In a groundbreaking experimental feat, physicists at the University of Birmingham have successfully engineered a ‘mini-universe’ that promises to revolutionize our understanding of one of the most elusive concepts in science: time. Professor Giovanni Barontini and his team have constructed a quantum system of ultracold rubidium atoms that defies the traditional notion of time as an external parameter, instead exhibiting an emergent flow of time intrinsic to the system itself. This meticulous study, published today in Physical Review Research, brings quantum cosmology from the abstract folds of theory into a tangible laboratory reality.
The essence of the experiment harks back to profound theoretical conundrums. Conventional physics treats time as an absolute backdrop—a universal clock relentlessly ticking forward. However, prominent quantum gravity frameworks, such as those derived from the Wheeler-DeWitt equation, challenge this assumption by modeling the universe as a timeless quantum state. In this view, all cosmic events exist as a static superposition without any inherent temporal change, posing the enigmatic question: if there’s no fundamental clock, how do we delineate ‘before’ and ‘after’?
Addressing this philosophical and scientific riddle, Professor Barontini’s approach involves cooling approximately 24,000 rubidium atoms to temperatures just a fraction above absolute zero, close to minus 273.15 degrees Celsius. At these ultracold temperatures, quantum phenomena dominate, allowing atoms to occupy the same quantum state collectively. The atoms were confined within an optical trap created by intersecting laser beams tuned to different frequencies, partitioning the system into distinguishable ‘bright’ and ‘dark’ sectors—zones subjected to observation and zones effectively isolated from external measurement, respectively.
What emerges from this delicate configuration is a dynamic mini cosmos wherein the ‘bright’ sector exhibits cyclical expansion and contraction phases, conceptually analogous to cosmological phenomena such as the Big Bang and the speculative Big Crunch. Crucially, time in this mini-universe is not read from any external chronometer but is inferred from the internal evolution of the system itself. This leads to a remarkable outcome: the arrow of time arises from the increasing or decreasing entropy—essentially the spreading or concentration—of atomic distributions across these internal regions, thus giving rise to what the research terms ‘entropic time.’
Entropic time is an innovative conceptualization wherein time is defined by the disorder within an isolated quantum system rather than an independent external parameter. The experiment compellingly demonstrates that when entropy changes—when particles migrate between the bright and dark sectors—the system’s state evolves, which is interpreted as time ‘flowing.’ Conversely, if the distribution remains static, this ‘mini-universe’ experiences a halt in temporal progression, effectively demonstrating time’s emergence as a relational property. This insight could fundamentally alter our view of temporal mechanics in quantum regimes.
A particularly striking feature of entropic time is that it possesses all the characteristics expected of temporal flow in a macroscopic universe. It advances in a consistent, unidirectional manner, establishing a quantum arrow of time. Moreover, the ordering of events within the system remains coherent even amid the cyclic expansion and contraction phases, ensuring that cause precedes effect despite the complexity of the system’s internal dynamics. The variability of entropy also allows this form of time to accelerate or decelerate, mimicking the potential non-uniform flow of time suggested by advanced theoretical models.
Professor Barontini elucidates the philosophical depth underlying his work by emphasizing the anomaly between the symmetric laws of physics and the observed asymmetry of time. Classical physical laws often operate equivalently forward and backward in time, yet we perceive time as an irreversible march from past to future. His research offers the first controlled, physical evidence revealing how time can be an emergent phenomenon arising from internal changes rather than an independently existing quantity, thus potentially reconciling the apparent paradox.
From a quantum mechanics standpoint, the study demonstrates the compatibility of Schrödinger’s equation with entropic time, meaning that traditional quantum evolution equations can be re-expressed using this emergent temporal framework. This adaptability suggests that quantum systems can be coherently described in terms of internal temporal evolution without referencing an external time parameter, a foundational step toward a quantum theory of gravity.
This innovative quantum system serves as a powerful experimental platform to probe problems traditionally confined to speculative cosmology and theoretical physics. For decades, the lack of an empirical testbed limited the examination of time’s nature at quantum scales. Now, with this mini-universe, researchers can simulate and study complex cosmological scenarios, including cyclic cosmic evolutions, within a controlled laboratory environment, opening new avenues for validating competing models of quantum gravity.
Furthermore, the experimental paradigm has vast potential for expansion. By scaling and complicating the quantum system, future investigations might simulate phenomena analogous to black holes or other exotic spacetime geometries. Such experiments could be instrumental in discerning how time emerges near spacetime singularities or in high curvature regimes, addressing longstanding mysteries about the ultimate fate and beginning of our own universe.
The implications of this research extend well beyond fundamental physics. Understanding time’s emergence could impact areas ranging from information theory, where entropy and time are closely intertwined, to quantum computing, where controlling decoherence and time evolution is critical. Additionally, the experimental methodologies developed here could inspire broader technological advancements in ultra-precise metrology and quantum control.
In summary, the University of Birmingham team’s achievement marks a paradigm shift, translating deep cosmological and philosophical questions into testable physics. Professor Giovanni Barontini’s mini-universe is a watershed demonstration that challenges longstanding assumptions about time, laying the groundwork for future explorations into the quantum fabric of reality. This pioneering study heralds a new era in which the mysterious flow of time, once deemed intangible, becomes experimentally accessible and understandable.
Subject of Research: Not applicable
Article Title: Testing the problem of time with cold atoms
News Publication Date: 11 June 2026
Web References:
University of Birmingham Press Release & Images
Physical Review Research Article
References:
Barontini, G. (2026). Testing the problem of time with cold atoms. Physical Review Research, DOI: 10.1103/1h9j-df4k
Image Credits: University of Birmingham
Keywords
Ultracold atoms, Quantum cosmology, Entropic time, Quantum gravity, Quantum mechanics, Time emergence, Wheeler-DeWitt equation, Mini universe, Quantum simulation, Schrödinger equation, Black hole simulation, Big Bang theory
