SI second

The SI second is the standard unit of time used worldwide, defined by a precise scientific measurement rather than a physical object. It is based on the vibrations of cesium atoms: one second is the duration it takes for exactly 9,192,631,770 cycles of the microwave radiation emitted when a cesium-133 atom changes energy states. This atomic definition allows for extremely accurate and consistent measurement of time, which underpins everything from global positioning systems to scientific experiments, ensuring a common, precise understanding of one second across various disciplines and technologies.