Albert Einstein felt the strong need to affirm Galilean relativity, which applied only to mechanical laws, that he decided to extend it to include electromagnetic and optical laws. He adopted the principle that no physical experiment (mechanical, optical, electromagnetic, or any physical law whatsoever) can distinguish between a state of absolute rest and a state of constant velocity. With the help of the German mathematician Herman Minkowski (who taught us to think in terms of spacetime rather than space and time individually. Einstein introduced a new principle of relativity and revolutionized mechanics.
There are two postulates of special relativity but the consequences are profound.
- Postulate 1 (Principle of Relativity): The laws of nature are the same in all inertial frames.
- Postulate 2 (Constancy of the Velocity of Light): The speed of light in empty space is an absolute constant of nature and is independent of the motion of the emitting body.
The entire edifice of special relativity follows by logical deduction from these two postulates. The only other assumptions required are that space is homogeneous (no region of space is intrinsically different from any other) and isotropic (there are no preferred directions in space.)