The National Physical Laboratory (NPL) has been recognised as the birthplace of modern timekeeping.
The European Physical Society is to award the National Physical Laboratory ‘Historic Site’ status as the birthplace of atomic timekeeping.
In 1955, whilst working at NPL, Louis Essen designed and built the world’s first successful atomic clock. Based on the frequency of a transition in caesium atoms, it was able to keep time more accurately than the best pendulum or quartz clocks available, and was less variable than the Earth’s rotation.
In the years that followed, Essen used the NPL caesium clock to measure the relationship between the chosen caesium frequency and the astronomical second - leading directly to the redefinition of the Système Internationale d’Unités (SI) second in 1967 in terms of the caesium frequency.
And these clocks have steadily been improved over the past 50-plus years. Today, the best caesium clocks - known as 'caesium fountains' - are accurate to 20 picoseconds (20 trillionths of a second) per day. UK’s national time scale, for which NPL has had sole responsibility since 1985, is based on its own caesium fountain, known as NPL-CsF2.
NPL is also playing a leading part in the development of a new generation of atomic clocks; these employ optical frequencies, which promise a further substantial improvement in accuracy.
We congratulate NPL on its recognition as the birthplace of modern timekeeping.
- 20 December 2013