Plate Nº 41 · recorded October 30, 2026
PhysicsReported finding
24,000 Atoms Build a Tiny Universe Where Time Runs Without a Clock
Birmingham physicists used 24,000 ultracold atoms to build a tiny expanding universe where time emerged from entropy alone, no external clock required — first evidence of its kind.
By Elena Vasquez4 min read860 words
In brief
- Professor Giovanni Barontini used about 24,000 ultracold atoms to build an isolated quantum system mimicking Big Bang and Big Crunch cycles.
- The findings were published October 30, 2026, in Physical Review Research (DOI: 10.1103/1h9j-df4k).
- Atoms were cooled to a few billionths of a degree above absolute zero.
- The experiment defines 'entropic time' via changes in particle distribution, giving it an arrow of time without an external clock.
- A version of the Schrödinger equation can be expressed using entropic time, enabling standard quantum predictions.
A University of Birmingham researcher built a miniature universe from roughly 24,000 ultracold atoms and watched a form of time emerge without any external clock. The experiment, published October 30, 2026, in Physical Review Research, offers the first controlled experimental evidence that time can be defined purely by changes inside a quantum system.
Professor Giovanni Barontini cooled a cloud of atoms to a few billionths of a degree above absolute zero, where quantum effects dominate. Lasers confined the system and split it into two regions. The work suggests time may not be a fundamental ingredient of reality. Instead, it could arise from relationships and changes within the universe itself.
Why doubt that time is fundamental?
Everyday intuition says time flows forward regardless of what happens around us. Physics is less sure.
Some theories that try to unite quantum mechanics with gravity, such as the Wheeler-DeWitt equation, describe the universe as a single, unchanging quantum state. In that picture, there's no built-in clock and no external time variable ticking away.
That creates a puzzle. If the universe has no external clock, what determines the order of events? What comes first, what comes later? One proposed answer: time emerges from the changing relationships between parts of the universe. Barontini set out to test whether that process could be observed in a lab.
How do you build a tiny universe?
The recipe starts with about 24,000 atoms chilled to nearly absolute zero. At such temperatures, researchers can study quantum behaviors that are normally hidden.
The setup had three key features:
- An isolated quantum system cut off from its surroundings
- Two laser beams at different frequencies forming a thin barrier
- That barrier dividing the system into a 'bright' observed region and a 'dark' unobserved one
Atoms could move between the two regions even though the whole system stayed isolated from the outside world.
The bright region repeatedly expanded and contracted. The expansion mimicked a simplified Big Bang. The contraction resembled a Big Crunch, the hypothetical fate in which cosmic expansion reverses and everything collapses inward. The experiment didn't recreate actual cosmic events. It built a simplified quantum model where researchers could reconstruct a sequence of events without referring to any clock outside the system.
What is 'entropic time'?
The key was entropy, the physics term for how spread out or disordered particles and energy are. Barontini tracked time through changes in how atoms were distributed in the bright region, not through seconds or minutes.
As atoms crossed between bright and dark regions, the particle distribution shifted. Those shifts defined the system's progression. When the spread of the distribution increased or decreased, this internal time moved forward. When the distribution held steady, the internal measure of time effectively stopped — though ordinary time in the laboratory kept running.
Barontini calls the concept 'entropic time,' and it showed three notable properties:
- It moves consistently in one direction, establishing an 'arrow of time' — the distinction between past and future
- It places events in the correct sequence even as the tiny universe expands and contracts
- It doesn't advance at a constant rate; it can speed up or slow down depending on how entropy changes
The bottom line: order emerged from within, no external ticking required.
Why does this matter?
Barontini said: 'In some theories of the universe, especially quantum gravity, time doesn't appear as a built-in feature. Yet in everyday life, time flows from past to future — why is this so, when most basic laws of physics work the same way forwards and backwards?'
He added: 'This study provides the first controlled experimental evidence that "time" can be defined by changes within a system rather than as the external "ticking clock" we think of as time. It offers new insight into the nature of time in quantum gravity that could be used to describe dynamics just as effectively as conventional time.'
The finding goes beyond ordering events. Barontini showed that a version of the Schrödinger equation — the foundational quantum-mechanics equation describing how a system's quantum state evolves — can be written using entropic time. The internal measure could predict the system's behavior much as conventional time does in standard quantum mechanics.
Could this explain the Big Bang?
For decades, questions about time's origin belonged to theoretical fields like quantum cosmology and quantum gravity, which study conditions where quantum effects and gravity act together, as in the early cosmos. Barontini's tabletop universe gives physicists a system they can create, manipulate and observe.
Future experiments could extend the approach to more complex quantum systems, modeling the Big Bang and Big Crunch in finer detail. Similar techniques might eventually simulate aspects of black holes or help distinguish between competing explanations of how time emerges.
Be clear about limits. The experiment doesn't prove time is an illusion or that our universe lacks fundamental time. What it demonstrates is something previously hard to test: a quantum system can carry a meaningful internal measure of time without an external clock. That's a new tool for a question that has challenged physicists and philosophers for centuries — what makes time flow?
via dx.doi.org (Original)
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Correspondent covering money, funding and market shifts around general science news at SciBeat.
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