With the acceptance of the electromagnetic theory of light only two general problems remained. One of these was that of luminiferous ether, a hypothetical medium suggested as the carrier of light waves, just as air or water carries sound waves . The ether was assumed to have some very unusual properties, e.g., being massless but having high elasticity. A number of experiments performed to give evidence of the ether, most notably by A.A Michelson in 1881 and by Michelson and E.W. Morley in 1887, failed to support ether hypothesis. With the publication of special theory of relativity in 1905 Albert Einstein, the ether was shown to be unnecessary to the electromagnetic theory. Much before Einstein it was considered that the velocity of light, like other material’s particle velocity, should depend on the relative motion between the observer and the source of light. However, experiments failed to disapprove the constancy of velocity of light to generate a new branch of physics. According to classical mechanics space and time are absolute and they are not interconnected.
This absolute nature is broken by relativity which generally starts that both space and time are a function of observer’s velocity as well as observables velocity. At high velocities both space and time combine to form space-time continuum.
The theory which deals with the relativity of motion and rest is called the theory of relativity. Einstein was the pioneer in this field and did a lot which helps us to decode the mysteries of the universe.
It has two parts :
Special Theory of Relativity. It deals with objects and system which are either moving at a constant speed with respect to one another or at rest.
General Theory of Relativity. It deals with objects and system which are speeding up or slowing down with respect to one another.
Here we are only dealing with Special Theory of Relativity only.