For centuries, physicists have treated time as one of the universe’s most fundamental ingredients. But what if time isn’t something that exists independently? What if it only appears because things change? A new experiment from researchers at the University of Birmingham offers intriguing evidence that this idea may be more than philosophical speculation. By creating a miniature quantum “universe” containing 24,000 ultracold atoms, scientists observed something remarkable: a measurable sense of time emerged naturally from changes inside the system itself—without relying on any external clock.
The findings, published in Physical Review Research, could help scientists better understand one of the deepest puzzles in modern physics and provide an experimental platform for testing ideas that were previously confined to theoretical models.
Why do some physicists believe time may not be fundamental?
In everyday life, time seems obvious. Clocks tick, calendars advance, and causes always appear before effects.
Modern physics, however, paints a more complicated picture.
Einstein’s theory of relativity already showed that time is not universal—it can slow down or speed up depending on gravity and velocity. Quantum gravity theories go even further, suggesting that time itself may not be a basic property of reality.
One of the most famous examples is the Wheeler-DeWitt equation, which describes the entire universe as a single quantum state without an external clock. In this framework, time does not explicitly appear in the equations governing the universe.
Instead, what we perceive as the flow of time may emerge from relationships between different parts of a quantum system.
The challenge has always been testing this idea experimentally.
How did scientists create a miniature quantum universe?
To investigate whether time can emerge naturally, Professor Giovanni Barontini and his team built an isolated quantum system using approximately 24,000 ultracold atoms.
The atoms were cooled to only a few billionths of a degree above absolute zero, minimizing outside disturbances.
Researchers then used two laser beams to divide the cloud of atoms into two regions:
- A “bright” region that could be observed.
- A “dark” region that remained hidden from direct observation.
Together, these regions formed a simplified laboratory model of a self-contained quantum universe.
Unlike most laboratory experiments, the researchers deliberately avoided relying on an external clock to determine how the system evolved.
Instead, they examined only what happened inside the miniature universe.
How did time emerge without a clock?
Inside the isolated system, the bright region repeatedly expanded and contracted.
Researchers likened this behavior to a simplified version of cosmological expansion and contraction—similar to the concepts of a Big Bang followed by a hypothetical Big Crunch.
Because the system was completely isolated, scientists reconstructed the sequence of events using only information generated within the quantum system itself.
Their results showed that time appeared to emerge from internal changes rather than from an independent background clock.
In other words, change itself became the measure of time.
What is entropic time?
The experiment introduces the idea of “entropic time.”
Rather than measuring seconds with a clock, time was defined by changes in entropy—the redistribution or spread of atoms between the bright and dark regions.
As the particle distribution changed, the system effectively moved forward in time.
When the distribution stopped evolving, time effectively stopped as well.
According to the researchers, this emergent form of time displayed several familiar properties:
- It moved in a single direction, creating an “arrow of time.”
- It correctly ordered events.
- It could speed up or slow down depending on how quickly entropy changed.
This suggests that the passage of time may be closely tied to the evolution of physical systems rather than existing independently.
Why is entropy important?
Entropy is often described as a measure of disorder, although physicists more accurately define it as the number of possible microscopic arrangements of a system.
Entropy already plays a central role in explaining why time seems to move only forward.
For example:
- Ice cubes melt rather than spontaneously reform.
- Cream mixes into coffee but never naturally separates again.
- Eggs break but do not reassemble themselves.
These everyday processes all involve increasing entropy.
The new experiment extends this idea by suggesting that entropy doesn’t merely indicate the direction of time—it may actually provide the foundation for defining time itself inside an isolated quantum system.
Why does this matter for quantum gravity?
One of the biggest unsolved problems in physics is reconciling quantum mechanics with Einstein’s theory of gravity.
Quantum mechanics describes extremely small particles.
General relativity explains gravity and the large-scale structure of the universe.
Although both theories are extraordinarily successful, they remain fundamentally incompatible.
One reason is that quantum mechanics assumes time already exists, while several approaches to quantum gravity do not.
This experiment offers a possible bridge.
It demonstrates that conventional quantum evolution can still be described even when time is defined internally rather than supplied by an external clock.
That makes it one of the first laboratory demonstrations of an idea previously explored mainly through mathematics.
Could this help scientists understand the Big Bang?
Potentially, yes.
The researchers believe their miniature universe could become a valuable testing ground for ideas related to:
- The earliest moments after the Big Bang.
- Quantum cosmology.
- Black hole physics.
- The emergence of spacetime.
- Competing theories of quantum gravity.
Instead of relying solely on equations, scientists may eventually test aspects of these theories experimentally using increasingly sophisticated quantum systems.
While these laboratory models do not recreate the actual universe, they allow researchers to investigate the underlying principles under highly controlled conditions.
What are the limitations?
Despite its significance, the experiment does not prove that time is an illusion or that clocks are unnecessary.
The miniature universe is an analog model rather than a complete representation of our cosmos.
Several important questions remain unanswered, including:
- Whether the same mechanism applies to the entire universe.
- How emergent time relates to gravity.
- Whether larger and more complex quantum systems behave similarly.
- How different theories of quantum gravity compare using similar experiments.
The findings should therefore be viewed as an important proof of concept rather than a definitive explanation of the nature of time.
The bigger picture
The University of Birmingham experiment represents an important milestone in experimental quantum physics.
For decades, questions about whether time is fundamental or emergent have largely remained philosophical or mathematical. By creating a miniature quantum universe in the laboratory, researchers have demonstrated that these ideas can now be explored experimentally.
If future studies confirm and expand on these findings, they could reshape how scientists think about one of the most familiar yet mysterious aspects of reality.
Time may not simply be something that exists independently of the universe. Instead, it could be something the universe continuously creates through change itself.
Key takeaways
- Researchers created a miniature quantum “universe” using 24,000 ultracold atoms.
- The experiment showed that a measurable form of time emerged without an external clock.
- Time was defined by changes in entropy inside the isolated quantum system.
- The findings support theoretical ideas that time may emerge from internal relationships rather than existing as a fundamental background property.
- The research could provide a new experimental platform for studying quantum gravity, cosmology, and the origins of spacetime.
