General relativity has changed our understanding of space and time. ...The spacetime of general relativity ...is likely to be just a classical approx… - Carlo Rovelli

[I]n pre-relativistic mechanics, time is a special physical quantity, whose value is measured by physical clocks, that plays the role of the independent variable of physical evolution.

A handful of types of elementary particles, which vibrate and fluctuate constantly between existence and non-existence and swarm in space even when it seems that there is nothing there, combine together to infinity like the letters of a cosmic alphabet to tell the immense history of galaxies, of the innumerable stars, of sunlight, of mountains, woods and fields of grain, of the smiling faces of the young at parties, and of the night sky studded with stars.

When two friends meet... after one has lived in the mountains and the other at sea level, the watches... will show different times. ...Neither is truer than the other. ...Times are legion: a different one for every point in space. ...there is a vast multitude of them. ...Every clock has its proper time. ...Einstein has shown how to calculate the difference... The world is not like a platoon advancing at the pace of a single commander. It is a network of events affecting each other. ...Physics does not describe how things evolve "in time" but how things evolve in their own times, and how "times" evolve relative to each other.
Time has lost... its unity.