Physicists Create Miniature Universe Where Time Exists Without a Clock

In a recent study published in Physical Review Study, Professor Giovanni Barontini demonstrated that the passage of time can be measured without traditional clocks. This innovative experiment reveals that various forms of time can naturally emerge from the behavior of the quantum system itself.

Why Some Physicists Believe Time Is Not Fundamental

Several theories in modern physics propose that time may not be an intrinsic aspect of the universe. The Wheeler-DeWitt equation is one example, characterizing the universe as a singular quantum state devoid of an external clock. In this model, particles exhibit wave-like and particle-like behaviors, suggesting that the familiar flow of time arises from interactions within the system, rather than from independent ticking clocks.

To explore this concept experimentally, Professor Barontini created a simplified quantum “universe” using a cloud of 24,000 ultra-cold atoms, cooled to just a few billionths of a degree above absolute zero. This isolated system was separated by a thin barrier formed by two laser beams of varying frequencies, yielding two regions: one observed (“bright”) and the other not observed (“dark”).

A Miniature Universe with Its Own Sense of Time

Within this mini-universe, the bright regions expanded and contracted, mirroring a simplified version of the Big Bang followed by the Big Crunch—a scenario where the universe’s expansion eventually reverses.

Since the system was completely isolated, researchers reconstructed the sequence of events using solely the information from within the mini-universe, eliminating the need for an external laboratory clock.

The findings demonstrated that time does not exist as a constant backdrop; rather, it can emerge from changes occurring within quantum systems.

How Entropy Creates Time

This experiment highlighted that “time” arises from variations in disorder, or entropy, as atoms transition between bright and dark regions. Apart from this motion, the system remained isolated from external influences.

As the distribution of particles in the bright region increased or decreased, the system effectively moved forward in time. Once the particle distribution stabilized, the progression of time effectively halted.

Professor Barontini refers to this phenomenon as “entropic time.” In this format, time behaves as follows:

• Flows in a consistent direction, establishing a clear “arrow of time”
• Correctly orders events, regardless of whether the mini-universe expands or contracts
• Can vary in speed depending on how entropy is redistributed

Professor Barontini states: “In certain cosmological theories, particularly in quantum gravity, time does not manifest as a built-in feature. Yet, in everyday life, we perceive time as flowing from the past to the future. Why is this the case when most fundamental laws of physics are symmetrical in time?”

“This research provides the first controlled experimental evidence that ‘time’ can be defined by internal system changes, rather than relying on an external ‘ticking clock.’ This work enhances our understanding of the nature of time in quantum gravity and enables dynamic descriptions akin to classical time.”

Testing Quantum Gravity in the Laboratory

The researchers also found that a variant of the Schrödinger equation—central to quantum mechanics—can be represented using entropic time. This indicates that scientists can forecast how the “probability cloud” of a quantum system evolves over time, even when time is dictated by internal changes as opposed to an external clock.

This study addresses a persistent issue in physics: if a certain theory holds true and the universe lacks a built-in clock, how can events be accurately arranged? The experiment suggests that the answer lies in the internal evolution of the system itself.

Professor Barontini has shown that while the miniature universe adheres to conventional laws of quantum mechanics, concepts regarding the nature of time—typically restricted to theories describing the entire universe—can now be tested under laboratory conditions.

Towards Experiments on the Big Bang and Black Holes

Mini-universes offer a powerful experimental platform for examining theories in quantum cosmology and quantum gravity. Rather than depending solely on mathematical models, scientists may conduct laboratory experiments to explore concepts linked to the early universe.

The research team asserts that this approach could eventually extend to more complex quantum systems, paving the way for experiments that investigate the physics of the Big Bang, black hole simulations, and alternate theories regarding the emergence of time itself.