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 ...

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.