Quantum experiment uses shifting atom distributions to measure time
The study found that an internally defined measure could order events during expansion and contraction, without requiring an outside clock.
Changes among approximately 24,000 atoms can provide a quantum system with its own measure of time, according to research published in Physical Review Research. Professor Giovanni Barontini of the University of Birmingham demonstrated the approach in a laboratory experiment that tracked particle distributions rather than an external clock.
The experiment confined ultracold atoms within an isolated system. A pair of lasers, each operating at a different frequency, formed a barrier between observed and unobserved regions. Particles could cross that boundary, changing their distribution in the observed region as it repeatedly expanded and contracted.
Barontini termed the resulting measure “entropic time.” It advanced whenever the particle distribution became either more dispersed or less dispersed. With no change in that distribution, the internal measure paused, although laboratory time did not stop.
The study found that this measure maintained the ordering of events and progressed in a single direction, while its pace varied according to entropy changes. Barontini also showed that the Schrödinger equation could be expressed in a form using entropic time to describe quantum evolution.
The expansion and contraction modeled simplified aspects of the Big Bang and the hypothetical Big Crunch; neither cosmic event was recreated. The findings offer an experimental approach to studying theories of emergent time, but do not prove that time is absent as a fundamental feature of the universe.
