This book is fiction, presented in the form of a discussion. Galileo, accompanied by the President of the session, Kepler, Newton, Einstein and No?, audition various experts over three days. They explore some thirty physical experiments and observations, from falling bodies to the cosmic microwave background, GPS and black holes. The aim of this book is to present Neo-Newtonian Mechanics as an alternative to the theory of Relativity. The structure of the dialogue enables a lively comparison of these two theories, which are richly illustrated with numerous diagrams. The discussions and debates also highlight the limitations of each theory. It's this exploration that I invite you to share with them.