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.
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