Atomic fountain clocks are becoming still more stable
Caesium fountains are more accurate than 'normal' atomic caesium clocks, because in fountains the caesium atoms are cooled down with the aid of laser beams and come ever slower - from a rapid velocity at room temperature to a slow 'creep pace' of a few centimetres per second at a temperature close to the absolute zero point. Thus, the atoms remain together for a longer time so that the physicists have considerably more time to measure the decisive property of the caesium atoms which is required for the 'generation of time': their resonance frequency. When a maximum of atoms has changed into an excited state, the frequency of the exciting signal is measured - those approximately nine billions of microwave oscillations which must elapse until exactly one second has past...