EDITORIAL30 July 2025Nature survey shows that disagreement about the meaning of quantum physics remains strong, even 100 years in. And that’s OK.Scientists met in June on the island of Heligoland in Germany to celebrate 100 years of quantum mechanics.Credit: ShutterstockAsk a bunch of physicists to explain a quantum experiment and you’re unlikely to get the same description twice. Everyone agrees that the mathematical framework of quantum mechanics is peerless at predicting the results of experiments exploring the subatomic world. Moreover, it can be used to build technology ranging from computer chips to lasers and nuclear clocks. But what the theory means physically remains a mystery — and, so far, a matter of mainly subjective interpretation.Some scientists are embarrassed, 100 years after quantum theory was first formulated, by this inability to agree on a single narrative about the basic nature of reality, and the particles and forces that shape it. They shouldn’t be. Physicists should revel in the diversity of thought that the field represents and seize on philosophical disagreements as a way to spur further discoveries.Physicists disagree wildly on what quantum mechanics says about reality, Nature survey showsQuantum mechanics lets researchers agree with extreme precision on the expected outcomes of observations. That’s odd, given that experiments seem to show that the quantum world is itself probabilistic and uncertain. Objects seem to behave like waves, interfering with each other and themselves, until they are measured, at which point they adopt more-definite, particle-like behaviours. The phenomenon of entanglement can bind the fate of particles together, even if they are separated physically over long distances, and this effect can be used to send secret signals. Statistical rules seem to govern the outcome of experiments.The disagreements start when you ask physicists what precisely is meant by many of the words above. Not only does language mean radically different things to different people, but there are several ways to interpret what, if anything, lies behind phenomena such as randomness and what happens to quantum objects between measurements.The degree of disagreement is reinforced in a News Feature this week. Nature’s news team conducted the largest-ever survey asking quantum physicists about the foundations of their discipline. The responses reveal that there is little or no consensus on questions about whether a particle really can exist in two places at once, whether there are multiple universes or whether it is sensible to think of the mathematical quantities underpinning quantum mechanics as corresponding to something real. A basic tension among those studying the foundations of quantum theory is between ‘realists’, who think quantum physics can and should describe a visualizable account of the world, and those who embrace an ‘epistemic’ view that interprets the theory as being exclusively about knowledge and predicting experimental outcomes.Such disagreement might make it harder to communicate quantum physics to the public, and to avoid ambiguity that can be seized on by pedlars of pseudoscience. But these discussions make the field all the more fascinating — and propel science forwards. Research in what physicists call quantum foundations has not only helped scientists to probe the limits of quantum mechanics but also fed the development of technologies such as quantum computers and quantum cryptography. Such work might ultimately point the way to an improved theory that incorporates gravity — the only fundamental force of nature for which quantum theory currently can’t account — and shed light on other outstanding mysteries in physics.Hundreds of physicists on a remote island: we visit the ultimate quantum partyIn Nature’s survey, some 75% of researchers thought that quantum theory will be superseded, at least in part, by a more complete theory. For experimentalists such as Alain Aspect, a physicist at the University of Paris-Saclay who won the 2022 physics Nobel prize for exploring quantum phenomena, studying quantum foundations is a way to advance the field. “Thinking about foundations allows us, allows me, at least, to develop images, and these images are good for my intuition,” Aspect said in June at a conference on the German island of Heligoland, where scientists had convened to celebrate 100 years of quantum mechanics. Such discussions were at the forefront of the conference.Physicists are making progress in understanding the foundations of quantum physics. Thought experiments, such as those by Renato Renner and Daniela Frauchiger, theoretical physicists at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland, have placed limits on what various interpretations can simultaneously suggest is true (D. Frauchiger and R. Renner Nature Commun. 9, 3711; 2018). And dark-matter experiments using the XENONnT experiment have ruled out some of the proposed interpretations that would require modifying the Schrödinger equation, which governs the evolution of quantum states in time (E. Aprile et al. Preprint at arXiv https://doi.org/pxg2; 2025). But how best to create a less fuzzy image of the quantum world? One way would be to deepen the dialogue between physicists and philosophers, suggests Alyssa Ney, a philosopher of physics at Ludwig Maximilian University of Munich in Germany. That would improve understanding of the differing language and assumptions of quantum interpretations.Why even physicists still don’t understand quantum theory 100 years onOne of the most widespread approaches to understanding quantum theory, known as the Copenhagen interpretation, started in an amalgamation of the views of two of the field’s founders, Niels Bohr and Werner Heisenberg, who didn’t always agree. Their approach — which assumes that it is not the job of a theory to concern itself with what is not observable — works well for experimentalists. But Nature’s survey suggests that it finds less favour with those studying the philosophical underpinnings of quantum theory. And few physicists are taught that other theories — even seemingly radical ones, such as the many-worlds interpretation, which proposes that vast numbers of universes exist — can also account for observations. “When you learn quantum physics, somehow you’re never confronted with even the idea that there are different interpretations,” says Renner.The curiosity to learn about and explore other interpretations can help scientists to push physics forwards. Physics and philosophy are now less intertwined than they have ever been, but they need each other. Teachers of undergraduate physics should embrace philosophical questions, not just practical ones. Gnarly, if amiable, discussions about the meaning of words and physics concepts, of the kind that thrived at the Heligoland conference, should be encouraged.A century from now, quantum physicists might still not agree. But staying curious about what it all really means will deliver gains beyond consensus.