Louis EssenBorn 6 Sep 1908; died 24 Aug 1997 at age 88.English physicist who invented the quartz crystal ring clock and the first practical atomic clock. These devices were capable of measuring time more accurately than any previous clocks. He built a cesium-beam atomic clock, a device that ultimately changed the way time is measured. Each chemical element and compound absorbs and emits electromagnetic radiation at its own characteristic frequencies. These resonances are inherently stable over time and space. The cesium atom's natural frequency was formally recognized as the new international unit of time in 1967: the second was defined as exactly 9,192,631,770 oscillations or cycles of the cesium atom's resonant frequency, replacing the old second defined in terms of the Earth's motion. |
