Walter Thirring 
Course in Mathematical Physics 1 and 2 [PDF ebook] 
Classical Dynamical Systems and Classical Field Theory

The last decade has seen a considerable renaissance in the realm of classical dynamical systems, and many things that may have appeared mathematically overly sophisticated at the time of the first appearance of this textbook have since become the everyday tools of working physicists. This new edition is intended to take this development into account. I have also tried to make the book more readable and to eradicate errors. Since the first edition already contained plenty of material for a one- semester course, new material was added only when some of the original could be dropped or simplified. Even so, it was necessary to expand the chap- ter with the proof of the K-A-M Theorem to make allowances for the cur- rent trend in physics. This involved not only the use of more refined mathe- matical tools, but also a reevaluation of the word "fundamental. " What was earlier dismissed as a grubby calculation is now seen as the consequence of a deep principle. Even Kepler’s laws, which determine the radii of the planetary orbits, and which used to be passed over in silence as mystical nonsense, seem to point the way to a truth unattainable by superficial observation: The ratios of the radii of Platonic solids to the radii of inscribed Platonic solids are irrational, but satisfy algebraic equations of lower order.