Time emerges from changes within the system, not from an external clock
At the University of Birmingham, physicists have demonstrated something that quietly reshapes our understanding of existence itself: time, rather than being a fixed backdrop against which events unfold, may be something that arises from within a system as it changes. Using 24,000 ultracold atoms sealed in isolation, the researchers showed that a coherent arrow of time can emerge purely from the spread of disorder among particles — no external clock required. This experiment, the first of its kind, gives physical grounding to long-standing theoretical suspicions that time is not woven into the universe but is instead a relationship, a consequence of things becoming different from what they were.
- One of physics' deepest tensions — that its laws run equally well forward and backward in time, yet we experience time as strictly one-directional — has been brought into a laboratory for the first time.
- A sealed cloud of 24,000 atoms chilled near absolute zero began mimicking the universe itself, expanding and contracting like a miniature Big Bang and Big Crunch, with no outside reference to tell it what time it was.
- The team found that as atoms shifted between illuminated and dark regions, the changing distribution of disorder produced a consistent, measurable flow — what they call entropic time — that could even speed up or slow down depending on how the system evolved.
- The Schrödinger equation, quantum mechanics' foundational tool, was successfully rewritten using this internal entropic time, proving the framework holds even when time is defined from within rather than imposed from without.
- What had been confined to the abstract mathematics of quantum cosmology — the Wheeler-DeWitt equation, theories of quantum gravity — has now landed in a controlled experimental setting, opening a path toward laboratory tests of the Big Bang, black holes, and the origin of time itself.
A team at the University of Birmingham has built what amounts to a miniature universe: 24,000 atoms cooled to a few billionths of a degree above absolute zero, sealed entirely from the outside world. Inside this quantum chamber, they observed something remarkable — time emerging not from any external clock, but from the atoms themselves, from the way disorder spread and shifted as particles moved between two laser-defined regions. The finding, published in Physical Review Research, challenges the assumption that time is fundamental to reality, suggesting instead that it arises only when things change.
For decades, the Wheeler-DeWitt equation — a cornerstone of quantum cosmology — has described the universe as a single quantum state with no built-in external clock, implying that the familiar flow of time must emerge from relationships within the system itself. Professor Giovanni Barontini and his team set out to test this in the lab. Their apparatus divided an ultracold atomic cloud into a bright observed region and a dark unobserved one, then left the whole system in complete isolation. The bright region expanded and contracted, echoing the hypothetical rhythm of a Big Bang and Big Crunch, while the researchers reconstructed the sequence of events using only information from within — no outside reference required.
What they found was that time emerged from entropy: as the distribution of atoms shifted, those changes marked the passage of what Barontini calls entropic time. When the distribution stopped changing, time effectively stopped. The flow was consistent and one-directional, producing a clear arrow of time — and it could speed up or slow down depending on how entropy was redistributed, revealing time as something malleable rather than fixed. The team also showed that the Schrödinger equation could be rewritten using this internal entropic time without losing its predictive power.
The deeper significance lies not just in the idea but in the fact that it can now be tested. Concepts once confined to theories about the entire cosmos have been demonstrated under controlled conditions for the first time. Barontini and his colleagues suggest the approach could be extended to more complex systems, eventually allowing physicists to probe the physics of the Big Bang, simulated black holes, and competing theories of time's nature — moving what was once purely mathematical speculation into the realm of experimental science.
A team of physicists at the University of Birmingham has built something that sounds like science fiction: a miniature universe made of 24,000 atoms, chilled to a few billionths of a degree above absolute zero, sealed off from the outside world. Inside this quantum chamber, they watched time emerge not from any ticking clock, but from the atoms themselves—from the way disorder spreads and contracts as particles shift between two regions. The finding, published in Physical Review Research, challenges a foundational assumption about reality: that time is woven into the fabric of existence. Instead, it suggests time might be something that arises only when things change.
For decades, certain theories of quantum gravity have hinted at this possibility. The Wheeler-DeWitt equation, a cornerstone of quantum cosmology, describes the universe as a single quantum state with no external clock built in. If this is true, then the familiar sensation of time flowing from past to future—the arrow of time we experience every moment—must somehow emerge from the relationships between different parts of the system itself. But this remained largely theoretical, a mathematical curiosity without experimental proof. Professor Giovanni Barontini and his team set out to test it in the lab.
Their apparatus was elegant in its simplicity. They created a cloud of ultracold atoms and divided it with two laser beams of different frequencies, producing a bright region (observed) and a dark region (unobserved). The whole system was completely isolated from the laboratory outside. Then they watched. The bright region expanded and contracted, mimicking in miniature the hypothetical Big Bang and Big Crunch—the expansion and eventual reversal of the universe itself. Because nothing could enter or leave the system, the researchers could reconstruct the sequence of events using only information from within the mini universe. No external clock needed.
What they found was striking: time emerged from entropy, the measure of disorder or spread among the atoms. As particles moved between the bright and dark regions, the distribution of atoms changed. These changes marked the passage of what Barontini calls entropic time. When the distribution stopped changing, time effectively halted. The flow was consistent and one-directional—it produced a clear arrow of time, ordering events correctly even as the system expanded and contracted. Remarkably, this entropic time could speed up or slow down depending on how the entropy was redistributed, suggesting time is not a fixed constant but something malleable, dependent on what is happening inside the system.
The implications ripple outward. Barontini noted that in everyday life, time flows from past to future, yet most of the basic laws of physics work equally well in both directions. This asymmetry has long puzzled physicists. If time is not fundamental—if it emerges only from change—then the arrow of time is not a mystery to be solved but a natural consequence of how systems evolve. The team also demonstrated that the Schrödinger equation, the bedrock of quantum mechanics, can be rewritten using entropic time instead of an external clock. This means scientists can still predict how a quantum system evolves, even when time is defined by internal changes rather than by a ticking background.
What makes this work significant is not just the idea, but the fact that it can now be tested. For the first time, concepts normally confined to theories about the entire universe—how time emerges in quantum gravity—have been demonstrated under controlled laboratory conditions. The mini universe is a proof of concept, a way to bring the abstract into the tangible. Barontini and his colleagues suggest the same approach could be expanded to more complex quantum systems, eventually allowing physicists to investigate the physics of the Big Bang, the Big Crunch, simulated black holes, and competing theories about the nature of time itself. What was once purely mathematical speculation may soon become experimental science.
Citações Notáveis
Time can be defined by changes within a system rather than as the external ticking clock we think of as time, offering new insight into quantum gravity.— Professor Giovanni Barontini
A Conversa do Hearth Outra perspectiva sobre a história
So they're saying time doesn't exist until something changes?
Not quite. They're showing that in a quantum system, time can emerge from the changes happening inside it, rather than being imposed from outside. It's a different way of thinking about what time is.
But we experience time as constant, always moving forward. How does that fit?
That's the puzzle they're addressing. In their mini universe, time flows in one direction because entropy—disorder—increases in a consistent way. The arrow of time comes from that internal asymmetry, not from some cosmic clock ticking away.
Why does this matter for physics?
Because if time isn't fundamental to the universe, it changes how we think about quantum gravity and the Big Bang. It means time might be something that emerges from the relationships between parts of a system, not something that exists independently.
Can they actually use this to understand the real universe?
That's the next step. They've shown it works in a controlled lab setting with ultracold atoms. If they can scale it up and make it more complex, they might be able to test theories about black holes and the early universe experimentally instead of just mathematically.
So this is the beginning of something larger?
Exactly. It's a proof that these ideas about time can be tested in the real world. That opens a door that was mostly theoretical before.