Why the force that keeps our feet on the ground holds the key to understanding the nature of time and the origin of the universe. Gravity is the weakest force in the everyday world yet it is the strongest force in the universe. It was the first force to be recognized and described yet it is the least understood. It is a "force" that keeps your feet on the ground yet no such force actually exists. Gravity, to steal the words of Winston Churchill, is "a riddle, wrapped in a mystery, inside an enigma." And penetrating that enigma promises to answer the biggest questions in science: what is space? What is time? What is the universe? And where did it all come from? Award-winning writer Marcus Chown takes us on an unforgettable journey from the recognition of the "force" of gravity in 1666 to the discovery of gravitational waves in 2015. And, as we stand on the brink of a seismic revolution in our worldview, he brings us up to speed on the greatest challenge ever to confront physics.