The best modern atomic clocks are so stable that they wouldn't lose or gain a single second in —a span of time longer than the age of the universe.
At the heart of the clock is a physical constant: the "resonant frequency" of an atom. When atoms are exposed to specific frequencies of microwave or light energy, their electrons jump between energy levels. In a standard cesium atomic clock: Atomic Clock
Scientists use these clocks to detect tiny changes in gravity (General Relativity) and to search for dark matter. Precision Limits The best modern atomic clocks are so stable
GPS satellites carry atomic clocks. Because radio signals travel at the speed of light, even a billionth of a second of error could result in your GPS being off by several miles. In a standard cesium atomic clock: Scientists use