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Physicists have created a tiny laboratory “universe” in which time appears to emerge naturally from the behavior of a quantum system, a breakthrough that could help answer one of the deepest questions in modern physics: What is time?
The experiment, led by Professor Giovanni Barontini at the University of Birmingham, demonstrates that the passage of time can be measured without relying on an external clock. Instead, researchers found that a version of time arose from changes occurring within the quantum system itself, offering the first controlled experimental evidence supporting a concept long explored in theories of quantum gravity. The findings were published in Physical Review Research.
Some leading theories, including those based on the Wheeler-DeWitt equation, suggest that time may not be a fundamental feature of the universe. Instead, the familiar flow of time could emerge from interactions between different parts of a quantum system rather than from an independent, ever-ticking clock.
To investigate this idea, Barontini’s team created a simplified quantum “universe” containing 24,000 ultracold atoms cooled to just a few billionths of a degree above absolute zero. The atoms were confined inside an isolated system divided into two regions by laser beams. Within the observed region, the cloud repeatedly expanded and contracted, resembling a simplified version of a Big Bang followed by a hypothetical Big Crunch.
Because the system remained isolated, researchers reconstructed the sequence of events using only information generated inside the miniature universe, without referring to any external timekeeping device. They found that time emerged from changes in entropy, or the distribution of particles between the two regions. As long as that distribution continued to change, time effectively moved forward. When the changes stopped, time also came to a halt.
The researchers call this concept “entropic time.” In the experiment, it consistently moved in one direction, correctly ordered events, and even sped up or slowed down depending on how entropy changed.
The study also showed that the Schrödinger equation, the foundation of quantum mechanics, can be expressed using entropic time. The team believes the approach could provide a powerful new platform for testing ideas about quantum gravity, the early universe, black holes, and the origins of time itself under controlled laboratory conditions.
