The principle of least action originates in the idea that, if nature has a purpose, it should follow a minimum or critical path. This simple principle, and its variants and generalizations, applies to optics, mechanics, electromagnetism, relativity, and quantum mechanics, and provides an essential guide to understanding the beauty of physics. This unique text provides an accessible introduction to the action principle across these various fields of physics, and examines its history and fun...

Transitions to upper secondary education are crucial to understanding social inequalities. In most European countries, it is at this moment when students are separated into different tracks and faced with a ‘real choice’ in relation to their educational trajectory.Based on a qualitative driven approach with multiple research techniques, including documentary analysis, questionnaires and over 100 interviews with policymakers, teachers and young people in Barcelona and Madrid, this b...