QUANTUM PHYSICS • ENTROPY • TIME
Can Ultracold Atoms Keep Their Own Time?
Giovanni Barontini’s cold-atom experiment tests relational time: ordering events through changes inside a quantum system.
ADDED OCTOBER 31, 2026 • PAPER PUBLISHED JUNE 11, 2026
A laboratory test of an old question
Giovanni Barontini at the University of Birmingham used an ultracold atomic system to test whether changes inside a system can supply a useful measure of time. The paper, Testing the problem of time with cold atoms, appeared in Physical Review Research in June 2026. Recent coverage should not be mistaken for a new October publication.
What the experiment actually did
The university describes a cloud of about 24,000 rubidium atoms cooled to billionths of a degree above absolute zero. An optical barrier divided the trapped cloud into observed (“bright”) and unobserved (“dark”) sectors, with atoms able to move between them.
The paper describes a well-isolated Bose–Einstein condensate with negligible dissipation over the experimental timescale. The observed sector underwent repeated expansion and recollapse. From a measured, coarse-grained entropy, Barontini constructed an internal “entropic time” that consistently ordered the observed events.
An effective Schrödinger equation expressed using that internal time reproduced the measured evolution. The experiment therefore provides a platform for comparing relational descriptions of time with laboratory data.
What “mini-universe” means here
It is an analogy for a controlled physical model, not a newly created cosmos. The work is motivated by the problem of time in approaches such as the Wheeler–DeWitt framework, where a universal external clock is absent.
The boundary of the result
The study tests a particular way to define time through internal change. It does not establish that all time in our universe is emergent, solve quantum gravity, or show that ordinary clocks cease to work. Calling it proof that time is nonfundamental goes beyond what the experiment establishes.
Why it matters
MKP interpretation: A difficult foundational question becomes more productive when researchers turn it into something measurable. The interesting advance is the comparison between an internal ordering rule and real atomic dynamics.
Discussion
If you could observe only changes inside a sealed room, what could you use as a clock? How would you check whether your chosen measure orders events consistently? What would make a laboratory analogy informative without making it a complete model of the universe?