What is Einstein's Theory of Relativity

If you were asked to stand in the hot sun, in a line for purchasing tickets for a game or a movie, it would seem like ages before you get the tickets! On the other hand, if you were actually inside a movie theater, time would simply fly and before you finish the popcorn, half the story would be over! Even if the duration for which you were in the line and inside the cinema hall, were the same, the former would seem much longer. This is somewhat similar to what Albert Einstein attempted to explain through his theory of relativity. In the above example, the same time period appears to be different and hence, said to be a relative concept and not an absolute parameter. When research papers were first published with the theory, it was claimed that only about a dozen people in the world could understand this theory.

The Theory of Relativity

Albert Einstein's theory of relativity consists of two parts, general relativity and special relativity. The special relativity theory was first proposed and explained by Einstein in 1905. Though the term was actually coined and used by Galileo in the 1600s, his versions had several flaws. Einstein's theory is about space-time and its components based on two basic postulates.

First postulate

Every body which is in uniform motion, is governed by the same laws of physics, relative to one another. Motion is a relative concept and can only be measured relative to something else. When you say, 'this car is fast' or 'the athlete is a bit slow', it is a comparison of these entities with some other standard but stated incompletely. The complete form would be something like, 'this car is fast in relation to that car' or 'the athlete is a bit slow as compared to the other'. There is no absolute standard which states that a speed above or below a certain mark is defined as high or low. Thus, a body in motion cannot in itself, give an idea about its speed. It is only when its speed is considered relative to another parameter, can its speed be measured.

If you are traveling in a train, for a person sitting next to you or in front of you, both of you are stationary. This is because the both of you are moving with the same relative motion, hence, according to him your speed is zero. But for a person standing outside the train, your relative speed will be the same as the speed of the train.

Second Postulate

The second law states that, 'The speed of light in a vacuum is the same for all the observers or independent of the movement of either the light source or the observer in concern'. This means that the only absolute factor in the universal scheme of things is the speed of light in vacuum or the speed of light. The speed of light is roughly calculated to be 186,000 miles per second. According to Einstein's theory, any body moving at this speed would be in an absolute state relative to any observer, whether moving or standing.

In the previous example, let us consider a situation where the train is moving at 60 miles per hour. Normally, for a stationary observer you are moving at a speed of 60 miles per hour. If another person is moving alongside the train, at a speed of 20 miles per hour (again, this is speed relative to the stationary person), your speed relative to his would be 40 miles per hour. Similarly, if he moves in the opposite direction of the train, your speed would be 80 miles per hour. But according to the second law, if you assume that the train moves at the speed of light, its speed would be the same for a stationary observer or a person traveling alongside in either direction.

Based on these, two statements, Einstein derived some other principles like relative simultaneity, length contraction, time dilation or the famous Einstein energy mass relation, E=mc².

The complete significance of this theory can only be realized by a detailed study of the associated sciences. Einstein's theory of relativity has led to many astounding discoveries and inventions that have helped mankind enormously.