What’s the time? - Marcus Brigstocke, Leon Lobo, Louise Devoy

“If you raise one of those clocks by a centimeter, you can measure that because the frequency changes, because it's sensitive to gravity being slightly different.” That is not a line from science fiction. It is a description of the next generation of optical atomic clocks, which are so precise they would lose or gain a second over the entire lifetime of the universe. This episode of The Infinite Monkey Cage, recorded at the Royal Observatory in Greenwich on its 350th anniversary, uses the milestone to explore why we need to know the time, how we have measured it, and what is at stake as our definition of the second is about to change again.

Why we need the time: from railways to finance

The obvious answer is that we need the time so we are not late. But the deeper answer, supplied by Leon Lobo of the National Physical Laboratory, is that nearly everything in modern digital infrastructure depends on time for synchronization. Telecom networks, satellite navigation, energy grids, and financial trading systems all require timing at the microsecond level or better. The historical trigger for standardizing time across a whole country was the railway. In 1847, British railway companies adopted Greenwich Mean Time across the entire network because local times based on different railway terminus clocks varied by up to thirty minutes, making connections impossible. By 1852, the obs