Time may not be woven into reality—it emerges from change
In a Birmingham laboratory, physicists have built a sealed cosmos of 24,000 ultracold atoms that expands and contracts like a universe in miniature — and within it, they found that time does not arrive from outside, but grows from within. By watching how particles rearranged themselves across hidden and visible regions, the team demonstrated that the arrow of time may be nothing more than the signature of entropy in motion. The experiment transforms one of philosophy's oldest questions — why does now follow then? — into something a laboratory can begin to answer.
- Physics has long carried an open wound: its fundamental laws run equally well forward and backward in time, yet we experience time as a one-way street — and no equation has fully explained why.
- A team at the University of Birmingham sealed 24,000 atoms near absolute zero into a miniature cosmos, deliberately cutting it off from all external clocks to force the question of where time actually comes from.
- Inside the system, time emerged not from any ticking mechanism but from entropy — the shifting distribution of particles between a visible and a hidden region — and it consistently pointed in one direction across repeated Big Bang–Big Crunch cycles.
- The researchers rewrote the Schrödinger equation itself using entropic time and showed it still works, turning what was once a philosophical reframing into a functioning mathematical framework.
- The experiment opens a laboratory door to questions previously trapped in theory — quantum gravity, early universe conditions, black hole simulations — giving physics a place to test ideas that have lived only on chalkboards.
In a laboratory at the University of Birmingham, physicists have built something quietly extraordinary: a miniature universe. Twenty-four thousand atoms, chilled to billionths of a degree above absolute zero, were sealed into a quantum system and divided by laser beams into two regions — one visible to the researchers, one deliberately hidden. Inside this sealed cosmos, the bright region expanded and contracted in cycles echoing the theoretical Big Bang and Big Crunch. And because the system was entirely isolated from the outside world, the team had no external clock to consult. They had to reconstruct the passage of time from within.
What they found was that time emerged from entropy — from the way particles distributed themselves between the two regions. When the distribution shifted, time moved. When it stilled, time froze. Remarkably, this internally generated time flowed in one consistent direction across every cycle, correctly ordering events even as the system repeatedly collapsed and rebegan. Its pace could quicken or slow depending on how fast entropy was changing, but the arrow never reversed.
This concept of entropic time strikes at one of physics' most enduring puzzles. The fundamental laws of the universe are largely indifferent to direction — they work the same run forward or backward. Yet we live inside an unmistakable before and after. Giovanni Barontini, who led the research, framed the question plainly: in theories of quantum gravity, time has no built-in presence, yet in lived experience it flows without pause. Why?
The team's answer, published in Physical Review Research, was not merely philosophical. They rewrote the Schrödinger equation using entropic time in place of conventional time and showed it could still generate accurate predictions about quantum probability distributions. The mathematics held. What had been an abstract debate about the nature of time became a working scientific framework — and, more significantly, a laboratory platform. Questions about quantum gravity, the early universe, and even black hole behavior, long confined to theory, now have a place where they might be tested.
In a laboratory at the University of Birmingham, physicists have constructed something that resembles a universe in miniature—a sealed quantum system containing 24,000 atoms chilled to billionths of a degree above absolute zero. What they discovered inside challenges a fundamental assumption about reality: that time is woven into the fabric of existence itself. Instead, their experiment suggests time may be something that emerges from change, a byproduct of how matter and energy shift within a system rather than an external clock ticking away in the background.
The setup was elegant in its simplicity. Two laser beams divided the cloud of ultracold atoms into two regions—one observable to the researchers, one deliberately hidden from view. Inside this sealed cosmos, the bright region repeatedly expanded and contracted in cycles that mimicked the theoretical Big Bang followed by a Big Crunch, the scenario in which the universe's expansion eventually reverses direction. Because the system was completely isolated from the outside world, the team could not rely on laboratory clocks to measure what was happening. Instead, they had to reconstruct the sequence of events using only the changes occurring within the mini-universe itself.
What they found was that time emerged from entropy—the way particles distributed themselves across the system. As atoms moved between the bright and dark regions, the arrangement of matter shifted. These shifts marked the passage of time. When the distribution stopped changing, time effectively froze. Remarkably, this version of time flowed consistently in one direction, correctly ordering events even as the system cycled through repeated expansions and contractions. The pace of time could accelerate or decelerate depending on how rapidly entropy was changing, but the arrow always pointed forward.
This concept, called entropic time, addresses one of physics' deepest puzzles. Most of the fundamental laws governing the universe work equally well in either direction—forward or backward. Yet we experience time as flowing relentlessly from past to future. If the universe has no built-in clock, no external timekeeper, how do events arrange themselves into a meaningful sequence of before and after? Giovanni Barontini, who led the research, posed the question directly: "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?"
The team's work, published in Physical Review Research, went further than simply observing this phenomenon. They demonstrated that quantum mechanics remains mathematically consistent under this framework. They rewrote the Schrödinger equation—one of the foundational equations of quantum physics—using entropic time instead of conventional time, and showed it could make predictions about how quantum probability distributions evolve. This was not merely a philosophical reframing; it was a working mathematical system.
What makes this experiment significant is that it transforms decades of abstract theoretical debate into testable science. Questions about the nature of time in quantum gravity, about the conditions of the early universe, about whether black holes can be simulated in a laboratory—these have long existed mainly on chalkboards and in complex equations, too far removed from experiment to verify. Now physicists have a platform to investigate them. The miniature universe could eventually allow researchers to probe competing theories of quantum gravity, explore the physics of the early cosmos, and even create controlled simulations of black holes. For the first time, some of the deepest questions in physics have a laboratory where they might be answered.
Citas Notables
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?— Giovanni Barontini, University of Birmingham
La Conversación del Hearth Otra perspectiva de la historia
So they built a universe out of atoms. How does that actually work?
They took 24,000 atoms and cooled them to near absolute zero, then trapped them in a sealed quantum system. Two laser beams split it into two regions—one they could observe, one they couldn't. It's simplified, but it has the essential ingredients: matter, dynamics, isolation from the outside.
And time just... emerged from it?
Not spontaneously. They watched how the atoms moved between the two regions, how the distribution of matter changed. Those changes—entropy increasing or decreasing—that's what they identified as time. When nothing changed, time stood still.
But we have clocks. We measure time. Why does this matter?
Because clocks are external. They assume time already exists. This experiment suggests time might not be fundamental at all—it might be something that arises from the internal dynamics of any system. That's a completely different way of thinking about reality.
Does it work? Can you actually use this entropic time to predict things?
Yes. They rewrote the Schrödinger equation using it. The math works. It makes predictions about quantum systems just as well as conventional time does.
What's the practical payoff?
Right now, it's mostly theoretical validation. But the platform they've built could let physicists test quantum gravity theories, simulate black holes, explore the early universe—all things that have been pure mathematics until now. They've moved the conversation from the chalkboard into the lab.