What is time? Does it exist? Can it be stopped? Can time's arrow be reversed? Can we ever free ourselves from the seemingly inexorable flow of time? Chronos is a mystery, and not only for us: it was a mystery for our distant ancestors too. In this book, Guido Tonelli guides us along the path to understanding a reality that is very different from what we believe it to be. Modern science allows us to explore the deepest recesses of the universe, and when we observe the giant objects which inhabit the cosmos over great distances – galaxies and clusters of galaxies – time acquires characteristics which are very different from those that we are used to. The same happens when we analyse the phenomena which occur on a sub-nuclear scale. In these two worlds which are so far apart from one other, the harmonious and constant flow of time which has enchanted us for millennia twists, melts and shatters. Space and time appear as an indissoluble couple – not some abstract concept but a material substance which occupies the entire universe, which vibrates, oscillates and is in a constant process of change. With Tonelli's erudite assistance, we discover the long history of time, its violent birth and strange evolution. In our imaginations, we travel to terrifying places where time stops and explore the close link which binds time to energy. This is a bewildering journey that forces us to discard our preconceptions and abandon all certainty, a journey in which myth, art and philosophy will come to our aid when our minds begin to falter.