Professor Giovanni Barontini at the University of Birmingham created a miniature quantum system containing approximately 24,000 atoms cooled to a few billionths of a degree above absolute zero. He demonstrated that a measure of time can emerge from changes within the system itself, without relying on an external clock.
Two laser beams at different frequencies divided the system into an observed region and an unobserved region. The observed region underwent cycles of expansion and contraction resembling simplified versions of a Big Bang and Big Crunch. As atoms moved between regions, their distribution changed, providing what Barontini called "entropic time" - a way to track the system's progression based on entropy rather than conventional timekeeping.
This entropic time moved consistently in one direction, establishing an "arrow of time" that placed events in the correct sequence. It also advanced at varying rates depending on how entropy changed within the system. Barontini showed that the Schrödinger equation, a foundational equation of quantum mechanics, can be expressed using this internally generated measure of time.
The findings, published in Physical Review Research, provide experimental evidence for a theoretical idea that time may not be fundamental to the universe but could arise from relationships and changes within it. This connects to questions in quantum gravity about how the universe behaves when quantum effects and gravity must be considered together.
Barontini stated: "This study provides the first controlled experimental evidence that 'time' can be defined by changes within a system rather than as the external 'ticking clock' we think of as time. It offers new insight into the nature of time in quantum gravity that could be used to describe dynamics just as effectively as conventional time."
Future experiments could explore more complicated quantum systems and potentially help simulate aspects of black holes or test competing explanations of how time emerges.