"How do objects and images move? Why do animals move? What is motion?
How does a rainbow form? Is levitation possible? Do time machines exist? What does 'quantum' mean? What is the maximum force value found in nature? Is 'empty space' really empty? Is the universe a set? Which problems in physics are still unsolved?
This site publishes a free physics textbook that tells the story of how it became possible, after 2500 years of exploration, to answer such questions. The book is written to be entertaining, surprising and challenging on every page. With little mathematics, the text explores the most fascinating parts of mechanics, thermodynamics, special and general relativity, electrodynamics, quantum theory and modern attempts at unification. The essence of these fields is summarized in the most simple terms: it is shown how they are based on the notions of minimum entropy, maximum speed, maximum force, minimum change of charge and minimum action."