Physicists have built a miniature quantum universe using 24,000 ultracold atoms, demonstrating how time can emerge from changes within a system rather than from an external clock. Could this strange laboratory experiment offer clues about how our own universe works?
Imagine living in a universe where there are no clocks, no seconds, no minutes and no ticking mechanism marking the passage of time. Nothing outside the universe tells you whether one event happened before another. Yet things still change. Particles move, matter evolves and events unfold.
It sounds like an impossible situation. After all, how can anything happen without time?
This is precisely the kind of question that has troubled theoretical physicists for decades. And now, an experiment involving approximately 24,000 atoms cooled to temperatures just above absolute zero has brought scientists a little closer to investigating it.
Researchers at the University of Birmingham have created a laboratory system described as a miniature universe. Its behaviour offers experimental insight into an extraordinary possibility: time might not be a fundamental ingredient of reality. It could emerge from relationships and changes occurring within the universe itself.
The discovery does not mean scientists have recreated the Big Bang or built an actual universe. But it does provide a fascinating experimental window into one of physics’ deepest mysteries.
A Universe Without an External Clock
We tend to think of time as something that exists independently of everything around us.
A clock continues ticking whether the Earth rotates, a star explodes or a galaxy moves through space. In everyday physics, time is treated as a parameter that helps describe how events change.
But when physicists attempt to understand the entire universe using quantum mechanics and gravity, this familiar picture becomes complicated.
One of the major challenges is known as the problem of time.
In certain approaches to quantum gravity, particularly those associated with the Wheeler-DeWitt equation, the universe is described without an ordinary external time variable.
This creates a remarkable question. If the universe includes everything that exists, what would an external clock even be?
There is no second universe sitting outside ours to measure its progress.
One proposed answer is called relational time. Under this idea, time can emerge from relationships between different parts of a physical system. Instead of relying on an outside clock, one part of the system can effectively measure changes in another.
It is an intriguing theoretical possibility. But could physicists actually demonstrate something like this in a laboratory?
That was the challenge behind the Birmingham experiment.
How Scientists Built Their Miniature Universe
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Alt text: Scientists’ miniature quantum universe experiment using ultracold atoms to investigate how time emerges.
The experiment was led by Professor Giovanni Barontini at the University of Birmingham.
Rather than attempting to reproduce the enormous scale of the cosmos, researchers created a carefully controlled quantum system containing approximately 24,000 ultracold atoms.
The atoms were cooled to temperatures just a few billionths of a degree above absolute zero, allowing quantum behaviour to become especially important.
The researchers confined the atoms using a specialised experimental arrangement and divided the system into two regions using laser light.
One region was called the bright sector. The other was called the dark sector.
Atoms could move between these regions, allowing the researchers to study how the distribution of particles changed.
The bright sector repeatedly expanded and contracted, creating a simplified analogy with two hypothetical cosmological events: the Big Bang and the Big Crunch.
The resemblance was mathematical and conceptual, not literal. No actual cosmic explosion or gravitational collapse took place inside the laboratory.
What mattered was that researchers had created a system whose internal changes could be studied without depending on an external clock to define its evolution.
The experiment effectively provided a small, controllable testing ground for ideas normally discussed in theoretical cosmology.
The Strange Discovery: Time Emerged From Entropy
Here is where the experiment becomes particularly interesting.
Instead of measuring time using seconds, minutes or an external clock, Barontini used changes associated with entropy.
Entropy is a fundamental concept in thermodynamics. It describes how energy and physical states are distributed, and it plays a central role in understanding why many processes have a preferred direction.
Think about an ice cube melting inside a glass of water. The process naturally moves from a relatively ordered arrangement towards a more dispersed state. You do not normally see the water spontaneously gather itself back into the original ice cube.
This relationship between entropy and the direction of physical processes is connected to what scientists call the arrow of time.
In the miniature universe, researchers used the exchange of entropy between the bright and dark sectors to construct an internal measure of time.
As atoms moved between the regions, changes in their distribution provided a way to describe the progression of events.
The surprising result was that this internal measure could order events without relying on the laboratory’s external clock.
In other words, the system could use its own internal changes to establish a meaningful sequence of events.
The researchers also demonstrated that a version of the Schrödinger equation, a central equation of quantum mechanics, could be expressed using this entropic measure of time.
This was important because it suggested that the internal measure was not merely a convenient way of describing events. It could also be used to describe the evolution of the quantum system.
The findings were published in Physical Review Research.
Original research: Testing the problem of time with cold atoms – Physical Review Research.
What If Time Can Speed Up, Slow Down or Even Stop?
One of the most thought-provoking aspects of the experiment was how the internal measure of time behaved.
It did not necessarily advance at a constant rate.
Its progression depended on the exchange of entropy between the two regions. When entropy exchange changed, the rate of this internal time changed as well. When the relevant exchange ceased, this particular measure of time stopped advancing.
That does not mean the researchers stopped time itself. The laboratory continued operating, and the experiment remained subject to ordinary physical time.
Rather, the researchers showed that a system’s internal description of time can behave differently from the external clock used by scientists.
This distinction is crucial.
Imagine an isolated universe with no outside observer and no external clock. Its inhabitants could potentially understand the passage of time through changes happening within their own surroundings.
A star burns fuel. Planets move. Particles interact. Entropy changes.
These processes could provide the relationships needed to distinguish one moment from another.
Could something similar explain the time we experience in our own universe?
It is an idea worth investigating, although the laboratory experiment does not establish that this is exactly how cosmic time originates.
Could Our Entire Universe Work the Same Way?
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Alt text: Artistic scientific illustration of galaxies and cosmic structures representing the possible emergence of time within the universe.
This is where a small quantum experiment begins to raise enormous questions.
Our universe contains everything we know: galaxies, stars, planets, radiation, dark matter and the physical processes that govern their evolution.
But what if time is not an independent background against which all these events take place?
What if it is instead an emergent property of relationships between physical processes?
Under this possibility, time would not necessarily be something that exists separately from the universe. It could be a feature that arises from the way the universe evolves.
This is not an entirely new idea. Physicists have explored relational time and the problem of time in quantum gravity for decades.
The importance of Barontini’s work is that it brings some of these concepts into an experimentally controlled setting.
There is, however, a major limitation.
The miniature system is a simplified quantum model. It does not reproduce the full gravitational behaviour, enormous complexity or cosmological history of our universe.
Scientists cannot conclude from this experiment that the Big Bang generated time through precisely the same mechanism.
What it offers is a way to test aspects of theories that previously existed largely in mathematical descriptions.
Does This Mean Time Is an Illusion?
Not necessarily.
If time can emerge from physical relationships, that does not mean the passage of time is imaginary.
Consider temperature. Individual atoms do not possess temperature in exactly the same way that a large collection of atoms does. Temperature emerges as a collective property of many particles.
Similarly, some physicists investigate whether time could emerge from the collective behaviour and relationships of more fundamental physical elements.
An emergent property can be entirely real, even if it is not fundamental.
A useful distinction is that the experiment investigates how time can be defined and measured inside a quantum system. It does not demonstrate that clocks are meaningless, that time does not exist or that humans can escape the effects of ageing.
Our everyday experience of time remains consistent with the physical theories used to describe the world around us.
The deeper question is whether that familiar experience has an even more fundamental explanation.
Could This Experiment Help Scientists Understand the Big Bang?
The early universe presents physicists with some of the most difficult problems in modern science.
During its earliest stages, the universe was extraordinarily hot and dense. Understanding those conditions requires theories that can account for both quantum physics and gravity.
Unfortunately, scientists cannot recreate the entire early universe in a laboratory.
But they can construct smaller physical systems that reproduce selected mathematical features of complicated cosmological models.
This is the broader significance of quantum simulations.
The Birmingham experiment demonstrates how researchers can investigate questions about time using ultracold atoms and controlled quantum interactions.
Future research could explore more complicated systems, including models inspired by the early universe, gravitational phenomena and hypothetical cosmic expansion and contraction.
These experiments may eventually help physicists understand which mathematical descriptions of time are physically meaningful.
There is also a connection to the hypothetical Big Crunch, a scenario in which cosmic expansion eventually reverses and the universe collapses.
The experiment’s expanding and contracting regions provide a simplified model for investigating related dynamics. They do not predict that our universe will end in a Big Crunch.
Current observations indicate that cosmic expansion is accelerating, making the ultimate fate of the universe an active area of cosmological research.
What Scientists Still Do Not Know
Despite the excitement surrounding the discovery, several enormous questions remain unanswered.
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Is time fundamentally real, or does it emerge from quantum relationships?
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Could the arrow of time be explained entirely through entropy?
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Does gravity play a role in creating the experience of time?
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Could the earliest moments of the universe be described without assuming that time already existed?
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Would a more complicated quantum system reveal additional properties of emergent time?
These are not questions that one experiment can settle.
The research provides a new experimental approach, but connecting its findings to the actual universe will require further theoretical development and increasingly sophisticated experiments.
For now, physicists have demonstrated that a controlled quantum system can have an internal measure of time without depending on an external clock.
That is already a remarkable result.
Further reading and scientific sources:
The Universe May Be More Mysterious Than We Imagined
For centuries, humans have measured time through the movement of the Sun, the rotation of the Earth and increasingly sophisticated clocks.
We have built satellites that depend on extraordinarily precise timekeeping. We measure the ages of stars, calculate the movement of galaxies and reconstruct the history of the cosmos.
Yet the fundamental nature of time remains one of the hardest problems in physics.
The miniature universe created by Giovanni Barontini and his team offers an intriguing possibility: perhaps time does not need an external clock to exist as a meaningful physical quantity.
Perhaps it can emerge from the relationships between things happening inside a system.
And if this principle eventually proves relevant to the universe as a whole, our understanding of reality could change in profound ways.
The experiment did not create another universe. It did something arguably more interesting: it allowed scientists to investigate how a universe might keep track of its own existence.
