On the Origin of Time: Stephen Hawking's Final Theory

by Thomas Hertog

In November 1915, in the dark days of World War I, Einstein could finally put forward his theory of general relativity, a new theory of gravity, consistent with his special relativity theory of spacetime, that would become his most sweeping scientific accomplishment. General relativity describes gravity in geometric terms—the geometry, in fact, of spacetime itself.[6] The theory conceives of gravity as a manifestation of the curving and bending of the fabric of spacetime by mass and energy. For example, the theory holds that Earth moves around the sun not because there is a mysterious force acting over that vast distance, somehow pulling upon Earth, but because the mass of the sun slightly warps the shape of space in its vicinity. This warping creates a sort of valley that guides Earth (and the other planets) into nearly elliptical orbits around the sun. We can’t see this valley but we feel it—it’s gravity!