This site provides 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 for the curious: it is entertaining, surprising and challenging on every page. With little mathematics, starting from observations of everyday life, 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. For example, the text presents modern physics as consequence of the notions of minimum entropy, maximum speed, maximum force, minimum change of charge and minimum action.
To enjoy curiosity even more, for each field of physics, the text presents the latest research results, the best animations, the best images, the most interesting physical puzzles and the most telling physical curiosities. It includes more than 500 animations and illustrations, 90 tables and 1600 challenges and puzzles.
Written in English, over 1300 pages are provided for students, teachers, and for anybody who is curious about the precise description of nature. To satisfy even the most extreme curiosity, the text ends by exploring the limits of time and space, and the wonders that can be discovered there.Download the text (20th edition, January 2007).
Cool, huh? Here are some sample entries from the mainpage:
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?