# Famous Theories

by Albert Einstein

## Theory Of Relativity

One of the greatest contributions of Einstein was the development of the theory of relativity, which refers to two theories: special relativity and general relativity.

### Special Relativity

The theory of special relativity was introduced by Einstein in a paper published in 1905, titled “ On the Electrodynamics of Moving Bodies ”. It sought to explain the structure of spacetime. Special relativity is based on two contradictory postulates in classical mechanics, which are:

- The laws of physics are the same for all observers in uniform motion relative to one another.
- The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light.

He produced E = mc^{2} from his special relativity equations which express the fact that mass and energy are the same physical entity and can be changed into each other.

### General Relativity

General relativity is a theory of gravitation developed by Einstein in 1907-1915. He developed the equivalence principle, which became the basis of general relativity. Equivalence principle stated that the states of accelerated motion and being at rest in a gravitational field are physically identical. This led to the assumption that an object in free fall is falling since no force is exerted upon it, instead of the force of gravity as believed by classical mechanics.

This assumption was incompatible with classical mechanics and special relativity, which put forward that inertially moving objects cannot accelerate with respect to each other, though objects in free fall do so. To resolve this contradiction, Einstein devised field equations which relate the curvature of spacetime with the mass, energy, and momentum within it. Some observations of general relativity are as follows:

- Time goes more slowly in higher gravitational fields. This is called gravitational time dilation.
- Rays of light bend in the presence of a gravitational field.

## Quantum Theory

The quantum theory developed by Einstein lays down that energy and some other physical properties often exist in very tiny, discrete amounts. Together, the Quantum theory and theory of Relativity form the basis of modern physics. Einstein's contemporaries also elaborated on this theory by adding new dynamics to it. By the 1930’s, Einstein accepted quantum mechanics as a consistent theory for the statistics of the behaviour of atoms, though he could not accept it as a complete theory.