Inside the incredibly slow race to reinvent time

The latest atomic clocks are so staggeringly precise that they are going to redefine the second. The only question now is when

Physics

19 August 2020

By Rachel Nuwer

ANDREW LUDLOW’S is no ordinary ticker. An intricate tangle of tubes, cables and lasers occupying an entire room at his lab in Boulder, Colorado, it is one of the best timekeeping devices ever made. “It’s the Lamborghini of atomic clocks,” he says.

That isn’t to say it is fast. But Yb-2, as the clock is known, is precision engineered. In fact, it should measure out each passing second so precisely that it wouldn’t miss a beat for around 20 billion years – more than the age of the universe.

This is the stunning frontier of precision at which timekeeping now finds itself. Clocks such as Ludlow’s could spur on as yet unheard-of technological innovations. They could transform our understanding of the universe, revealing wrinkles in established laws of physics and variations in the fundamental constants of nature that would otherwise be impossible to detect. But for metrologists like Ludlow, they raise an even more fundamental question: is it time once again to redefine time?

That might like seem an odd thing to consider for what is a fundamental property of the universe. The flow of time is an enigma; many physicists even suggest it is just an illusion. But clock time is our own invention. We define its basic units – the hours, minutes and seconds that break up the day. They started out as subdivisions of the time it takes Earth to rotate around its axis. Indeed, when astronomer Christiaan Huygens invented the pendulum clock in the 17th century, a second became firmly established as 1/86,400 of a solar day, a factor derived from the division of the …