24,000 Atoms Build ‘Mini-Universe’ to Measure Time Without Clocks
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A system built from 24,000 ultracold atoms is challenging fundamental assumptions about the nature of time, according to new research from the University of Birmingham.
Professor Giovanni Barontini and colleagues constructed the quantum system, cooled to just a few billionths of a degree above absolute zero, to mimic the expansion and collapse of a cosmos, creating a “bright” and “dark” region with laser beams. The experiment demonstrated the ability to measure the flow of time within the system itself, without relying on an external laboratory clock, revealing that “time” can be defined by changes within a system rather than as the external ‘ticking clock’ we think of as time, as Professor Barontini explains. This innovative approach offers new insight into quantum gravity and provides a powerful testbed for theories relating to the early universe.
Ultracold Rubidium Atoms Model ‘Mini Universe’ Researchers at the University of Birmingham have constructed a unique experimental system utilizing 24,000 ultracold rubidium atoms to model the fundamental nature of time itself, moving beyond reliance on conventional laboratory clocks for measurement. This was created by trapping the particles and dividing them with two laser beams of differing frequencies, establishing a visually distinct “bright” and “dark” region within the atomic cloud. The experiment deliberately induced expansion and collapse within the bright sector, simulating a “Big Bang and a Big Crunch” scenario to observe the behavior of time within this contained environment. Crucially, the sequence of events was reconstructed from within the mini-universe, eliminating the need for an external time reference; researchers observed that time progressed as the disorder, or entropy, of the atoms increased or decreased. Atoms were permitted to move between the ‘bright’ and ‘dark’ regions, but the system remained isolated, allowing for a controlled observation of temporal dynamics.
Professor Giovanni Barontini described this observed phenomenon, noting that it “correctly orders events, even in a system expanding and contracting like a mini cosmos.” This approach challenges established theories suggesting the universe lacks inherent time, instead positing that time arises from internal relationships between particles. “In some theories of the universe, especially quantum gravity, time doesn’t appear as a built-in feature,” explained Professor Barontini. “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?” The team successfully demonstrated that the standard equations of quantum mechanics, including the Schrödinger equation, remain valid when utilizing entropic time, opening avenues for testing complex cosmological theories within a laboratory setting. 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?
Entropic Time Emerges From Atomic Disorder The core of the experiment lies in demonstrating that the flow of time can be measured within the system, independent of an external clock. Specifically, when the spread of particles in the bright sector increased or decreased, time appeared to advance; when the distribution stabilized, time, in effect, halted. This concept challenges long-held assumptions about the nature of time, particularly within theories of quantum gravity.
The team also showed that the standard Schrödinger equation of quantum mechanics remains valid when using entropic time, allowing for predictions about the evolution of quantum states. The implications extend beyond fundamental physics, potentially offering a pathway to simulate extreme phenomena like black holes and probe the earliest moments of the universe within a laboratory setting. Schrödinger Equation Validated Using ‘Entropic Time’ The core innovation lies in the ability to discern the passage of time by observing changes in the distribution of atoms within the ‘bright’ sector, a phenomenon Barontini terms ‘entropic time’. When the spread of particles increased or decreased as atoms moved between regions, the system registered forward movement in time; conversely, a static distribution signified temporal stasis. This observation is significant because it demonstrates that time can be defined by internal changes, specifically, the disorder or entropy of the atomic cloud, rather than an external, universally ticking clock. Crucially, the experiment confirms that the fundamental equation governing quantum mechanics, the Schrödinger equation, remains valid even when time is defined through entropy, allowing for accurate predictions of how quantum systems evolve. This validation addresses a long-standing question in theoretical physics: if some models propose the absence of inherent time in the universe, how can the sequence of events be determined? Barontini’s work suggests that the universe’s dynamics can be described just as effectively using this entropic time as with conventional time, opening avenues for testing theories about the early universe, black holes, and quantum gravity within a controlled laboratory setting. 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. Source: https://www.birmingham.ac.uk/news/2026/scientist-creates-miniuniverse-to-measure-time-without-a-clock Stay current. See today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: