In 1905 Albert Einstein purposed how measurement of time and space are affected by motion between an observer and the object that is being observed. He called this theory the theory of Relativity and there are Special theory of relativity and General theory of relativity and both theories were worked out by Einstein. We will talk about Special theory of relativity today.

Special relativity states that All motions is relative; the speed of light in free space is the same for all observers.

There are few things we need to understand before we dive into special relativity. Firstly, what do we mean by motion? Motion is defined as change in an object’s position relative to something else. For example, an airplane moves relative to the earth, our sun moves relative to our galaxy etc. In each case we can see that the frame of reference is a something which is a part of the description of the motion.

An inertial frame of reference is one where Newton’s first law of motion holds true that is an object at rest remains at rest and object in motion will continue to be in motion at constant velocity of no force is acted upon it. You must have noticed that when you are in a bus or train the trees in the distance seems to move with respect to us. So, the question arises is it moving or we are moving? A relative motion is hard to grasp and understand. It is to be noted here that there is no universal frame of reference that can be used everywhere. Hence special theory of relativity deals with this lack of universal frame of reference and problems that involves inertial frames of reference. General relativity on the other hand deals with accelerated frame of reference with one another.

Postulates of Special Relativity

1. The laws of Physics are the same in all inertial frame of reference. (this postulates arises from the absence of universal frame of reference)
2. The speed of light in free space has the same value in all inertial frame of reference.