You likely interact with atomic clocks every day without realizing it:
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:
Since 1967, the International System of Units (SI) has defined one second as exactly 9,192,631,770 oscillations of the radiation produced by this transition in a cesium-133 atom. Why It Matters Atomic Clock
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.
High-speed data transfers and cellular networks require perfectly synchronized "stamps" to ensure packets of data arrive in the correct order. You likely interact with atomic clocks every day
Stock exchanges use atomic time to log trades down to the microsecond, preventing fraud and ensuring a fair "first-come, first-served" system.
If the microwave frequency is exactly right, the atoms change states. Why It Matters The best modern atomic clocks
Scientists use these clocks to detect tiny changes in gravity (General Relativity) and to search for dark matter. Precision Limits