The unit of time is defined more accurately by an atomic clock because it relies on the natural and constant vibrations of atoms. Atomic clocks use the oscillations of atoms as a reference to measure time with extreme precision.
Traditionally, time was measured using astronomical phenomena like the rotation of the Earth or the motion of celestial bodies. However, these methods have limitations and can be influenced by various factors, such as gravitational effects, irregularities in the Earth's rotation, and other external forces.
In contrast, atomic clocks are based on the behavior of atoms, particularly the oscillations of electrons or the vibrations of atoms themselves. The most commonly used type of atomic clock is the cesium atomic clock, which measures the frequency of microwave radiation emitted by cesium atoms as they transition between energy levels. This frequency is extremely stable and reproducible, making it an excellent reference for defining the unit of time.
Atomic clocks offer several advantages:
Accuracy: Atomic clocks are incredibly precise and can measure time intervals with accuracies of a few billionths of a second. They are not subject to the fluctuations and irregularities associated with natural phenomena.
Stability: The vibrations of atoms used in atomic clocks are highly stable over time, allowing for long-term accuracy and consistency in timekeeping.
Universality: Atomic clocks provide a standard reference for time that is consistent across the globe. This enables synchronization of timekeeping systems worldwide and facilitates precise scientific measurements and technologies such as GPS.
Definition of the second: The International System of Units (SI) defines the second as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two energy levels of the cesium atom. This definition, based on atomic clocks, provides a fundamental and universal reference for the unit of time.
Due to their extraordinary accuracy and stability, atomic clocks have become the cornerstone of modern timekeeping and are used in various scientific, technological, and everyday applications.