Our understanding of nature's deepest reality has changed radically, but almost without our noticing, over the past 25 years. Transcending the clash of older ideas about matter and space, acclaimed physicist Frank Wilczek explains a remarkable new discovery: matter is built from almost weightless units, and pure energy is the ultimate source of mass. He calls it "The Lightness of Being." Space is no mere container, empty and passive. It is a dynamic grid, modern ether, and its spontaneous activity creates and destroys particles. This new understanding of mass explains the puzzling feebleness of gravity, and a gorgeous unification of all the forces comes sharply into focus. The Lightness of Being is the first book to explore the implications of these revolutionary ideas about mass, energy, and the nature of empty space. In it, Wilczek masterfully presents new perspectives on our incredible universe and envisions a new golden age of fundamental physics.