What are the elementary ingredients of the world? Do time and space exist? And what exactly is reality? In elegant and accessible prose, theoretical physicist Carlo Rovelli leads us on a wondrous journey from Democritus to Einstein, from Michael Faraday to gravitational waves, and from classical physics to his own work in quantum gravity. As he shows us how the idea of reality has evolved over time, Rovelli offers deeper explanations of the theories he introduced so concisely in Seven Brief Lessons on Physics. Rovelli invites us to imagine a marvelous world where space breaks up into tiny grains, time disappears at the smallest scales, and black holes are waiting to explode—a vast universe still largely undiscovered.