Jennifer Coopersmith.
The Lazy Universe: an introduction to the Principle of Least Action.
OUP. 2017
The Principle of Least Action is the ‘Harrison’s Chronometer’ of physics:
whatever the scenario and whatever the reference frame (a bit like wind-direction or choppy seas)
the Principle is the beacon that illuminates what’s really going on.
The book also explains where the Hamiltonian comes from, and what energy is.
The author draws from Cornelius Lanczos’s book “The Variational Principles of Mechanics” (1949 and 1970). Lanczos was a brilliant mathematician and educator, but his book was for a postgraduate audience. The present book is no mere copy with the difficult bits left out—it is original, and a popularization. It aims to explain ideas rather than achieve technical competence, and to show how Least Action leads into the whole of physics.