×îÐÂÂé¶¹ÊÓÆµ

Technology

The epic quest to redefine the second using the world's best clocks

A more precise definition of the second is crucial to all sorts of physical measurements – but to get there, scientists have to pack up their extraordinarily fragile optical clocks and take them on tour

By Karmela Padavic-Callaghan

2 April 2025

×îÐÂÂé¶¹ÊÓÆµ. Science news and long reads from expert journalists, covering developments in science, technology, health and the environment on the website and the magazine.

Roberto Cigna

On a large table draped with hundreds of cables, a maze of mirrors and lenses bounces and guides a thin beam of laser light. It culminates at a silvery capsule, which holds 40,000 strontium atoms cooled to within a whisker of absolute zero. This delicate edifice is an optical clock, one of the world’s most accurate timepieces.

Instruments like this aren’t exactly designed to be portable – which makes it more than a little surprising that the operators of one such device at the German national metrology institute packed it into a trailer and sent it hurtling down a motorway. It was the start of…

Sign up to our weekly newsletter

Receive a weekly dose of discovery in your inbox! We'll also keep you up to date with ×îÐÂÂé¶¹ÊÓÆµ events and special offers.

Sign up

To continue reading, today with our introductory offers

or

Existing subscribers

Sign in to your account
Piano Exit Overlay Banner Mobile Piano Exit Overlay Banner Desktop