(koto_feja/Getty Images) A breakthrough in chronometry decades in the making could redefine the limits of how we keep time.

Most clocks, from wristwatches to the systems that run GPS and the internet, work by tracking regular, repeating motions. To build a clock, you need something that ticks in a perfectly repeatable way.

For many years, cesium atomic clocks have been reliably keeping time around the world. But the future belongs to even more accurate clocks: optical atomic clocks. In a few years' time, they could ...

Time feels familiar. It marks every moment of daily life, from the ticking of a wall clock to the changing numbers on a smartphone screen. Yet despite its constant presence, time remains one of the ...