Quartz crystal, a tiny musical tuning fork of high frequency and stability, is used in most modern clocks. The atomic clock, which all our normal clocks check to discipline themselves, was first built by Louis Essen. It worked by calculating the flipping frequency of electrons in caesium atoms. The frequency is so sharp that one second is exactly 9,192,631,770 caesium electron spin flips.

GPS technology, something found on every smartphone, has the accuracy of atomic clocks built-in.

We usually check the time using smartwatches and smartphones, which have clocks tallying the time with signals from atomic clocks, some of which are installed on GPS satellites.

The signals from atomic clocks are now becoming increasingly accurate, allowing us to measure gravity waves in ...