t0

t0 is a symbolic label used in many disciplines to denote an origin or reference time. It typically represents the starting point of an interval, process, or observation, from which elapsed time is measured as t − t0.

In physics and cosmology, t0 often marks the origin of a model's time axis. It may denote the initial condition of a dynamical system, the start time of an experiment, or, in cosmology, the present cosmic time chosen as a normalization point (for example, the scale factor a(t) is frequently defined so that a(t0) = 1).

In signal processing and control theory, t0 is used to align or shift signals in time. A time-shifted signal is represented as x(t − t0), where t0 is the shift amount. In scheduling or event logging, t0 can serve as the time origin for a sequence of events or tasks.

In statistics and data analysis, t0 may designate a baseline or null value for a parameter in a time-dependent model or hypothesis testing, depending on context. The precise interpretation of t0 is defined by the model or experiment being described.