Timekeeping with caesium on the BBC
An episode of the BBC World Service's Elemental Economics series, focusing on the element caesium, featured scientists at the National Physical Laboratory (NPL) speaking about the caesium fountain atomic clock and NPLTime®.
NPL's Leon Lobo and Krzysztof Szymaniec explain some of the science behind the caesium fountain and why there is a need for such accurate timekeeping. The show was presented by the BBC's Justin Rowlatt and also featured scientists from the International Bureau of Weights and Measures (BIPM) and UCL.
Ever more accurate timekeeping devices have always been at the forefront of new technologies and, as technology progresses, the accuracy required increases. The introduction of national railways in the 19th century meant that clocks in Manchester and Bristol had to be synced with London to an accuracy of under a minute. Nowadays, with the development of GPS technologies, telecommunications and algorithmically-controlled stock market exchanges, globally-synchronised clocks need to operate with microsecond or even nanosecond accuracy.
NPLTime® is a precise time signal which is directly traceable to Coordinated Universal Time (UTC) and independent of GPS. The BBC programme explains how NPL's commercial timekeeping services can benefit the financial sector, telecommunication services and the national electrical grid for network synchronisations.
NPL is home to the caesium fountain atomic clock (NPL-CsF2), which is accurate to one second in over 150 million years and contributes to the international timescale UTC, as the UK's primary frequency standard. In the 1950s it was discovered that atomic clocks are in fact more regular than the spinning of the Earth, so the old definition of a second - as a fraction of the time it takes the earth to rotate on its axis - was abandoned in favour of the new, more precise definition in terms of a microwave transition in caesium.
This current definition may itself be replaced in years to come, as the next generation of optical atomic clocks, which use elements such as strontium or ytterbium, have potential accuracies of one second in 14 billion years. That means they would only lose one second in time since the Big Bang.
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