Many people say time is an illusion. Maybe, maybe not. But if it is an illusion, it is a real illusion: the illusion really exists!
Maybe it's "observer-driven", subjectively, so that the "speed" of time is faster or slower according to the observer, and for an observer on a galactic scale, time passes more rapidly than at a planetary scale, and that for an observer as large as the whole of reality, the speed of time is infinite, and in effect there is no time.
For an observer on the scale of the whole of reality, every particle and part may be quantum-entangled, so that interaction is faster than the speed of light. So much faster that "speed" becomes meaningless, and the interaction is in fact instantaneous, ie without any time at all.
Or maybe time is just another way we humans measure space, along with "length", "breadth" and others. Some of those we deem "spatial" and some we deem "temporal", as if there are two categories that are qualitatively different. But maybe they're not qualitatively different. Maybe that's just our own hangup/perspective. Maybe "time" is just another humdrum sub-dimension along with "breadth" and "length". Or even "gravity", for that matter!
As for the purpose of time, in a trivial sense, it's to help us make and keep appointments. To plan for the "future" from a perspective in the "present", each instance being an example that "the three times are one" (past, present, future).
Noting that some futures are quicker than others, or is it that some presents are quicker than others? Not that they arrive quicker, but rather are fundamentally "coarser-grained". Whatever the case, in all cases, it would be observer-driven and subjective.
So maybe both nature and purpose of time are observer-driven and subjective, ie relative, with one exception, and both terms only have currency within a certain context, ie human, and do not have universal application, necessarily.
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