This Physicist’s 24,000-Atom Experiment Suggests Time Isn’t Real

Physicist Giovanni Barontini set out to solve a question that has puzzled physicists for decades: does time actually exist, or is it something that emerges from within the universe itself? His experiment, published June 11 in Physical Review Research, points to the latter.

The problem comes from the Wheeler-DeWitt equation, a key equation in quantum gravity — the field attempting to unify Einstein’s theory of gravity with quantum mechanics — which describes the universe as a whole system with no external time parameter. There’s no clock outside the universe keeping track. Barontini, based at the University of Birmingham, hypothesised that time instead arises from how things inside the universe interact.

To test it, he built a miniature ‘universe’ in his lab using a Bose-Einstein condensate, formed by cooling roughly 24,000 atoms to near absolute zero, where they behave as a single quantum entity. He trapped the condensate, split it with a thin sheet of laser light, and observed only one half — the ‘bright sector’ — while deliberately ignoring the other.

Atoms drifted back and forth across the divide, sometimes spilling over entirely. Barontini called the moment they flooded the observed half the ‘Big Bang,’ and the moment they flowed back the ‘Big Crunch.’ Rather than track time with an external clock, he devised an ‘entropic time’ based on the disorder flowing between the two halves — and it alone was enough to order the sequence of events.

The results were striking: time sped up, slowed down, and even stopped, tracking directly with how fast the atoms moved. ‘Time was speeding up or slowing down, or even stopping, depending on what the system was doing,’ Barontini told Live Science. He found that time’s forward direction and its very existence trace back to the same cause — an observer’s decision to ignore part of the system, with that ignorance generating the flow of time in the part left to observe.