aspect and Zeilinger, respondents differed radically on whether the wavefunction — the mathematical description of an object’s quantum state — represents something real (36%) or is simply a useful tool (47%) or something that describes subjective beliefs about experimental outcomes (8%). This suggests that there is a significant divide between researchers who hold ‘realist’ views, which project equations onto the real world, and those with ‘epistemic’ ones, which say that quantum physics is concerned only with information.
Nature
The community was also split on whether there is a boundary between the quantum and classical worlds (45% of respondents said yes, 45% no and 10% were not sure). Some baulked at the set-up of our questions, and more than 100 respondents gave their own interpretations (the survey, methodology and an anonymized version of the full data are available online).
Nature
“I find it remarkable that people who are very knowledgeable about quantum theory can be convinced of completely opposite views,” says Gemma De les Coves, a theoretical physicist at the Pompeu Fabra University in Barcelona, Spain.<br>Nature asked researchers what they thought was the best interpretation of quantum phenomena and interactions — that is, their favourite of the various attempts scientists have made to relate the mathematics of the theory to the real world. The largest chunk of responses, 36%, favoured the Copenhagen interpretation — a practical and often-taught approach. But the survey also showed that several, more radical, viewpoints have a healthy following.<br>Asked about their confidence in their answer, only 24% of respondents thought their favoured interpretation was correct; others considered it merely adequate or a useful tool in some circumstances. What’s more, some scientists who seemed to be in the same camp didn’t give the same answers to follow-up questions, suggesting inconsistent or disparate understandings of the interpretation they chose.<br>“That was a big surprise to me,” says Renato Renner, a theoretical physicist at the Swiss Federal Institute of Technology (ETH) in Zurich. The implication is that many quantum researchers simply use quantum theory without engaging deeply with what it means — the ‘shut up and calculate’ approach, he says, using a phrase coined by US physicist David Mermin. But Renner, who works on the foundations of quantum mechanics, is quick to stress that there is nothing wrong with just doing calculations. “We wouldn’t have a quantum computer if everyone was like me,” he says.<br>Copenhagen still reigns supreme<br>Over the past century, researchers have proposed many ways to interpret the...