A Physicist Made Time Stop in a Jar of Atoms. Kind Of: Milky Way News

EARTH, Laniakea Supercluster—Time sped up. Then it slowed down. Finally, briefly, it stopped. No clock was harmed in the making of this sentence.

That is not a magic trick, and it is not a metaphor. It is what happens when a physicist takes seriously a genuine embarrassment buried in modern physics: in quantum gravity's central equation, time doesn't exist. The universe, at its deepest level, looks frozen.

Yet here we all are, aging.

Giovanni Barontini thinks the fix might fit in a jar of atoms. The University of Birmingham physicist cooled 24,000 atoms to a few billionths of a degree above absolute zero and built a clock from their shifting disorder—one that sped up, slowed down, and even stopped. In a paper published June 11 in the peer-reviewed journal Physical Review Research, "Testing the problem of time with cold atoms," he argues time may be something a system does, not a stage it sits on.

To get there, he split his ultracold atomic cloud (a Bose-Einstein condensate, essentially a blob of atoms acting as one) into a "bright" region he could watch and a "dark" region he could not, with atoms free to slosh between them. The bright side repeatedly ballooned and recollapsed, a tabletop cartoon of a Big Bang and a Big Crunch, according to a University of Birmingham release.

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Instead of reading a clock on the wall, he measured the system's entropy (its running tally of disorder) and used that to put the events in order. Call it entropic time. In the paper, that clock runs fast when entropy is flowing, slows when a higher barrier chokes the exchange, and stops altogether when the system settles into a stationary state. The striking part: a standard quantum equation, rewritten to run on this internal clock instead of ordinary time, reproduced what the atoms actually did.

"This study provides the first controlled experimental evidence that 'time' can be defined by changes within a system rather than as the external 'ticking clock' we think of as time," Barontini said in the Birmingham release.

If it holds, the result drags an old philosophical hunch onto the lab bench: that time is not a river the universe floats down but a byproduct of the universe changing.

"In some theories of the universe, especially quantum gravity, time doesn't appear as a built-in feature," Barontini said.

"Yet in everyday life, time flows from past to future."

The caveats are load-bearing. Barontini did not create a universe, and he did not prove time is an illusion. He built an analogue, basically a controllable stand-in, for one contested idea, among several, about where time comes from. In the paper, he writes that the results "establish a controlled experimental setting in which relational-time constructions can be quantitatively tested."

Tested, not settled.

Still, there is something bracing about watching a centuries-old question get poured into a jar of atoms and shaken like a martini for James Bond.

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