Physicist creates mini-universe

A physicist has created a "mini-universe" using a quantum system of ultra-cold atoms to explore how time might be defined internally, without needing an external clock. This research challenges the traditional idea that time is a fundamental part of the universe.

Time as an emergent property

The study, led by Giovanni Barontini at the University of Birmingham, suggests time might arise from the behavior of particles and their interactions, rather than being a basic element of the universe. This challenges the common view that time is a fundamental part of space-time, the four-dimensional framework that describes the universe.

Published in a scientific journal

Barontini's findings were published in the journal Physical Review Research. The research explores theoretical ideas, such as the Wheeler-DeWitt equation, which suggest time might not be a basic variable in the universe’s description. This raises questions about how to explain the order of events without an external clock.

Quantum system with ultra-cold atoms

To investigate, Barontini designed a quantum system using a cloud of about 24,000 atoms cooled to just a few billionths of a degree above absolute zero. This extreme cold minimizes thermal movement, allowing the observation of quantum phenomena. The system is isolated and divided into two regions: a visible "bright" region and an invisible "dark" region.

Simulating universe expansion and contraction

The observed region undergoes repeated cycles of expansion and recontraction, mimicking the Big Bang and the hypothetical Big Crunch, where the universe collapses after expanding. This approach allows researchers to simulate cosmological processes on a small scale.

Tracking time through entropy changes

To study time without an external clock, Barontini used changes in entropy, a measure of disorder, to track the system's evolution. Variations in entropy can act as an internal measure of time. When this measure stops changing, the system appears to halt, but this does not mean time itself stops, only that the tracking variable ceases to vary.

Future experiments and implications

Barontini clarifies that the experiment does not claim time is an illusion but shows that a quantum system can define time internally. Future research may test this concept in more complex systems and explore its relevance to quantum gravity and cosmological models.