Atomic Clocks

When Time Matters

We live in a fast paced world. Technologies such as mobile phones, satellite navigation and the internet have changed the way we live out our lives. And yet much of the modern digital age owes itself to an often misunderstood and underrated technology – the atomic clock.

Atomic clocks are incredibly accurate. In comparison to electronic clocks, which may drift by a second each week, atomic clocks neither lose nor gain a second in thousands of years and to discover the key to this incredible accuracy of these clocks, you have to look at what makes them tick.

Mechanical clocks keep time using pendulums and springs whilst electronic clocks and watches use the frequency generated by a current being passed through a crystal, usually quartz, in a method known as oscillation. And atomic clocks use a similar method of oscillation to keep time, but rather than using a crystal, as their name suggests atomic clocks rely on atoms.

Atomic – but not radioactive!

Atomic clocks were invented in the 1950’s. They are not radioactive as they do not use radiation from decaying atoms, instead atomic clocks use the precise frequency emitted by atoms when they change energy states. This frequency, or ticking, of the most commonly used atom in atomic clock – caesium 133, accounts for 9,192,631,770 cycles of radiation every single second.

And this frequency never alters and because of the high number of ticks each second it provides a really accurate base for measuring time, so-much-so that the International System of Units (SI) now defines the official second as this many cycles of the caesium 133 atom.

The development of atomic clocks has continued through the decades and huge steps have been made in precision over the last few years. Atomic clocks are becoming increasingly more accurate, they also form the basis of the world’s global timescale – UTC (Coordinated Universal Time).

Coordinated Time

The use of atomic clocks is widespread and they form the basis for many modern technologies and applications: GPS (Global Positioning System), air traffic control, the stock exchange and even the internet, all rely on the accuracy of atomic clocks.

But these time keeping devices are not practical consumer items. They often use technologies such as lasers and liquid nitrogen and so are often only located in large scale laboratories and universities.

However, it is possible to use the ultra precise time from an atomic clock as organisations like NIST in North America (National Institute of Standards and Time) and the UK’s National Physical Laboratory (NPL), broadcast the time from their atomic clocks via long wave radio. These signals can be picked up by radio clocks that can be synchronised to the time signal.

Network time servers can also receive these time signals and use them to synchronise computer networks using the Network Time Protocol (NTP). However, increasingly computer networks are synchronised using NTP servers that receive the time from GPS signals (Global Positioning System). These are generated by atomic clocks on board the satellites and are available as a source of atomic time anywhere on the globe.