During the last 50 years the revolution from cuckoo clocks to caesium clocks has gone largely unnoticed yet many inventions  from satellite navigation (GPS) to the Internet itself rely on clocks that measure time to an 
accuracy unheard of only a few decades ago.

At the centre of much of this change has been the work of a controversial British physicist, Louis Essen. Known as "Old Father Time", Essen built the first atomic clock, accurate to one second in 300 years - sufficient to detect minute irregularities in the spin of the Earth itself.

Essen soon realised that the definition of the second of time had now become a major block to realising the potential of his new clock. 

It took a further 12 years before astronomical time ceased to exist. Essen fought to change the way the second is defined. Finally, in 1967 it was agreed internationally that the second should not be linked to the duration of the day or year (both of which vary) but to the natural periodicity of an atom of caesium.

Essen worked for 44 years as a civil servant at the National Physical Laboratory (NPL), Teddington; retiring in 1972.

He angered the Royal Society and the British government in the early 70’s when he published criticisms of Einstein’s special theory of relativity.

Two of the basic measurements in physics, time and length, have both been transformed due to Essen’s work. The basis of time measurement has switched from astronomy and the solar system to physics and the properties of the atom. His revised value for the velocity of light led to a further change in which length is now defined, not in terms of a metal bar, but the velocity of light multiplied by time. Essen is the only British physicist ever to have been honoured for his contribution to science by both the USA and USSR during the Cold War.

He received the Rabi Award from America and the Popov Medal from the former Soviet Union. 

“John Harrison (who solved the Longitude problem) benefited sailors all over the world and Louis Essen has done something similar for the space voyagers of the future”.

Time for Reflection

Time for Reflection is a short autobiographical account of Essen’s work on Time Measurement and his 
controversial doubts about Einstein’s special theory.

It was written in 1996, the year before his death, and is reproduced here un-edited.

Famous for a Second

Famous for a Second is the title of a forthcoming book about Essen’s work and how it led him into a number of protracted struggles with the scientific establishment, resulting in the suppression of some of his work.

This book will describe how international scientific discoveries are made – and what can go wrong along the way. The story shifts between Britain, America and Russia as world-class laboratories competed not just for research funding but for status and the commercial jewels that can follow.

Famous for a Second is not only a book about a key discovery in the history of science, it is also a social documentary about a body of scientists and how the results of their research have changed the world in which we live.

Essen’s controversial views have caused him to be labelled a trouble-maker and dissident by some.The physicist who built the first atomic clock was finally stopped from writing about time in the mainstream scientific press!

The story begins with the development of radar during the War and how military secrets passed to America. Later, some of the same scientists tried to make an atomic clock in America.  Although beaten by Essen and his team, they went on to build commercial models that led to a proliferation of new uses for atomic time. 

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Related Pages

• A List of Essen’s published papers
• The Early Years
• Quartz Rings
• The War Years
• Velocity of Light
• The Atomic Clock
• Relativity
• Time Signals
• Afterthoughts