How do you define Time?

we can define time ??? '' INTERVAL BETWEEN TWO HAPPENINGS IS TIME''

wow man if time dznt exist than tell me whats ur age? whats the age of our planet? and whats the age of our universe????

E = mc2

There are the conventional "objective metrics" of clock and calendar times and the subjective sense of duration which sometimes goes fast (when I'm having fun) and sometimes slowly (when I'm impatient or bored). Then there's the physicist's notion of time (T), which I suspect in my ignorance is something different.

Amirwaraich, is "time" that which you are saving by writing "ur" instead of "your"?

Amirwaraich, is "time" that which you are saving by writing "ur" instead of "your"?

time is a spontaneous change.

I define time as a value given meaning by measurement.
Similar values are length, width, depth etc.

Within a three dimensional space, an object can move on all three spatial axis, or on just one of them.
Regardless, it moves along a fourth axis. We do not perceive this movement, because everything we perceive moves in tandem with us. Similarly, if you are floating down a stream, a piece of wood that floats next to you will appear to be standing still relative to you.
Time is this stream, and we don't perceive it directly because we are caught in it's flow. Instead we see things changing, and thus, as a result of having memory and the ability to anticipate what will happen, time is perceived almost as an entity.

But it is really just duration, another form of movement, along another axis that we can't directly perceive.

Lets put it like this. If you had 2 dimensional perception, you would not be able to see things that move along the third dimension. All you would see of them would be an infinitely thin cross-section of it as it passed through the dimensions you could see.

Us having a three dimensional perception, we cannot pereive things that move in the fourth. All we can see is an infinitely thin cross-section of it, and we name that cross-section "the present".

From that we deduce "the past" and "the future" and assume that time is linear, which only makes sense when we compare it to other kinds of linear movement such as moving up and down or left and right in a three dimensional space.

So if nothing happened, time would not stop. Same as if you don't move anywhere, distance doesn't disappear. But neither would have much meaning or functionality to us.

Everything ages even if we don't "see it."

But what if we had no memory? What if we had no way to remember how something used to be before it changed? Would we be able to perceive aging? Would we be able to know that it happens?
And if we could not know it, would it be true?

Time happens regardless of human existence. The real question is whether other life forms and everything in space reacts to time.

Does the sun have a life span?

That's just it. Change happens regardless of humans. Time is the axis we have drawn to measure it, just as we have three spatial axis to measure spatial movement.

And, of course, time is related to space: the longer it takes to get from one place to another at a given speed the greater the space between them (and the greater the space between them the greater the time needed to go from one to the other)....
And I've heard that time is the way we avoid everything happening at once...

It makes more sense to me to think that everything does indeed happen at once.
There is only one infinitely small moment in which things change. Fortunately, this moment seems to never pass.

Cryacuz, two interesting notions, viz., everything occuring in a kind of impossible-to-understand ETERNAL or TIMELESS PRESENT and everything happening at once. I can't grasp them cognitively (maybe a theoretical mathematician can), but I do have the sense that as soon as I am dead I will have lived forever--my subjective forever--that is to say for "me" nothing existed before I was born and nothing will exist after I'm dead.
Also interesting that you separate time and change: you said that "There is only one infintely small moment in which things change. Fortunately [you add], this moment seems to never pass."
I said long ago in a thread on time that I prefer a lake to a river metaphor when discussing time. The river image suggests a downstream-as-the past, an upstream as a future (and they exist simultaneously) and the present which is like a boat in which we are floating. Because up and down streams exist at the same time this metaphor supports a fantastical notion of time-travel, leaving the boat and going either into the future (upstream) or the past (downstream).
A lake metaphor has only a present in which everything (the water's surface) is continuously changing. No time travel, only an eternal present containing change.

I agree that a lake, or an entire circular system of water, from cloud to ocean tide, is a better metaphor.

But to my thinking, there is no fundamental force behind the three axis of spatial movement. Our three dimensional model is a psychological construct that allows us to precisely measure and predict movement.

Similarly, there is no fundamental force called time. It is a psychological construct that allows us to make sense of things. We have identified a progression of processes that we use to quantify change relative to other change, and the movement through these intervals is what we call time.

Imagine if we were running one hundred meters, and referred to our movement past each yardstick as 'space'. It would be kind of misleading. It would suggest that space is not the emptiness between objects, but the behavior of objects themselves.
Similarly, time could be thought of as the emptiness between events, while a traditional idea of time, or perhaps language itself, leads us into thinking of this emptiness as an actual thing or force driving things to change.

How humans measure time is simply based on our cycle of night and day. That's a measurement only humans understand and relate to, although nature has a way of adhering to this cycle - even in terms of our seasons.

That statement is a bit misleading in my opinion. Everything that undergoes change does so according to the rules and restritions of the processes that are taking place. This gives meaning to the concept of time when we compare one changing event to another.

That is all time does for us. It puts things in relation. It takes 365 laps around the sun for a full year. One hour is sixty minutes, which is approximately 1/24 of the time it takes for the earth to rotate once. It is a system of relativity, and without the ability to perceive connections between different events, the concept is meaningless.

It's seems to me we are more in agreement than you think.

The measurements you describe are what humans use as time in our universe. We rely on our sun to determine 'our' time.

I'm not sure how anything outside of our universe in measured.