Tweezers made of light could illuminate the quantum twin paradox

The way gravity affects the quantum realm has so far remained mysterious. But an experiment that uses lasers as a pair of tweezers could let researchers assess how Earth’s gravitational pull affects an atom that ticks like a clock.

At extremely cold temperatures – think billionths of a degree above absolute zero – quantum effects make atoms behave like “matter waves” rather than particles. Physicists have long taken advantage of this: by colliding different matter waves and measuring the resulting ripples, they can identify the forces…