Light passing through ripples on a water surface paints dancing patterns on the bottom of a pool. Engineers have used a similar idea to make light compute. They fabricated a tiny plate with a wavy relief: each ridge and groove deflects rays in its own way. When an image falls on such a surface, the light transmitted through it converges at different points behind it. The brightness at each point is the answer: which digit or object was in the picture.

The plate measures 40 by 40 micrometers — several times smaller than the thickness of a human hair. It needs no wires, no transistors, and no software. The entire "program" is etched into the surface shape, just as a riverbed determines the path of water. Light of different colors is deflected at different angles, so the same chip can simultaneously handle up to 20 independent tasks: each on its own color, like musicians in an orchestra playing different parts.

This approach promises computers that consume almost no energy and operate at the speed of light. In the future, cameras and sensors might sort images right on the spot, without sending data to the cloud.