A grandfather clock uses a pendulum to keep time, a swinging weight that oscillates back and forth at fixed intervals.
However, if the pendulum swings once every second, a tiny error quickly spirals into a major timekeeping problem. The solution is to break the second down even further and to use a ‘pendulum’ that swings much faster.
Atomic clocks, developed in the Fifties, are based on this principle. Instead of a swinging pendulum, these devices use the oscillations of caesium atoms as they jump between energy states when exposed to microwave radiation. In a single second, a caesium atom oscillates an incredible 9,192,631,770 times.
Optical lattice clocks take this idea one step further still. Instead of exciting atoms with microwaves, laser beams are used. These oscillate much more rapidly, splitting the second into even more fragments, and thus enabling more precise measurement.
Strontium atoms are cooled by lasers until they move no faster than a few centimeters every second. The laser beam creates a pattern similar in shape to an egg box, which traps the individual atoms in a regular lattice, allowing their atomic ‘tick’ to be measured. From 1000 CE and right up until the Sixties, a second was defined, much as you might expect, as 1/86,400 of the average solar day – ie 60 seconds in every minute, 60 minutes in every hour, 24 hours in every day. However, given that the Earth wobbles on its axis and our orbit around the Sun is not consistent, a more accurate means of measuring time was required.
The atomic clock enabled us to measure time much more precisely, defining one second as the time it takes a caesium atom to cycle between two energy states exactly 9,192,631,770 times.