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### Proper time

The proper time τ is the time that passes on a certain world line.

##### Explanation

In relativistic theory, proper time of a particle is the time measured in the area of this particle, that is in the area where it is immobile.

##### Example 1

The Lorentz factor can be written as

where

tTime τProper time

##### Additional information

The German mathematician Hermann Minkowski introduced the notion of proper time in 1908.