Lorentz Transformation: The postulate of STR is proposed by Einstein in 1905. The two postulates are:
1. Principle of equivalence: According to this "The laws of physics are the same in all inertial frame of references moving with a uniform velocity with respect to one another". Law that hold for one frame of reference cannot be violated for any other inertial observer.
2. Principle of constancy of speed of light: The speed of light in free space is absolute. The value of speed of light is a universal constant and does not depend on the motion of observer and object, it is also independent of direction of motion.