Physicists confirm 'negative time' is real by asking the atoms themselves [View all]

[Judi Lynn]

A new experiment confirms that photons passing through a cloud of atoms can spend a negative amount of time there, and the atoms themselves are the ones saying so.

By Larissa G. Capella
published 20 May 2026



An illustration of light being absorbed by an atom. New experiments confirm that some photons can spend a negative amount of time within a cloud of atoms, reaching their destination before they technically enter the cloud.
(Image credit: koto_feja via Getty Images)



When a beam of light passes through a cloud of atoms, photons (particles of light) sometimes appear to spend a negative amount of time there, with light seeming to exit the cloud before it even enters. Now, physicists have confirmed this quantum quirk by asking the atoms themselves.

"This doesn't mean that we're on the verge of building a time machine or anything like that," study co-author Howard Wiseman, a theoretical quantum physicist at Griffith University in Australia, told Live Science. "It can all be understood with standard physics, but it's yet one more weird property of quantum physics that people hadn't suspected."

Photons that pass through an atomic cloud can be temporarily absorbed. They vanish as particles of light and reappear as atomic excitations — a kind of stored energy — before being reemitted. Some photons, called transmitted photons, make it through in roughly the same direction they entered Others scatter off in random directions.

Experiments dating back to 1993 had already hinted that transmitted photons tend to arrive at a detector before the center of their own pulse even enters the cloud. That implies a negative transit time.

More:
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