Time seems like one of the most basic parts of everyday life. We use clocks to measure it, plan our days around it, and experience it as a steady flow from the past into the future.
But according to some of the deepest theories in physics, time may not actually exist in the way we think it does.
Now, a scientist at the University of Birmingham has taken an important step toward exploring this mystery.
Professor Giovanni Barontini has created a tiny laboratory “universe” that shows how time might emerge naturally from changes within a system, even when no clock is present.
His findings were published in Physical Review Research.
Some theories that attempt to explain the entire universe suggest that time is not a fundamental feature of reality.
One example is the Wheeler–DeWitt equation, which describes the universe as a single quantum state without any built-in clock. In this view, the universe simply exists, and our sense of time must somehow arise from relationships between its different parts.
To investigate this idea, Barontini created a miniature quantum universe using about 24,000 ultracold atoms. These atoms were cooled to temperatures only a few billionths of a degree above absolute zero, making them behave according to the strange rules of quantum physics.
The atoms were trapped inside a sealed system and divided into two regions by laser beams. One region was visible to researchers and called the “bright” sector, while the other remained unobserved and was called the “dark” sector.
Inside this tiny universe, the bright region repeatedly expanded and contracted, somewhat resembling the birth and collapse of a cosmos. Scientists could reconstruct the sequence of events occurring inside the system without referring to any external clock.
The key discovery was that a form of time emerged naturally from changes in the arrangement of the atoms. As atoms moved between the bright and dark regions, the amount of disorder in the system changed. Physicists call this disorder “entropy.”
Barontini found that when entropy changed, the system effectively moved forward in time. When the distribution of atoms remained unchanged, time appeared to stop. He called this concept “entropic time.”
Remarkably, this entropic time behaved much like the time we experience every day. It moved in a single direction, creating a clear arrow of time from past to future. It also correctly ordered events and could speed up or slow down depending on how entropy changed within the system.
The study provides the first controlled experimental evidence that time can emerge from internal changes rather than from an external ticking clock.
Perhaps most importantly, the experiment allows scientists to test ideas about the nature of time that were once limited to theoretical discussions about the universe itself. In the future, similar systems could help researchers explore the physics of the Big Bang, simulate black holes in the laboratory, and test competing theories about how time first emerged in our universe.
The work suggests that time may not be a fundamental ingredient of reality after all, but something that arises from the changing relationships between the things around us.
