The best long-term accuracy in the ticking of time can be found in an atomic clock – called CsF2 – at the UK’s National Physical Laboratory (NPL) new studies claim would lose or gain less than a second in some 138 million years.
The NPL’s clock is a "caesium fountain" atomic clock, in which the "ticking" is provided by the measurement of the energy required to change a property of caesium atoms known as "spin". According to international standards, one second of time is equal to 9,192,631,770 peaks and troughs of the electromagnetic waves required to accomplish this "spin flip".
The NPL-CsF2 clock provides an "atomic pendulum" against which the UK’s and the world’s clocks can be compared, ensuring they are all ticking at the same time.
There are six high-precision atomic pendulums in the world: apart from the CsF2 in the UK, there are two in France, and one each in the US, Germany and Japan. For them, absolute accuracy is a tireless pursuit. The International Bureau of Weights and Measures (BIPM) in the outskirts of Paris is responsible for checking and correcting their accuracy. At the last count in 2010, the UK’s atomic clock was on a par with the best of them in terms of