tidsskalaer

Tidsskalaer, or time scales, are systems for measuring and coordinating time across different contexts and orders of magnitude. They range from sub-second intervals used in physics experiments to the vast durations of geological and cosmic history. Time scales are defined by units, standards, and reference frames, and they must account for both the regularities of clocks and the effects of relativity and Earth’s rotation.

Key time standards and units include the SI second, defined by the cesium-133 atom. Practical scales built on that unit include International Atomic Time (TAI) and Coordinated Universal Time (UTC). UTC inserts leap seconds to stay close to mean solar time, while UT1 reflects the actual rotation of the Earth. In relativistic astronomy, higher-level coordinate time scales such as Terrestrial Time (TT), Barycentric Dynamical Time (TDB), Geocentric Coordinate Time (TCG), and Barycentric Coordinate Time (TCB) are used to describe time in specific reference frames and for precise ephemerides. Proper time is the time measured by a clock along its worldline, distinct from these coordinate scales.

Geologic and cosmic time scales describe much longer histories. Geologic time divides Earth’s history into eons, eras, periods, and epochs, spanning hundreds of millions to billions of years. Cosmic time includes the age of the universe (about 13.8 billion years) and fundamental short-time concepts such as Planck time (~5.4 × 10^-44 seconds), the earliest meaningful interval in physics.

Applications of tidsskalaer include navigation, astronomy, climate science, and geology. Differences among scales arise from clock behavior, Earth’s rotation, and relativistic effects, making clear definitions and appropriate references essential for accurate measurements and communication.