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

by Thomas Hertog

This equation isn’t difficult to read. On the right-hand side we have all the matter and energy in a region of spacetime, denoted by Tµv. The left side describes the geometry, Gµv, of that region. The equal sign in the middle is where the magic happens: It tells, with mathematical precision, how the geometry of spacetime on the left (Gµv) is tied to a given configuration of matter and energy (Tµv) on the right, and this relationship, Einstein’s theory says, is what we experience as gravity. Hence gravity doesn’t enter Einstein’s theory as an independent force. It rather emerges from the interplay between matter and the shape of spacetime. As the American physicist John Archibald Wheeler put it, “Matter tells spacetime how to curve. Spacetime tells matter how to move.”[7]