Ok, this one will be challenging…
Time is a linear, irreversible and sequential measuring of the duration of events and the intervals between them. Time is the forward progression exerted upon all matter and categorized by three states: The past (what it was), the present (what it is), and the future (what it will be). It, like most things in the universe, are relative to the observer. For example, if a tree had sentience it would perceive time differently than a human. Our observations of time are limited by a few factors; the relative speed with which we move through our universe, and how long our expected continuum of life is (life expectancy). If we lived for thousands of years, a minute to us may feel more like a second now.
In the simplest of terms, “the rate at which time passes depends on an object’s velocity relative to the speed of light and also on the strength of intense gravitational fields.” Time is often described as the fourth dimension. For example, in three dimensional mathematics, you need three coordinates to pinpoint a location. By adding a fourth dimension (time) you can locate events. This conception makes it (slightly) easier to understand the notion of spacetime. Physicists used to think that space and time were two separate things, but Einstein theorized that they were connected (although he wasn’t the first).
Spacetime is independent of any observer, yet time as experienced is relative to an observer. This is the one of the consequences of Einstein’s theory of special relativity. Simply put: The closer an object approaches to the speed of light, the slower time goes (for the object). This has been proven many times since Einstein first theorized it. In one experiment, atomic clocks were created (I’m not sure of their margin of error, but it’s something ridiculous like it’s accurate to .0000000000000000001 seconds). One was left on the ground, and the others were flown eastward and westward, respectively. “Relative to the atomic time scale of the U.S. Naval Observatory, the
flying clocks lost 59+/-10 nanoseconds during the eastward trip and
gained 273+/-7 nanosecond during the westward trip…” The jets had effectively traveled through time (as we see it). So, with Einstein’s model, a person can travel forward in time simply by taking a spacecraft that flies at (near) the speed of light and making a round trip to and back to Earth. They will have aged little, but hundreds of years will have gone by on Earth. One other thing can affect the “speed” of time too: gravity. According to Einstein’s (what a guy) theory of general relativity, the more mass an object has (and therefore more gravity), the more effect it has on time. If you had two synchronized clocks, and put one on a planet with low gravity, and one on a planet with high gravity, the clock on the low-gravity planet would appear to run slower.
Time is such a hard thing to define, since you have to talk about the intrinsic (first paragraph), the scientific (second and third) and the quantifiable aspects. Not just “what time is” but also how we perceive and measure it. We owe our perception of time to that beautiful ball of burning gas hanging in the sky. Even though, with the invention of electricity, day and night no longer have as deep a significance (night jobs and such), our entire way of life has been built upon the cycles of the Sun, and axial orbit, and our orbit around the Sun. This is how we define time, or at least duration of time. If we lived on Mars, a year would last almost twice as long.
I sure hope this was helpful, and coherent enough. I love questions like this, they really get me thinking, and I learn a lot in the process of research. Thanks!