time as – A physicist in the UK built a tiny “cosmos” from nearly 20,000 rubidium atoms chilled close to absolute zero. By letting two quantum sectors exchange particles, he created an internal notion of time inside the toy universe—an outcome that matches predictions f
In a lab where little seems to happen, time was the hardest thing to believe in.
Giovanni Barontini. at the University of Birmingham in the UK. says the question started in a place far from the instrumentation: watching his 6-year-old son play. The child was “building his own small universe. ” and Barontini found himself comparing that play to the ultracold-atom systems he builds in his own work—simple at first glance. and. to his mind. strangely quiet. If nothing changes, he wondered, it’s like time isn’t passing.
To test that intuition, Barontini turned to a quantum toy model of the cosmos. Using lasers and electromagnetic forces, he cooled around 20,000 rubidium atoms to temperatures close to absolute zero. He then split the atoms into two sectors—one labeled “bright” and the other “dark. ” a direct analogy to dark matter. In this initial setup, the toy universe was essentially timeless and unchanging.
The experiment changed when Barontini forced the two sectors to talk to each other. Lasers coaxed the “bright” and “dark” regions into exchanging atoms so they could interact at the quantum level. That interaction shifted the entropy—or disorder—of the universe.
In our own universe, time is understood to move in the direction of increasing entropy. Using that principle, Barontini could define an internal time inside the toy universe. With this internal time in hand. he then used the Schrödinger equation—one of quantum physics’ core tools for describing how systems evolve. The predictions for the atoms’ quantum states matched what the experiment produced.
The idea that time might not be fundamental, but could arise from quantum correlations instead, isn’t new. It traces back to physicist Nevill Mott in the 1930s, and it has been explored in theory ever since. The first experimental support for this kind of thinking came in 2013. when Marco Genovese at the National Metrology Institute of Italy and colleagues demonstrated feasibility using entangled particles of light—again. with a sense of time coming from quantum correlations.
Genovese says the new cold-atom work takes that concept further. In his view, it brings “significant progress,” particularly because the atomic “universe” is more complex than the light-based system. He also points to a key technical hurdle that Barontini cleared: making the Schrödinger equation work with the system’s internal time in this fuller. cold-atom setting. something that hadn’t been done before.
Outside the experiment. physicists are looking at it with mixed feelings—because the toy model sits right at the boundary of what quantum physics explains confidently and what still remains unresolved. Claus Kiefer at the University of Cologne in Germany connects the cold-atom result to the larger challenge of combining gravity and quantum theory into a single framework that could apply at all scales. That question remains open. Some physicists. Kiefer notes. suggest that such a theory would be marked by the absence of time at the most fundamental level. The toy universe experiment mimics that possibility. but Kiefer also cautions that it is not a perfect stand-in: as ultracold atoms move between sectors. they do not interact in the complex ways expected in a bigger universe.
Carlo Rovelli at Aix-Marseille University in France brings an even sharper criticism. Experiments of this kind. he says. can’t discover something fundamentally new about time because they are built on physics already understood. Still. Rovelli argues that using these setups as “mimics” of large unanswered problems could offer inspiration—especially for approaching unknown physics such as quantum gravity. the notoriously elusive issue that has resisted a clean resolution for decades.
For Barontini. the outcome is an experimental confirmation of ideas that have circulated for a long time—proof that they still hold up under laboratory pressure. But it doesn’t mean time works this way in the real universe at every scale. “It isn’t a confirmation that this is how time actually works at all scales,” he says.
Cosmologists, who study the entire universe rather than lab-made toy versions, are likely to raise objections. Barontini expects that, and he also has his next steps in mind. He wants to explore the ultracold “miniverse” further. including using lasers to create regions that atoms cannot move away from. resembling the pull of a black hole.
time as quantum illusion ultracold atoms rubidium atoms internal time Schrödinger equation entropy quantum correlations dark and bright sectors toy universe quantum gravity