Representative Image A scientist at the University of Birmingham has built a mini universe out of about 24,000 atoms to show that time can be measured without a clock. Giovanni Barontini's experiment tracks the order of events purely through changes in entropy, the measure of disorder in a system.The result matters because physics still has no settled answer on what time is. General relativity and quantum mechanics describe it differently, and this lab-made universe offers a controlled way to study that mismatch.The atoms are rubidium, chilled to almost absolute zero, which is around minus 273 degrees Celsius. At that temperature they stop behaving like separate particles and act more like a single cloud. US Midterm Election Results 2026 The cloud sits in a trap it cannot escape. A specially configured laser splits the trap into two halves. One is the bright side, which was observed. The other is the dark side, which stays unobserved. Entropy, not a clock, keeps time in this mini universe Only the bright side served as the timekeeper. Its entropy kept changing, and the internal timer moved forward only when atoms crossed the laser barrier between the two halves. By watching the cloud expand and contract, and by tracking the exchange of atoms, it became possible to work out the order in which events happened. There was a catch. When no atoms crossed over, the internal clock stopped. An external clock kept running anyway, so the two disagreed on when events took place. Inside this system, time did not match the time outside it.The experiment could help link relativity and quantum physicsBoth theories underpin modern physics, yet they do not always agree on how time works. In certain quantum systems, for instance, time can be reversed. Showing that time can be read from entropy changes in an atomic system is a step toward bringing the two together.Barontini's model is only a starting point. It leaves out factors such as black holes, and several settings can be changed, including the shape of the trap, the density of the atoms and the height of the laser barrier.The cloud's repeated swings between the dark and bright sides could also help scientists simulate conditions just after the Big Bang. It might even help model the lead-up to the Big Crunch, the theoretical point at which the universe collapses into itself.The full impact will take a while to show. For now, it answers a simple question: you do not need a clock to tell time, as long as something keeps changing.