Is anything even real? What does it mean to ask if something is real or not? Is it real like a rock is real? Is it real like love is real? Is it like a hallucination is real for the person having it? Is it real like the idea of a unicorn or a dragon is real? Is gravity real? Is the gravitational theory real? Am I real?

Regarding the concept of time, I believe Aristotle pretty much nailed in its essence: time a parameter to measure evolution or change. What Aristotle couldn't be expected to understand is time's intricate relationship with space, i.e., the space-time geometry that is proposed in special and general relativity and which constitutes our most successful model of space and time so far.

Is there more to the nature and physics of time than what we've already uncovered? It is very likely so, and I'd bet that we will eventually understand it better. Maybe we must integrate aspects of time perception and consciousness into the picture. Maybe the proposed space-time geometry is just a simple version of some more general and insightful geometrical structure. Whatever the case, the simple truth that Aristotle stated remains as the very basic nature of time.