Time is a real phenomenon a continuous change through which we live. Time becomes evident through motion. Sunrise and sunsets, night and day, the changing seasons and everything else is indicative of continuous change.Time is a measure in which events can be ordered from the past through the present into the future, and also the measure of durations of events and the intervals between them. Time is intangible. It can only be experienced. And thus, we experience every moment of every day.
But the question here is ‘Is it same for everyone?’ The answer would have been ‘Yes’ if it wasn’t for Albert Einstein to find out otherwise. Einstein formulated the theory of relativity which quotes :
All motion must be defined relative to a frame of reference and that space and time are relative, rather than absolute concepts: it consists of two principal parts. The theory dealing with uniform motion is called special relativity and the theory dealing with gravity is called general relativity.
According to this theory, there exists no such thing as absolute motion or absolute rest. He explains that all objects move relative to each other. Thus, when we say that an object moves faster, we say that in accordance to another object that moves slower, even though it may appear stationary to us. To explain it better, we can take the example of two people travelling in a train at a uniform speed. Despite of the train being in motion, the two people in it observe each other as stationary objects as the train and those two are moving at the same speed. Thus, all the law of physics stand same as when you are standing on the ground. Now, for a third person standing on the ground, he is stationary and the other two people are moving at the same speed of the train. But, is the third person standing comely still? No.
The earth is continuously in motion and so is everything else on the galaxy. Thus, the the third person is moving at the same speed of the Earth.
This explains the fact the things move relative to each other. This is the basic concept of relativity. It is called Classical Relativity.
Along with these findings, Einstein put together the theories of Time Dilation, Length Contraction and Spacetime.
Time Dilation : Here, Einstein explains that time slows down for an objects travelling close to the speed of light and that it stops completely for an object revelling at the speed of light. This led to the conclusion that time travel would be possible if we succeeded in obtaining a speed greater that the speed of light. But it is difficult to achieve a speed greater than light due to the fact that the mass of an object increases as it approaches the speed of light and it would take an infinite amount of energy to do so.
Length Contraction : According to this concept, when objects move close to the speed of light, The object itself contracts along with the slowing down of time.
Thus, time dilation and length contraction work together top ensure that the speed to light remains uniform in all scenarios.
Spacetime : Einstein came to think of 3 dimensions of space and 1 dimension of time bound together as a fabric. He called it Spacetime. According to this concept, the fabric of spacetime is warped and stretched by heavy objects like planets and stars. And it is this warping of spacetime that creates what we experience as gravity. According to this phenomenon, the Earth rotates around the Sun simply because it follows the curves created on the spacetime fabric by the mass of the Sun.