Quantum mechanics has always challenged our everyday understanding of reality. In the quantum world, particles can exist in a superposition of states, meaning they can occupy multiple possible positions or configurations at the same time. Physicists describe these possibilities mathematically using a wavefunction.
That picture is very different from ordinary life, where an object appears to be in one place and one state at a time. To bridge that gap, standard quantum mechanics says that when a quantum system is measured or observed, its wavefunction collapses into a single definite outcome.
Now, with support from the Foundational Questions Institute, FQxI, an international team of physicists has explored a more radical possibility. Their work suggests that certain alternatives to standard quantum mechanics, known as quantum collapse models, could have surprising consequences for the nature of time itself and for the ultimate precision of clocks.
The findings, published in Physical Review Research, also point to a possible new way to test these unconventional theories against standard quantum mechanics.
“What we did was to take seriously the idea that collapse models may be linked to gravity,” says Nicola Bortolotti, a PhD student at the Enrico Fermi Museum and Research Centre (CREF) in Rome, Italy, who led the study. “And then we asked a very concrete question: What does this imply for time itself?”
When Quantum States Collapse on Their Own
Beginning in the 1980s, physicists developed models in which wavefunction collapse does not require a measuring device or an observer. Instead, collapse can happen spontaneously.
That makes these ideas different from many interpretations of quantum mechanics. Interpretations mainly offer different conceptual explanations for what quantum theory means, while typically producing the same experimental predictions as standard quantum mechanics. Quantum collapse models go further because they predict physical effects that could, at least in principle, be measured.
Bortolotti and his colleagues examined two different collapse models. The team included 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 of the models was the Diósi-Penrose model (named after FQxI members Lajos Diósi and Sir Roger Penrose). It has long proposed that gravity may play a role in forcing quantum systems to collapse into definite states.
The researchers also studied a second approach called Continuous Spontaneous Localization. For the first time, they established a quantitative connection between that model and gravitational fluctuations in spacetime.
Time May Have a Tiny Built-In Uncertainty
The calculations led to a striking conclusion. If these collapse models are correct, then time itself should contain a very small amount of intrinsic uncertainty.
In other words, there may be a fundamental limit to how precisely time can ever be measured. That does not mean clocks suddenly become unreliable. The predicted effect is extraordinarily small.
“Once you do the calculation, the answer is clear and surprisingly reassuring,” said Bortolotti.
Even the most advanced atomic clocks operating today, or those expected in the foreseeable future, would not be precise enough to notice the effect.
“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.
A Possible Clue to Quantum Gravity
The work touches on one of the biggest unsolved problems in modern physics: how to reconcile quantum mechanics with gravity.
Quantum mechanics has been enormously successful at describing atoms, particles, and other microscopic systems. Einstein’s general theory of relativity, meanwhile, describes gravity and the behavior of space and time on much larger scales, including planets, stars, galaxies and even the universe itself.
Both theories agree extremely well with experiments in the domains where they are used. The problem is that they treat time in fundamentally different ways.
“In standard quantum mechanics, time is treated as an external, classical parameter that is not affected by the quantum system being studied,” explains Curceanu.
General relativity takes a very different view. Space and time are part of a flexible structure called spacetime, which can bend and change in response to mass and energy.
Because of this mismatch, physicists have spent decades searching for a deeper theory that could unite quantum mechanics and gravity. The new results suggest that collapse models may contain clues about how quantum physics, gravity, and time could ultimately fit together.
They also offer a more practical benefit. Since collapse models predict measurable effects that differ from standard quantum mechanics, extremely precise experiments could eventually help determine whether these ideas describe something real in nature.
Curceanu emphasized the importance of supporting research into unconventional questions at the foundations of physics.
“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.”
This work was partially supported through FQxI’s Consciousness in the Physical World program.