For decades, physicists have debated whether time is a fundamental feature of the universe or an emergent property arising from the interactions of matter. A new laboratory experiment has provided the first controlled evidence supporting the latter idea. By constructing a miniature quantum “universe” from ultracold atoms, researchers demonstrated that time can emerge entirely from changes occurring within an isolated system, without relying on an external clock, tells Live Science.
The experiment, led by physicist Giovanni Barontini at the University of Birmingham, used approximately 24,000 rubidium atoms cooled to just billionths of a degree above absolute zero. The atoms were confined in a sealed quantum system and divided into two regions, an observed “bright” sector and an unobserved “dark” sector. This arrangement mimics certain cosmological theories in which the universe exists without an external reference for time.
Rather than measuring time conventionally, the researchers introduced the concept of “entropic time.” As atoms moved between the two sectors, changes in entropy, the degree of disorder within the system, created an internal measure of time. The experiment revealed that this internal clock behaved much like ordinary time: it established a clear sequence of events, accelerated when entropy changed rapidly, slowed as entropy flow decreased, and effectively stopped once the system reached equilibrium.
The findings also demonstrated that quantum mechanics remains mathematically consistent under this framework. Using entropic time, the team successfully derived a version of the Schrödinger equation that accurately described the evolution of the quantum system. This suggests that internal changes alone may be sufficient to explain the dynamics of isolated quantum systems without invoking an external time parameter.
Although the experiment does not prove that time itself is an illusion, it provides a practical way to investigate questions previously confined to theoretical physics. The laboratory platform could help researchers explore quantum gravity, the origins of the universe, and the relationship between entropy and the arrow of time. By transforming abstract concepts into measurable experiments, the study opens a new avenue for understanding one of physics’ most fundamental mysteries: why time exists and why it always appears to move forward.