A new quantum experiment suggests that time might not be a basic part of the universe. Instead, it could arise from how things change inside a system. This experiment offers new insights into one of physics' biggest mysteries.
A scientist at the University of Birmingham created a "mini universe" using ultracold atoms. This setup helped show that time can emerge from changes in entropy within a system.
A Universe Without a Clock
Some physics theories, like the Wheeler–DeWitt equation, suggest that time isn't a fundamental property. They propose the universe might exist as a single quantum state that doesn't change. In this view, there's no external clock. Our experience of time comes from how different parts of the system relate to each other.
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Start Your News DetoxProfessor Giovanni Barontini explored this idea. He built a sealed quantum system with 24,000 ultracold atoms. These atoms were cooled to just a few billionths of a degree above absolute zero.
He trapped the atoms and separated them with a thin barrier made of two laser beams. This created a "bright" region that was observed and a "dark" region that was not.
The bright region repeatedly expanded and contracted. This was similar to a Big Bang followed by a Big Crunch. The experiment showed that the sequence of events could be understood from inside the system. No external clock was needed.
The results suggest that time can come from changes within a quantum system. It doesn't have to be an independent, external feature.
Entropic Time and the Arrow of Time
The mini universe also showed that time can come from entropy. Entropy is the spread or disorder of particles within a system. Atoms could move between the bright and dark regions while the system stayed isolated.
As atoms moved, the distribution of particles changed. When this distribution increased or decreased, the system moved forward in time. If the distribution stayed the same, time effectively stopped.
Barontini calls this "entropic time." It flows in one direction, creating a clear "arrow of time." It also correctly orders events, even in a system that expands and contracts. Entropic time speeds up or slows down depending on how entropy is redistributed.
Professor Barontini explained that in some theories, like quantum gravity, time isn't a built-in feature. Yet, in daily life, time moves from past to future. This study offers the first experimental proof that time can be defined by changes within a system. It's not just an external "ticking clock."
The study also showed that a version of the Schrödinger equation, a key equation in quantum mechanics, can use entropic time. This helps researchers predict how a quantum system's "probability cloud" changes over time.
This research helps answer a long-standing question in physics. If some theories have no built-in clock, how can events be ordered without an external measure of time? Barontini's work shows that such a system still follows quantum physics laws. This means questions about the nature of time, once only theoretical, can now be studied in labs.
This experiment offers a valuable way to test ideas in quantum cosmology and gravity. It allows scientists to study concepts related to the early universe in a controlled setting. The method could eventually be used for more complex systems. This could help scientists study the physics of both the Big Bang and the Big Crunch. It might also help simulate black holes and test theories about how time emerges in the universe.
Deep Dive & References
Testing the problem of time with cold atoms - Physical Review Research, 2026
