Question

What is the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133atom?

Answer 1

The duration is one second
This is the standard measurement of a second
When the cesium second was defined in 1967, it was based on a measurement of the number of cycles of the radiation from a particular cesium-133 transition with reference to the second commonly used in civilian timekeeping, which at that time was based on astronomical observations. The objective was to improve the stability of timekeeping in a manner that would be invisible to the general population. The decision to redefine the second was ultimately that of the International Committee of Weights and Measures, an organization that works to standardize and coordinate measurements. At its 13th official meeting in 1967, the committee adopted the following definition: "The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."
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