A quote often mistakenly attributed to Albert Einstein, but actually attributed to science fiction writer Ray Cummings—“Time is what stops everything from happening at once”—is still considered the most succinct summary of one of the most fundamental properties of the universe. For Newton, time passes uniformly outside the material world; while Einstein's theory of relativity shows that time is inseparable from space and will expand and contract under the action of acceleration and gravity.After these two theories, a key question remains unanswered: What is it that prevents everything from happening at the same time?

To this end, Giovanni Barontini, a physicist at the University of Birmingham in the UK, chose to "go back to the starting point" and "create" a brand new micro-universe in the laboratory to observe how time was "born" from scratch. The universe he constructed is of course much simpler than the one we live in, consisting of only about 24,000 rubidium atoms. The atoms were cooled to extremely low temperatures, close to absolute zero, and were forced to share the same quantum state, forming what's known as a Bose-Einstein condensate. Subsequently, this condensed matter was artificially divided into two parts: one part could be directly measured by instruments, and the other part remained "dark" and isolated from external observations.

In this system, the research team allowed the "isolated universe" to undergo an expansion-like evolution, and at the same time allowed quantum waves to shuttle back and forth between the two "sub-universes". Through this process, Barontini obtained an experimental model that was sufficiently analogous to the real universe to test a controversial but attractive theoretical framework. This model corresponds to the so-called "Wheeler-DeWitt framework" in physics, which attempts to mathematically unify general relativity and quantum mechanics, treating everything as part of the overall wave function - including not only matter and space, but also time itself.

In traditional experience, we are accustomed to treating time as an external "clock", as if all events in the universe line up to occur on the scale of this clock. Barontini's experiment provides another perspective: time can be completely defined by changes within a closed system, without any external clock. In a note published by the University of Birmingham, he noted that this research is the first to demonstrate in a controlled experiment that "time" can be understood as a product of changes in the internal state of a system, rather than as an independent quantity that we imagine is ticking externally. This perspective provides new evidence for the nature of time in quantum gravity theory, suggesting that in some cases, using "internal time" to describe system evolution may be as valid as traditional "external time".

Under the Wheeler–DeWitt framework, “before” and “after” are no longer absolute time labels, but attributes that emerge naturally from the evolution of the degree of disorder within the system. In this experiment, this disorder - known as entropy - can be seen as a mathematical description of the gradual "loss" of quantum information as the universe expands. By repeatedly measuring the characteristics of this "mini-universe" of cold rubidium atoms as it expanded and contracted, Barontini was able to establish an orderly "sequence of events" for these changes. This sequence shows a direction similar to the "time" in our intuition: it flows in one direction along the direction of entropy increase, and will "get faster" or "slower" with the rate of entropy change.

Current cosmological models still have serious gaps in describing the relationship between macroscopic gravity and the microscopic quantum world, leaving us with almost no understanding of the true mechanisms inside a black hole or the details of the first moments of the Big Bang. The "miniature universe" built by Barontini's team provides researchers with an unprecedented experimental platform, allowing them to directly explore the behavior of "time" in the quantum gravity framework in a controlled environment. Mini-universe experiments like this are expected to gradually reveal why time appears in a single direction in an expanding universe, and why we have no reason to worry that "everything has already happened."

The relevant results have been published in the journal "Physical Review Research", with the University of Birmingham as the main publishing unit, and the research content has also been fact-checked by independent scientific editors. This work not only provides experimental support for philosophical debates about the nature of time, but also provides a new way of thinking for the future construction of a unified quantum gravity theory, understanding of the origin of the universe and extreme astrophysical phenomena.

learn more:

https://www.birmingham.ac.uk/news/2026/scientist-creates-miniuniverse-to-measure-time-without-a-clock

https://journals.aps.org/prresearch/abstract/10.1103/1h9j-df4k