absolutetime

Absolute time is a concept in philosophy and physics describing time as a single, universal, objective parameter that flows uniformly, independent of any observer or events.

Historically, in Newtonian mechanics, time is absolute: a true clock that ticks the same for all observers. This contrasted with relational theories of time, notably proposed by Leibniz, which held that time derives from the relations among events rather than existing independently.

With Einstein's theories, the notion of universal absolute time was superseded. Special relativity posits that simultaneity and elapsed time depend on the observer's frame of reference; time is part of spacetime and measured by proper time along worldlines. General relativity further shows that gravity affects time, so there is no single universal time across the cosmos. In cosmology, a commonly used coordinate time—cosmic time—offers a convenient slicing in expanding universes, but it remains a coordinate, not a universal physical time.

In modern practice, the term "absolute time" is rarely used in physics; instead time scales such as International Atomic Time (TAI), Universal Time ( UT1, UTC), and cosmological coordinate times are used as standards for measurements. In computing, "absolute time" can refer to timestamps anchored to a fixed epoch (for example, Unix time since 1970-01-01), used to order events and compute durations, in contrast to relative time intervals.