Physicists Create a 'Mini-Universe' to Study the Arrow of Time
For the first time, researchers have demonstrated experimentally that time can arise from within a system itself, driven by the flow of entropy, rather than being an external, universal clock.
A New Kind of Time
An experiment at the University of Birmingham has produced a "mini-universe" that generates its own internal time. Led by physicist Giovanni Barontini, the team used a Bose-Einstein condensate (BEC)—the fifth state of matter, created by cooling rubidium atoms to billionths of a degree above absolute zero—to model a cyclic cosmos that expands and contracts like a heartbeat.
The system's behavior is governed solely by the exchange of entropy between two halves of the condensate, defining an "entropic time" that only moves forward when entropy flows.
The Experiment: Bright and Dark Sectors
The BEC, consisting of roughly 24,000 atoms, was confined in an optical trap. Researchers then split it into two distinct sectors using a barrier created by two laser beams of different frequencies:
- The 'Bright' Sector: This portion of the condensate was directly observed by the scientists.
- The 'Dark' Sector: This portion remained unobserved.
Atoms naturally oscillated back and forth between these two sectors, creating a rhythmic cycle. This cyclical flow of atoms and entropy mirrored the theoretical cycles of a universe undergoing a Big Bang and a Big Crunch.
"In the experiment, the observed part of the system exchanges atoms and entropy with the unobserved part. From this entropy exchange, we define an internal, 'entropic' time. This time increases when entropy is exchanged, and it stops when the entropy exchange stops."
– Giovanni Barontini
The Arrow of Time from Entropy
The study provides the first controlled experimental evidence that a directional "arrow of time" can be an emergent property of a system, rather than a fundamental background condition. When the exchange of entropy between the bright and dark sectors ceased, the internal "entropic time" effectively stopped.
Barontini summarized the finding in simple terms: "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."
Implications for Cosmology
The highly controllable nature of the experiment—allowing adjustments to the trap's shape, barrier height, atom interactions, density, and coupling between regions—opens a new way to probe fundamental questions about the cosmos.
The researchers suggest the system could be used to test theories about cosmic singularities and the ultimate fate of the universe. "For example, one could ask whether an apparent collapse behaves like a singularity or instead turns into a bounce," Barontini noted, pointing to potential insights into the Big Bang, the Big Crunch, and the nature of black holes.
The groundbreaking research was published in the journal Physical Review Research.