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The theory of relativity, formulated by Albert Einstein, consists of two theories. First is the special theory of relativity, postulated in Einstein’s 1905 paper, and the second is the theory of general relativity, which was introduced in 1916. An overview of this topic is in the class 12th school curriculum and we have tried to familiarise students with this most crucial and fundamental idea of modern physics. This article will help them understand the theory of relativity, its facts and postulates in detail. So, let us start with the special theory of relativity.

The Special Theory of Relativity

Special theory of relativity, or special relativity, explains the relationship between space and time. The two main postulates of the Special theory of relativity are.

• The first postulate states that the law of physics is constant across all frames of reference.
• The second postulate states that the speed of light in a vacuum remains constant, irrespective of the movement of the observer.

Frame of Reference

The reference frame is the idea on which Einstein’s special theory is based. And it is nothing but the point at which a person is sitting or standing. As you are currently sitting in front of a computer, you might feel like you are stationary as you are not moving, but the earth on which you are sitting is revolving on its axis and rotating around the sun. This means you are moving in space and time. Also, as every single object in the universe is moving, you can’t make an object a base. So, if Rohan runs towards Rishi, there are two ways to look at it. For Rishi, Rohan is moving towards him, but for Rohan, Rishi is moving towards him. Let us discuss the two postulates of the special theory in detail for better understanding.

1. The first postulate of the special theory of relativity is not too difficult to understand. According to this postulate, the laws of physics, such as the law of motion and gravitational laws, remain consistent irrespective of the observer's reference frame and perspective. Let us take the case of a cement block. If you measure it while sitting on the bus (which is travelling at a constant velocity on a smooth road) or standing on the ground, the results will remain the same. However, if you measure the cement block as it passes you on the bus, you will get different results. The second postulate will help you understand why the results are different.

2. The second postulate is very interesting and unexpected because it says that the speed of light remains constant in all frames of reference. While our cement block is unrelated to the light, this postulate will change your understanding of measurements when two reference frames are involved. As the bus is in motion, its reference frame differs from the observer. According to the second postulate, the length and times of two frames of reference, which are in relative motion to each other, appear different. This phenomenon is called length contraction, in which an object appears shorter along the direction of motion.

General Theory of Relativity

Physicist John Wheeler summed up Albert Einstein's general theory of relativity as “Space-time tells matter how to move, and matter tells space- how to curve”.

The general theory of relativity is the fundamental building block of modern physics. This is because it helps us understand the theory of gravity. It was the extension of Einstein's special theory of relativity and took him around ten years to formulate from 1905 to 1916.

Einstein proposed that gravity is not just a pull between one object and another but the result of mass telling space and time how to curve and space and time instructing mass how to move. Let us say you put a heavy ball on the trampoline. This heavy ball creates a dent in the trampoline, and when you put a marble on the trampoline, it takes a curved path rather than a straight path. This principle helps physicists determine why small planets follow curved orbits rather than straight lines.

The theory also describes that time slows down in strong gravitational fields such as a massive planet and black holes. The theory also predicted many phenomena, such as gravitational waves, black holes, gravitational lensing, expansion of the universe, and many more.

Also Read: Understanding the Theory of Evolution.

Summary

The theory of relativity is considered one of the most successful theories and has helped formulate many theories afterwards. It describes the history of the universe and countless cosmic phenomena, such as weak fields and strong fields of gravitation. We hope this article will help you understand this topic in detail and encourage you to dive deep into the fascinating world of physics. Stay tuned to read more interesting blogs and articles.