Physicists created a tiny universe where time emerged without a clock

A physicist in England has built a stripped-down laboratory stand-in for the cosmos that may bring researchers closer to settling one of physics' oldest riddles: what time actually is. Using a cloud of 24,000 atoms chilled to near absolute zero, the experiment showed that the steady march of time can emerge on its own from the internal shifts of a quantum system, with no external clock required to set the pace.

The work, led by Professor Giovanni Barontini of the University of Birmingham and published in the journal Physical Review Research, demonstrates that the passage of time can be tracked without ever consulting a timepiece. Instead of measuring change against a fixed external reference, the setup lets time reveal itself through the way the quantum system evolves internally, treating time as a byproduct of the system's own dynamics rather than an outside yardstick.

The question of whether time is a fundamental ingredient of reality or something that simply appears under the right conditions has occupied theoretical physicists for decades. Some frameworks in modern physics argue that the universe, taken as a whole, has no built-in clock at all. The Wheeler-DeWitt equation is a prominent example: it treats the entire universe as one single quantum state, with nothing outside it to tick off the seconds.

Under that kind of description, the particles making up the system behave simultaneously like discrete objects and like spread-out waves, a hallmark of quantum theory. Because there is no external observer or clock in this picture, any sense of "before" and "after" has to come from how different parts of the system relate to one another, rather than from a ticking mechanism running independently in the background.

Barontini's ultracold atom cloud effectively serves as a miniature, controllable version of that idea. By engineering the atoms into a shared quantum state and watching how their internal configuration shifted, the experiment produced a measurable stand-in for time's flow that depended entirely on the system's own behavior. That gives physicists a rare experimental foothold for a concept that has largely lived in equations and thought experiments rather than in the lab.

The implications reach beyond a single physics paper. Reconciling quantum mechanics with gravity has long been hampered by disagreements over how time should even be defined in a unified theory, a puzzle often called the "problem of time" in attempts to build a quantum description of gravity and cosmology. A working, testable model of clockless, emergent time could give theorists studying the universe's earliest moments a way to check their mathematics against something observable.

Caution is warranted, however. A cloud of tens of thousands of atoms in a Birmingham lab is a vastly simplified analogy for the universe as a whole, and the Wheeler-DeWitt framework it draws on remains one of several competing approaches to quantum gravity, not a settled consensus. Researchers will likely look to refine the experiment, probe how far the emergent-time behavior extends under different conditions, and see whether similar effects turn up in other quantum platforms before drawing broader conclusions about the nature of time itself.

Source: ScienceDaily