Quantum Collapse Models Suggest Tiny Time Fluctuations

Quantum mechanics is rich with paradoxes and contradictions. It describes a microscopic world in which particles exist in a superposition of states—being in multiple places and configurations all at once, defined mathematically by what physicists call a "wavefunction." But this runs counter to our everyday experience of objects that are either here or there, never both at the same time. Typically, physicists manage this conflict by arguing that, when a quantum system comes into contact with a measuring device or an experimental observer, the system's wavefunction "collapses" into a single, definite state. Now, with support from the Foundational Questions Institute, FQxI, an international team of physicists has shown that a family of unconventional solutions to this measurement problem—called "quantum collapse models"—has far-reaching implications for the nature of time and for clock precision. They published their results suggesting a new way to distinguish these rival models from standard quantum theory, in Physical Review Research, in November 2025. "What we did was to take seriously the idea that collapse models may be linked to gravity," says Nicola Bortolotti, a Ph.D. student at the Enrico Fermi Museum and Research Center (CREF) in Rome, Italy, who led the study. "And then we asked a very concrete question: What does this imply for time itself?" Spontaneous collapse In the 1980s, physicists began exploring quantum models in which wavefunction collapse happens spontaneously, whether or not the system is measured or observed. Unlike what are commonly called 'interpretations' of quantum mechanics—which are primarily conceptual and experimentally indistinguishable from standard quantum theory—these quantum collapse models make predictions that are concrete and, in principle, testable. Bortolotti looked at two different models of quantum collapse, along with colleagues Catalina Curceanu, a member of FQxI and research director at the Laboratori Nazionali di Frascati of the National Institute for Nuclear Physics (INFN-LNF) in Frascati, Italy, Kristian Piscicchia, at CREF and INFN-LNF, Lajos Diósi, of the Wigner Research Center for Physics and Eötvös Loránd University, in Budapest, Hungary, and Simone Manti of INFN-LNF. One model, called the Diósi-Penrose model (named after FQxI members Lajos Diósi and Sir Roger Penrose), has long suggested that gravity is connected with wavefunction collapse. But for the first time, the new paper also drew a quantitative link between the second model, known as Continuous Spontaneous Localization, and gravitational spacetime fluctuations. The new paper shows that, if the collapse models are right, then time itself must exhibit a tiny intrinsic uncertainty, implying a fundamental, but extremely small, limit on clock precision. "Once you do the calculation, the answer is clear and surprisingly reassuring," said Bortolotti. There is no need to worry that this uncertainty will affect your wristwatch, though, or even the most precise atomic clocks in existence today or in the foreseeable future. "The uncertainty is many orders of magnitude below anything we can currently measure, so it has no practical consequences for everyday timekeeping," says Curceanu. "Our results explicitly show that modern timekeeping technologies are entirely unaffected," adds Piscicchia. Quantum gravity hints Physicists have long been questing after a unified theory that could unite quantum mechanics and gravity. Each theory is in exquisite accord with experimental results in its own domain: for quantum mechanics, the microscopic world of subatomic particles, and for gravity, as described by Einstein's general theory of relativity, the macroscopic realm of stars, galaxies and even the universe itself. Yet the two theories have dramatically different principles and approaches to time. "In standard quantum mechanics, time is treated as an external, classical parameter that is not affected by the quantum system being studied," explains Curceanu. In general relativity, however, time and space are malleable, shifting and warping under the influence of objects with mass. Building on work suggesting that quantum mechanics could be just one piece of a bigger and more fundamental theory of physics, the new paper hints at hidden connections between quantum mechanics, gravity, and time. Curceanu underlined the importance of FQxI's dedication to exploring unorthodox ideas. "There are not many foundations in the world which are supporting research on these types of fundamental questions about the universe, space, time, and matter," says Curceanu. "Our work shows that even radical ideas about quantum mechanics can be tested against precise physical measurements, and that, reassuringly, timekeeping remains one of the most stable pillars of modern physics."