Theory of Time

Time and space were defined by the early classical science creators. They predicted all their experiences related to time and space in and around their own environ. Measurements with rulers and rods even before that were the foremost of all the measurement types. Motion of the bodies and the ancient clocks for calculating time, were the initial attempts. Galilean reference frame was used as a pivotal point of reference to arrive at further predictions.
This basic principle of relativity with the laws, based on a reference frame, was again reinstated by the findings of Einstein later on. Specific theory of relativity was put forth for the very first time by Einstein. It was the second postulate of Einstein, which brought in controversial opinions to the earlier finders of the classical theory of science.
Light has constant speed regardless of any point of reference frame said Einstein? It was accepted by the whole world and it is being followed in practice all until now with the speed of light being assumed as a constant as per the formula,
E= mc2