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### Time dilation

**Time dilation** is the phenomenon that, according to an observer, the time of another observer is slower.

##### Explanation

Time is not a constant factor. You can calculate this with the special theory of relativity. When the speed increases, the time goes slower. The maximum speed is the speed of light, which you cannot reach, because then time would no longer run.

##### Calculation

The lorentz transformation for the time is

In this transformation *t'* is, according the observer, the time perceived by the moving object and *t* is the time experienced by the observer. From this we deduce the time dilation as

Because 0 < *v*^{2} < *c*^{2} the lorentz factor is greater than 1, so

##### Conclusion

In a moving object, time really slows down. This is **astonishing**.

## HistoryThe German physicist Albert Einstein showed in 1915 that this effect concerns the nature of time itself. |