24,000 Cold Atoms Model ‘Mini Universe’ Without a Ticking Clock

A system constructed from 24,000 ultracold rubidium atoms is challenging fundamental assumptions about the nature of time, according to research led by Professor Giovanni Barontini at the University of Birmingham. The experiment creates a hermetically sealed quantum system, cooled to just a few billionths of a degree above absolute zero, that mimics the expansion and collapse of a universe, a “Big Bang and a Big Crunch” on a tiny scale. Barontini’s model directly addresses the Wheeler-DeWitt equation, a theory positing that time doesn’t inherently exist but emerges from relationships within a system, and demonstrates how time can be created from the disorder of atoms. “In some theories of the universe, especially quantum gravity, time doesn’t appear as a built-in feature,” explains Professor Barontini; “This study provides clear experimental evidence that ‘time’ can be defined by changes within a system rather than as the external ‘ticking clock’ we think of as time.”

Professor Giovanni Barontini’s experiment isolates the atoms within a hermetically sealed quantum system, divided by a laser-formed barrier into ‘bright’ and ‘dark’ regions, allowing observation of internal changes without external timing mechanisms. The core of the investigation centers on the concept of ‘entropic time’, derived from the disorder, or entropy, of the atoms and their movements within the isolated system. Barontini’s team demonstrated that as the distribution of particles in the ‘bright’ sector changed, with atoms moving in or out, the system registered forward movement in time, while a static distribution signified temporal stasis. The experiment also shows that the main equation in quantum mechanics, the Schrödinger equation, can be generalized using this internally generated ‘entropic time’, accurately describing the dynamics of the quantum system.

Professor Giovanni Barontini and colleagues at the University of Birmingham have demonstrated a novel approach to defining time, moving beyond the conventional reliance on external clocks and instead grounding it in the internal dynamics of a quantum system. This system, divided into ‘bright’ and ‘dark’ regions by a laser barrier, allowed researchers to observe the behavior of atoms as they traversed between sectors, effectively modeling a simplified cosmos. Barontini’s work builds on the Wheeler-DeWitt equation, a theoretical framework suggesting time isn’t a fundamental aspect of the universe, but rather emerges from relationships between its constituent parts. The researchers found that ‘entropic time’, defined by the disorder, or entropy, of the atomic system, could be measured by tracking the spread of particles as they moved between regions. Why, in everyday life, does time flow from past to future when most basic laws of physics work the same way forwards and backwards? This research offers a new avenue for understanding time’s nature within the complex realm of quantum gravity, demonstrating that changes in the distribution of atoms, specifically the spread of entropy, can define a directional ‘entropic time’ even when the system appears static.