Interesting how many comments there are on this topic!
I will reiterate and try to simplify other posts;
Like distance-measuring tools which use standardized lengths to describe distance, time is standardized motion (Falling grains of sand, number of blinks, atomic oscillations, planetary rotations, etc.) that is used to describe motion.
All the elements of "spacetime" are required to describe motion; x,y,z,and t, which leads me to believe that motion is the basic nature of the uni(?)verse.
I believe Einstein was simply showing that time could not be used as a constant due to differing perceptions of time based on the relative orientation of observers. He suggested the speed of light as a constant and things got screwy when it was found that gravity deflects photons... Hard to find a good vantage point to observe from when your planet is spinning while orbiting a star that is orbiting a black hole that is streaking through the universe...
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