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It took two major expeditions charting the solar eclipse of 1919 to verify Albert Einstein’s weird prediction about gravity — that it distorts the path of light waves around stars and other astronomical bodies, distorting objects in the background. Now, researchers have created the first precise analogue of that effect on a microchip.

Any large mass distorts the geometry of space around it, for instance making parallel light rays diverge or converge. One consequence, described by Einstein’s general theory of relativity, is that objects behind a body such as the Sun may look magnified or distorted as the optical path of light goes through the region of warped space.

Metamaterials scientist Hui Liu of Nanjing University in China and his colleagues mimicked this ‘gravitational lensing’ — which affects light in the vacuum of space — by making light travel through solid materials instead. Different transparent media have different indexes of refraction, causing light to bend. One example is at the interface between water and air, a familiar effect that makes a pencil look broken when it is half-dipped in water. But if a medium has an index of refraction that varies gradually rather than abruptly, it will make the the paths of light rays curve as they travel through it.

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space time

The warping of the empty space around a massive star means that the shortest path of light around a star is a ‘curved’ one — but the bending of light rays in a medium can mimic the same effect. | Nature Photonics
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