1. Introduction

The Theory of Relativity was developed by a famous German physicist, Albert Einstein in early 1900's. The theory of relativity is comprised of two interrelated theories of relativity. The first is Special theory of Relativity and the second is General theory of Relativity. Special theory of relativity applies to all physical phenomena in the absence of gravitation. Whereas the General theory of relativity explains the law of gravitational and its relation to other forces of nature.

The theory aims to solve problems which could not be solved by classical physics or by 19^th century physics. Certain observations or events occurs in Universe cannot be explained by the physics of 1900. Einstein set out to revise the basic ideas of physics. It introduced concepts including space-time as a unified entity of space and time, relativity of simultaneity, kinematic and gravitational time dilation and length contraction. With the relativity theory, cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes and gravitational waves.