Time is an independent time dimension in four-dimensional space, which is produced by the movement of three-dimensional space. Length, width and height are three-dimensional, and internal and external movements produce four dimensions. Just like watching a movie with a progress bar, the time depends on the specific people and animals. There is no time to exist alone. For example, there is no time in a vacuum, time is made of stones, and the countdown to life and death.
The theory of time in relativity shows that time is elastic, not constant, and depends on the motion state of two reference objects.