What is time?
Time is a variable, It comes into existence when space if formed It is considered to be the fourth dimension of the universe.
In this equation Distance, and Time both are variable that can change. Time changes with the velocity. The faster something travels the slower time changes. At the speed of light time stops and no longer exists. For light or anything without mass that achieves the speed of light time does not exist.
Even electrons that have a small amount of mass time and distance does not seem to matter. An single electron with a choice of two slits will travel through both of the slits at the same time. These apparently contradictory observations lead to the ideas of quantum mechanics and further quantum field theory. The electron is able to go through both slits because it is a wave. More precisely, the electron time evolution satisfies a complex wave equation.
Time also changes with mass. The greater the gravitational field the slower time changes. At a singularity boundary of an infinite mass thought to exist at black hole time stops. It could be said that time is both infinite and non existent at a singularity.
Without space it is difficult to imagine how time could exist. The fourth dimension is part of the the other three dimensions. Before the beginning of the present universe ( The Big Bang?) neither time nor space existed.
Time is a variable it can change with both mass and velocity. Time is a part of space and is considered to be the fourth dimension of the universe.
Time is the fourth dimension of four dimensional spacetime.
In the 17th century, time was thought to flow continuously from past to future. Everyone's clock ran at the same rate. Newton's laws of motion are based on this assumption of absolute time. It was also thought that space was absolute. Every position could be
measured with respect to a fixed frame of reference.
Developments in the late 19th century showed that neither space nor time are absolute. This led to the theories of relativity. We now know that the universe is a four dimensional spacetime. There are three spatial dimensions and time is the fourth dimension.
If spacetime is completely flat then time passes at the same rate for everyone. In fact spacetime is curved. The very presence of mass, energy and momentum causes spacetime to curve. For most observers, the region of spacetime they are in is flat. That means that every observer sees their clock ticking at the same rate.
Consider two observers each in their own spaceship travelling apart at a fixed velocity. Neither observer can tell if they are travelling faster or slower than the other unless they have a reference point such as a star. Each observer sees their clock ticking at the same rate. Each observer also sees the other observer's clock ticking slower.
So, what is happening? Well, everything is travelling at the speed of light. Each observer is travelling at the speed of light in the time dimension of their local spacetime. When you observe the clock of another observer who is travelling at speed or in a gravitational
field, their time dimension is curved away from yours.
Think of being on the top of a mountain watching a skier descend the step slope of the mountain. The skier is travelling fast but the horizontal velocity from you is relatively slow because the biggest component of the skier's velocity is vertically down. Now imaging that the horizontal direction is time and the vertical direction is space. The fact that the an observer is travelling at speed in space relative to you means that the observer is travelling
slower in time relative to you. The combined speed in both space and time is the speed of light.
Time is how fast you are travelling in the time dimension of spacetime.