General relativity and quantum mechanics were the two major breakthroughs that revolutionized theoretical physics in the twentieth century. General relativity gives the idea to understand the large-scale expansion of the Universe and gives a small correction to the predictions of Newtonian gravity for the motion of planets and the deflection of light rays, and it predicts the existence of gravitational radiation and black holes. It describes the gravitational force in terms of the curvature of spacetime which has fundamentally changed our view of space and time i.e. they are now viewed as dynamical.