We all know what time is — we experience it every moment of our conscious lives. If there is one thing that we all have in common, it may just be the passage of time as we get older.
But once you actually start trying to provide a definition of time, it eludes our grasp as if it was so much mist. Trying to come up with an explanation without using self-referential terms seems really difficult.
Maybe someone else will have better luck than me: What is time?
Related questions: What does “now” mean? Is free will important? What do we have in common?
Perhaps time could be described as “the linear interaction of forces and physical objects.” The same object, the moon, for example, exists and has existed at a myriad of points along a continuum of time (one that is basically unfathomable to human minds). But the moon has not been identical from one point on that continuum to the next. It has been subjected to a flow of physical change which resulted from its interaction with other objects — the earth, meteors, humans in little space suits — and the forces that govern their interactions. The interactions flow only in one direction (as far as we can tell from our limited perspective, anyway), and their effects are cumulative.
On the other hand, I have been using a personal “working definition” of time for several years, one that is unabashedly self-referential. I’ve pictured time, in the human mind, as a dynamic hourglass, with all possible objects and interactions being funnelled into a smaller and smaller set of possibilities leading up to the present moment. As circumstances shift, and there are fewer possible outcomes, the hourglass narrows.
For example, let’s set the “waist” of the hourglass, which represents the present moment of my life, at 11:00:00 am next Saturday. At that point I might be at home doing laundry, or meeting friends at a museum, or visiting family up North. If I’m up North, I might be out running, or having brunch, or sitting on the dock reading a book, or talking with my mother. What actually happens depends in part on who is there, and what the weather is, and if anyone thought to bring eggs and bacon. By the time that moment has nearly arrived, the wider set of possibilities will have been winnowed down to just a few. The waist of the hourglass ultimately represents What Actually Happens.
What’s interesting is what happens to time after The Moment passes. I myself can only exist in the crucible of The Moment, the bright ring that moves one direction only, even though I can cast myself virtually forward and back via my own mind. But what happens to 11 am Saturday after it has passed, and I have moved on to 11:01? Its existence in physical objects is gradually erased like wave after wave on a sandy beach. The eggs are digested, the shells thrown out, the frying pan scrubbed. The memories of those who were there for that moment, already limited by their perspective, begin to fray out, some slowly, some rapidly. The Moment did exist – after all, only a certain set of things happened during that second. But once it passes from possibility to reality and is “frozen” in that state, the hourglass widens again, as the records and recollections of that moment dissolve. Five hundred years in the future, determining what happened at that time and in that place could be almost as difficult as predicting it five hundred years before it happened.
This thing all things devours:
Birds, beasts, trees, flowers;
Gnaws iron, bites steel;
Grinds hard stones to meal;
Slays king, ruins town,
And beats high mountain down.
Thank you for answering in the form of a question. 😉