##### Basic Science

# How Einstein Discovered Theory of Relativity

**What is Theory of Special relativity and how Einstein discovered this theory?**

Time, you can’t see it, you can’t hear it, but experience it. Every moment the whole piece of time is a landscape and we forward slice by slice but do we really understand time. Is time same for everyone? To understand time, let’s go back in time and make a small journey with Albert Einstein. Yes he was who helped us to understand the time by giving his theory of special relativity. But the more fascinating is that how he discovered the theory of relativity?

To understand let’s go back to time. Einstein used to work for patent and published his paper on round and motion and existence of Atom. But these theories did not give him that name and fame which he deserved as a physicist. And this did not stop Einstein from researching. In his childhood he used to think how world would look like if he travel by sitting on the light. These types of questions brought curiosity in his mind.

Now, To understand the theory of relativity. First we have to understand the frame of reference and also how motion is relative and the most importantly, we also have to understand that time is relative not absolute. Let’s understand in detail, the theory of relativity is valid for inertial frame of reference. There are two types of references. One is inertial frame of reference and other is non inertial frame of reference. Interial frame of reference is that reference in which body moves with a constant velocity or body is in rest. Where the non inertial frame of reference is that in which body accelerates means whose velocity changes with time.

Let’s understand how motion is a relative term. Suppose a car is moving west to east with the speed of 60km/hr. And in the car two boys are sitting and a girl is standing on the road who is observing the car. According to those boys, they are in the rest and world outside the car is in motion and for them girl is moving east to west(means opposite to them) with the speed of 60km/hr. Where according to the girl, boys are moving west to east with speed of 60km/hr means in the direction of speed of car and she is in rest because she is not moving. So now you think according to the boys, girl is in motion where as according to the girl, boys are in motion. So who is right here. Actually both are right because motion is a relative term. If we want to know body is in motion or rest then we should first have to know in which respect or in whose frame of reference we are talking.

Einstein worked on these types of thought experiments and got to know that motion is a relative term. But Einstein faced the problem when he got to know that speed of light is constant and light has fixed speed. Einstein felt this problem and on the basis of which he laid the foundation of theory of relativity.

Let’s understand what problem did Einstein faced with the help of a thought experiment, suppose there is a car moving with the speed of 60km/hr and a boy is standing on the car who has a ball in his hand and on the other side a girl is observing the car, now suppose the boy throws the ball with the speed of 20km/hr in the direction of car. So according to the boy the speed of the ball is 20km/hr but according to the girl, speed of ball would be 80km/hr. This is because of relative motion. But now suppose that boy has a flashlight in his hand instead of ball and he switches the flash light on in the direction of car. Then according to the boy the speed of flashlight will be equal to speed of light and according to the girl it will be speed of car plus speed of light. But if this happens, then the speed of light is not constant means it has no fixed value. But we already know that speed of light is constant. So something is missing here. So Einstein faced this problem and tried to solve it. He argued that speed of light is constant and nothing can travel faster than it. So if speed of light is same for all frame of references means speed of light would have to be same from the viewpoint of the boy as well as the girl. He also argued that time and distance vary to maintain the speed of light constant.

As we know, speed = distance/time

If we want to make speed constant then we have to change the distance and time. He explained it more conspicuously through length contraction and time dialation. So he argued that if body moves with a high speed nearly with the speed of light then its time slows down. As time is relative not absolute. That will happen because when the boy moves faster and faster so to make that speed constant, time will slow down. So in this way, if a body nearly moves with the speed of light, then the length of the body contracts so that speed of light does not break. And this is what we call length contraction. This means that time moves differently for everyone. If a body is in motion then its time moves in a different way and if a body is in rest then its time moves differently. So time is neither constant nor absolute but relative. It means in this universe everything is not happening simultaneously because time is different for everything.

So on the basis of this thought, Einstein gave the birth to the theory of special relativity. This theory led to many other invaluable findings, the most of which is the equation E=mc^2. After all this he got so much name and fame which he really deserves. This theory brought new thoughts in physical science and changed the perspective of many things.