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A Greek tau, the time a clock actually reads.
Also known as: Proper time, Worldline time, Tau in relativity
Proper time is what a clock travelling with an object measures, and unlike coordinate time it is the same for every observer. That invariance is why the twin paradox has an answer: the twins' proper times genuinely differ, and everyone agrees about which is smaller.
Denotes proper time: the time elapsed along an object's own worldline, as measured by a clock carried with it.
Contexts: Laboratory
Is invariant across reference frames, unlike coordinate time, which is what makes it the physically meaningful quantity.
Contexts: Laboratory
Collides with torque, the time constant and the tau lepton, all written tau.
Contexts: Laboratory
A Greek lowercase tau, a horizontal stroke with a curved descending stroke from its centre.