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Happy Birthday, Louis Essen 04.09.15


This Sunday, 6th September, Louis Essen OBE FRS would have been 107. The physicist, who died in 1997 at the age of 88 found fame for building the world’s first working atomic clock and helping to introduce the atomic timescale.

This year remembering Essen’s birthday is even more poignant, as it coincides with the 60th anniversary of the construction of the aforementioned first ever working atomic clock at the National Physical Laboratory (NPL) in Teddington.

Essen was invited to join NPL after completing his physics degree at Nottingham University in 1928. Initially he worked on the development of quartz crystal oscillators, which could measure time as accurately as the best pendulum clocks. Then during the Second World War, his work on high-frequency radar led him to develop the cavity resonance wavemeter, which he used from 1946 with Albert Gordon-Smith to measure the speed of light more accurately than any previous measurement.

In the postwar years, Essen became interested in research in the US about the possibility of producing a highly accurate clock based on atoms. This led, in 1955, to Essen and Jack Parry designing and building the world’s first working caesium atomic clock at NPL, transforming the way we measure and use time. This was the first clock to keep time more accurately than the rotation of the Earth.

To celebrate the 60th anniversary of the first atomic clock a new book has been published containing the memoirs of Louis Essen. The book includes a chapter written by NPL Fellow Patrick Gill on the future of atomic timekeeping and is published by Ray Essen, Louis’ son-in-law. Louis Essen retired in 1972, having spent his entire working life at NPL. He wrote his memoirs in 1996 and they provide an accessible and non-technical record of his work, together with a few personal details. Louis’ legacy at NPL remains strong, and will do for some time.

The caesium fountain atomic clock used at NPL today can measure time to an accuracy of one second in 158 million years. The next generation of atomic clocks at NPL, using laser-cooled trapped ions or atoms, should achieve accuracies around 100 times better than the current best atomic clocks – equivalent to gaining or losing no more than one second in the lifetime of the universe.The current atomic clock system at NPL is the basis of UK time and contributes to the international time scale, Coordinated Universal Time (UTC). People may ask why we need such accuracy in our time scale. The answer is that critical elements of the UK’s infrastructure, from global communications to satellite navigation, are underpinned by the stability and accuracy provided by atomic clocks. So we still benefit from the work Louis Essen did throughout his long career at NPL, so spare a thought and find the time to wish him a happy birthday this Sunday.

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