The first half of the 20th century brought a revolutionary change into our concept about space and time. Earlier it was thought that space and time were having independent existence, and that they were absolute. Even if all the matter disappeared from the universe, space would remain the same and unaffected. Similar view was held about time also, that time flowed in the same way throughout the universe and that this flow did not depend on anything. But with the coming of Einstein’s theory of relativity our concept about space and time has undergone a total and drastic change.