Physicists have coaxed particles of light into undergoing opposite transformations simultaneously, like a human turning into a werewolf as the werewolf turns into a human. In carefully engineered circuits, the photons act as if time were flowing in a quantum combination of forward and backward.

“For the first time ever, we kind of have a time-traveling machine going in both directions,” said Sonja Franke-Arnold, a quantum physicist at the University of Glasgow in Scotland who was not involved in the research.

Regrettably for science fiction fans, the devices have nothing in common with a 1982 DeLorean. Throughout the experiments, which were conducted by two independent teams in China and Austria, laboratory clocks continued to tick steadily forward. Only the photons flitting through the circuitry experienced temporal shenanigans. And even for the photons, researchers debate whether the flipping of time’s arrow is real or simulated.

Either way, the perplexing phenomenon could lead to new kinds of quantum technology.

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