Scientists built a tiny quantum universe where time appeared to emerge all by itself.
- Date:
- July 9, 2026
- Source:
- University of Birmingham
- Summary:
- What if time doesn't actually exist until something changes? Scientists at the University of Birmingham created a tiny "mini universe" using 24,000 ultracold atoms and showed that the flow of time can emerge naturally from changes inside a quantum system, without relying on any external clock.
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A physicist at the University of Birmingham has created a laboratory "mini universe" that brings scientists a step closer to answering one of the biggest questions in physics: What is time?
In a study published in Physical Review Research, Professor Giovanni Barontini demonstrates that it is possible to measure the passage of time without relying on a clock. Instead, the experiment shows that a version of time can emerge naturally from the behavior of a quantum system itself.
Why Some Physicists Think Time May Not Be Fundamental
Several theories of modern physics suggest that time may not exist as a built in feature of the universe. One example is the Wheeler-DeWitt equation, which describes the universe as a single quantum state with no external clock. In this picture, particles display both wave like and particle like behavior, and the familiar flow of time must arise from relationships between different parts of the system rather than from an independent ticking clock.
To investigate this idea experimentally, Professor Barontini created a simplified quantum "universe" using a cloud of 24,000 ultracold atoms cooled to just a few billionths of a degree above absolute zero. The atoms were sealed inside an isolated system and separated by a thin barrier created with two laser beams of different frequencies. This produced two regions: an observed ("bright") region and an unobserved ("dark") region.
A Tiny Universe With Its Own Sense of Time
Inside this miniature universe, the bright region repeatedly expanded and contracted, resembling a simplified version of a Big Bang followed by a Big Crunch, a hypothetical event in which the expansion of the universe eventually reverses.
Because the system was completely isolated, researchers could reconstruct the sequence of events using only information from inside the mini universe itself, without referring to any outside laboratory clock.
The results showed that time could emerge from changes taking place within the quantum system rather than existing as an independent background that always moves forward.
How Entropy Created Time
The experiment revealed that "time" arose from changes in the disorder, or spread (entropy), of the atoms as they moved between the bright and dark regions. Aside from this movement, the system remained isolated from the outside world.
As the distribution of particles in the bright region increased or decreased, the system effectively moved forward in time. When the particle distribution stopped changing, time itself effectively came to a halt.
Professor Barontini refers to this concept as "entropic time." In the experiment, this form of time:
- Flows in one consistent direction, producing a clear "arrow of time"
- Correctly orders events, even as the mini universe expands and contracts
- Can speed up or slow down depending on how entropy is redistributed
Professor Barontini said: "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?
"This study provides the first controlled experimental evidence that 'time' can be defined by changes within a system rather than as the external 'ticking clock' we think of as time. It offers new insight into the nature of time in quantum gravity that could be used to describe dynamics just as effectively as conventional time."
Testing Quantum Gravity in the Laboratory
The researchers also found that a version of the Schrödinger equation, the fundamental equation of quantum mechanics, can be expressed using entropic time. This means scientists can still predict how the "probability cloud" of a quantum system evolves over time even when time is defined by internal changes rather than an external clock.
The work tackles a long standing problem in physics. If certain theories are correct and the universe has no built in clock, how can events be placed in the correct order? The experiment suggests that the answer may lie in the system's own internal evolution.
Professor Barontini showed that the miniature universe follows the standard laws of quantum mechanics while allowing ideas about the nature of time, which are normally confined to theories describing the entire universe, to be tested under controlled laboratory conditions.
Toward Experiments on the Big Bang and Black Holes
The mini universe provides a valuable experimental platform for testing ideas in quantum cosmology and quantum gravity. Instead of relying only on mathematical models, scientists may now be able to investigate concepts related to the early universe through laboratory experiments.
The team says the same approach could eventually be expanded to more complex quantum systems, opening the door to experiments that explore the physics of the Big Bang, the "Big Crunch," simulated black holes, and competing theories about how time itself emerges.
Story Source:
Materials provided by University of Birmingham. Note: Content may be edited for style and length.
Journal Reference:
- Giovanni Barontini. Testing the problem of time with cold atoms. Physical Review Research, 2026; 8 (2) DOI: 10.1103/1h9j-df4k
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Facts Only
* Physicists created a laboratory "mini universe" using 24,000 ultracold atoms.
* The experiment demonstrated that the flow of time can emerge naturally from changes within a quantum system without an external clock.
* Researchers used an isolated system divided into a bright and dark region.
* The bright region exhibited repeated expansion and contraction.
* Time was reconstructed using only information from inside the mini universe.
* "Time" arose from changes in the disorder, or spread (entropy), of the atoms moving between regions.
* Increased or decreased particle distribution in the bright region caused the system to move forward in time.
* A form of this time was termed "entropic time."
* Entropic time flows in one direction, creating an arrow of time and ordering events.
* The Schrödinger equation can be expressed using entropic time.
* The research was conducted at the University of Birmingham.
Executive Summary
Scientists at the University of Birmingham created a laboratory "mini universe" using 24,000 ultracold atoms to investigate the nature of time. The experiment demonstrated that the flow of time can emerge naturally from changes within a quantum system, independent of an external clock. Researchers observed a bright and dark region within this isolated quantum system, which behaved similarly to a cosmological expansion and contraction.
The study suggests that time is not necessarily a fundamental background but rather emerges from the behavior and changes—specifically entropy—within the quantum system itself. This concept is termed "entropic time," where the movement between regions of increased or decreased disorder dictates the progression of time. The research also showed that a version of the Schrödinger equation can be expressed using this entropic time, implying that internal changes can govern the evolution of quantum probability clouds.
The findings provide experimental evidence supporting theories from quantum gravity suggesting that time may arise from system dynamics rather than existing as an independent entity. Furthermore, the setup offers a platform to test concepts related to the Big Bang and black holes in controlled laboratory conditions by using complex quantum systems.
Full Take
The core implication of this work lies in decoupling the concept of temporal flow from a presumed external, absolute backdrop, aligning with frameworks like the Wheeler-DeWitt equation where time is emergent rather than fundamental. The emergence of "entropic time" suggests that the perceived unidirectional nature of time—the arrow of time—is intrinsically linked to the increase of entropy within an isolated system; this mirrors statistical mechanics on macroscopic scales. The fact that internal changes in particle distribution dictate temporal progression challenges the classical, Newtonian view where time is a universal constant ticking independently of physical reality.
This shifts the focus from searching for "what is time" in the universe as a fixed entity to understanding "how systems define their own evolution." If time is defined by entropy redistribution within a system, then the problem shifts from finding an external clock to rigorously defining the initial conditions and constraints of quantum gravity that govern this entropic emergence. The ability to express fundamental equations like the Schrödinger equation through this emergent time suggests a unified perspective where thermodynamics and quantum mechanics are intrinsically linked in defining temporal structure.
The experiment serves as a crucial bridge, moving concepts from highly abstract theories of quantum cosmology into experimentally testable laboratory dynamics. The next challenge involves rigorously connecting this internal entropic definition to broader cosmological models, specifically testing how the dynamics of a localized, isolated system scale up to describe phenomena like the Big Bang or black hole evaporation. What physical mechanism governs the transition from local entropic change to global cosmic time? How do we define the boundary conditions for an "entropic universe" when extrapolating these findings to cosmology?
Sentinel — Human
The text appears to be a well-researched piece of science reporting that effectively synthesizes complex quantum physics findings into an accessible narrative about the nature of time.