Scientists Built A Tiny ‘Universe’ And Let Time Grow Inside It

No Clock Needed: Physics Experiment Hints Time Creates Itself

What if time isn’t actually a fundamental feature of the universe, but something that emerges from it, the way heat emerges from friction? That’s one of the deepest unsolved puzzles in physics, and for decades it lived entirely in the realm of theory. Now, a physicist at the University of Birmingham has built a miniature laboratory “universe” using ultra-cold atoms to test that idea. According to the study, published in Physical Review Research, the results suggest that something functioning like time can emerge from a system’s own internal disorder, with no outside clock needed.

That puzzle sits at the heart of a longstanding clash in modern physics. Quantum mechanics describes the world at the subatomic scale; general relativity governs gravity and the large-scale structure of the cosmos. When physicists try to combine them into a single theory of quantum gravity, time has a way of disappearing from the equations entirely. A famous equation in this field, known as the Wheeler-DeWitt equation, describes the universe as a whole but contains no built-in clock, no external “tick” that drives change forward.

This mismatch is called the “problem of time,” and it has haunted theoretical physics for over half a century. One proposed solution is that time is relational, meaning it doesn’t exist on its own, but only as a relationship between different parts of a system. One part of the universe acts as a clock, and everything else is described relative to it. Testing that idea experimentally has been nearly impossible.

A Universe in a Trap

Physicist Giovanni Barontini created what his paper describes as a “mini-universe,” a cloud of roughly 24,000 rubidium atoms chilled to near absolute zero, where the laws of quantum physics take hold. He confined the cloud inside a laser-beam trap, then divided it using a thin wall of light about 8 micrometers wide. This created a “bright sector” that could be directly observed and a “dark sector” left unobserved, with the whole setup kept carefully isolated from outside interference. Atoms could slosh back and forth between sectors depending on how high the barrier was set, like water flowing between two connected containers.

Big Bang, Big Crunch, Repeat

Watched through the lens of a standard laboratory clock, the bright sector’s behavior looked almost cosmic. Atoms flooded in from the dark sector in what Barontini calls a “big bang,” expanded outward, reached a maximum size, then contracted and collapsed back in a “big crunch.” Barontini followed the dynamics for 120 milliseconds, taking a snapshot every 2 milliseconds, and repeated the experiment at different barrier heights to vary how freely matter could flow between zones.

Entropy is a measure of disorder. The second law of thermodynamics holds that entropy in isolated systems tends to grow, and that tendency is physics’ clearest clue for why time seems to have a direction. As atoms crossed the barrier, the bright sector’s entropy shifted, giving Barontini the raw material to build an “entropic time.”

Building a Clock From Chaos

Rather than measuring time with an external clock, Barontini constructed a new measure of time purely from changes happening inside the system. When entropy flows freely between sectors, this internal time moves quickly. When entropy exchange slows or stops, this internal time freezes, even if the laboratory clock keeps ticking.

When plotted against external laboratory time, this entropic time grew in one direction almost everywhere across all runs. More importantly, it robustly ordered the events of the bright sector, sequencing the big bang-like expansion and big crunch-like collapse, with only a few small “wiggles” in the data. One notable result: between a big crunch and the next big bang, no entropy was exchanged, so no entropic time elapsed at all. From the perspective of this entropic clock, that gap simply did not register.

When the barrier was set high, entropy exchange slowed to nearly nothing and the bright sector settled into a “heat death,” a near-stationary state where entropic time stops. When it was lowered, the cycling was vigorous and the entropic time flowed most rapidly.

Barontini then built a mathematical model using entropic time in place of a lab clock and ran its predictions against the actual data. For the primary test case, the match was close, adding weight to the idea that this internally built clock is more than a mathematical convenience.

Cold Atoms Give Physics Its First Testbed for Relational Time

This is a quantum simulator, not a direct window into the cosmos. The atom cloud obeys well-understood quantum mechanics, not the full equations of general relativity, and the results don’t resolve the problem of time in the actual universe. What they do show is that the relational-time idea holds up in a precisely controlled setting, and for the first time gives physicists real experimental data to test it against.

Within this experiment, a meaningful sense of time, with direction, pace, and the ability to order events, emerged from nothing but the system’s own internal workings. Whether the universe at large operates by the same principle remains an open question, but now, at least, that principle has a concrete, testable model to point to.

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