In 1956, David Pines formulated a phantom. He predicted the existence of seas of electric ripples that could neutralize each other, rendering the overall ocean motionless even as individual waves ebbed and flowed. The oddity, which came to be known as Pines’ demon, would be electrically neutral, and therefore invisible to light — the definition of tough to detect.

Over the decades, physicists managed to catch glimpses of demon variants. But Pines’ original demon — which would arise naturally out of electrons in metallic blocks — went undetected.

Now a team of physicists at the University of Illinois, Urbana-Champaign appears to have spotted Pines’ demon. After refining a technique for precisely tracking electrons as they ricochet off a material, the team produced and detected a series of periodic waves rippling through swarms of electrons. These waves, which physicists call “modes,” largely match Pines’ calculations. The researchers detailed their findings in Nature in August.

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