Researchers at the University of Birmingham have conducted an experiment suggesting that time may not be a fundamental feature of the universe but rather something that emerges from changes within physical systems. Using approximately 24,000 atoms cooled to near absolute zero, Professor Giovanni Barontini created a controlled quantum environment to test this concept, with findings published in Physical Review Research.
The experiment was motivated by theoretical physics frameworks, such as the Wheeler-DeWitt equation used in quantum gravity research, which describe the universe without an external time variable. This creates a fundamental puzzle: if no external clock exists, how do events occur in any particular order? One potential answer is that time arises from the changing relationships and distributions within the universe itself.
Barontini’s miniature system divided atoms into two regions using laser beams at different frequencies. The bright region underwent cycles resembling expansion and contraction, analogous to cosmological events like the Big Bang and Big Crunch. Crucially, the experiment measured time not through conventional seconds or minutes, but through changes in how atoms were distributed within the system—a concept Barontini termed “entropic time.”
The results demonstrated that this internally-derived measure of time possesses several key properties. It consistently moves in one direction, establishing what physicists call the arrow of time that distinguishes past from future. Entropy-based time also correctly sequences events even as the system expands and contracts, and notably, it does not advance at a constant rate but varies depending on entropy changes within the system.
The findings provide experimental evidence that time can be operationally defined by changes within a system rather than relying on an external reference. The research also showed that the Schrödinger equation, fundamental to quantum mechanics, can be expressed using entropic time. These results offer new perspective on a central puzzle in physics: why everyday experience shows a clear direction of time when fundamental physical laws typically work equally well forward and backward.
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