Physicist Creates Mini-Universe to Test Whether Time Emerges from Entropy

Giovanni Barontini, physicist at the University of Birmingham, assembled a miniature analogue of a universe with roughly 24,000 rubidium atoms cooled to billionths of a kelvin above absolute zero. The atoms formed a Bose-Einstein condensate confined in a dipole optical trap split by intersecting laser beams into a bright observable sector and a dark unobserved sector, allowing atoms to oscillate between them.

ScienceAlert

Quantum mechanics and general relativity suggest that time may not be a fundamental variable, a view reinforced by the Wheeler-DeWitt equation, which omits time entirely. By contrast, the second law of thermodynamics provides an arrow of time through increasing entropy, offering a possible basis for temporal ordering.

ScienceAlert

In Barontini’s system, the observable sector exchanges atoms and entropy with the dark sector. He defines an internal “entropic” time that increases while entropy is transferred and halts when exchange stops. This internal clock derives its direction from the entropy flow, removing the need for an external time parameter.

ScienceAlert

The rhythmic oscillation of atoms mimics theoretical cycles of a universe expanding (Big Bang) and contracting (Big Crunch). Adjusting trap geometry, barrier height, inter-atomic interactions, and density profiles lets the platform simulate conditions analogous to singularities, bounces, or black-hole horizons. The experiment thus offers a quantitative testbed for probing quantum-gravity questions that have been largely mathematical.

ScienceAlert

Barontini says the experiment provides controlled evidence that time can be defined by internal changes rather than an external ticking clock, and that the entropic time follows the thermodynamic arrow, ensuring forward-only ordering of events. He notes the system’s flexibility for probing cosmological scenarios and for informing attempts to reconcile general relativity with quantum mechanics.

ScienceAlert

• “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,” — Giovanni Barontini, physicist, University of Birmingham

ScienceAlert

• “From this entropy exchange, we define an internal, 'entropic' time," Barontini told ScienceAlert.” — Barontini

ScienceAlert

• “A simplified way to say it is: the mini-universe does not need an external parameter to order the events; its own entropy flow tells which event comes next," Barontini said.” — Barontini

ScienceAlert

Barontini proposes varying trap shape, barrier height, and interaction strength to test whether a collapse behaves like a singularity or produces a bounce. Extending the platform to isolate atoms on one side could approximate black-hole boundaries, enabling experimental study of phenomena that have so far been purely theoretical.

ScienceAlert