What is reality? Do space and time really exist when we set out to explore the most elementary foundations of our existence? How much of it can we even understand? Carlo Rovelli has been working for many years to expand the limits of our understanding. In this book, he takes us on a journey that leads from the understanding of reality in Greek classicism to loop quantum gravity. A great physicist of our time sets out to draw us a new picture of the world: with a physical universe without time, a space-time consisting of loops and grains, in which infinity does not exist. A cosmology that gets by without the big bang and parallel universes and which is explained here for the first time by one of its "inventors" in a simple and detailed way for a broad audience. A book about "the great challenges of the