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Proper time
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Time measured by a clock moving with the object.
The time measured by a clock along its own worldline, dτ = dt/γ. All observers agree on it and it is the 'wristwatch time'.
Astronaut's own clock.
Maximised along the straight (inertial) path.
In more detail
Proper time is the time measured by a clock moving with an object. It is the invariant time interval and is always the shortest between two events in spacetime.
Real-world uses
- Proper time is used in calculating the ages of traveller clocks.
- It defines the time experienced by moving particles.
- Engineers compute how much time passes on a fast-moving spacecraft using the proper time along its path.
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Frequently asked questions
How does proper time differ from coordinate time?
Proper time is measured by the moving clock, while coordinate time is measured by a stationary observer.
Why is it shortest?
Because moving clocks run slower, the path with the least proper time is the straight one in spacetime.
What is proper time?
The time measured by a clock that travels along with the object, so it is the time experienced locally.
Related topics in Relativity
Spacetime diagrams · Spacetime interval · Light cones and causality · Relativistic momentum · Relativistic energy · Rest energy