Introduction

In earlier chapters, we introduced Lagrangian mechanics and briefly discussed the principle of least action. In this chapter, we explore this idea in greater depth.

Variational principles provide a powerful and unifying framework for physics. Instead of directly solving differential equations, we determine the motion of a system by finding a path that makes a certain quantity — the action — stationary.

This approach is fundamental in:

• Classical mechanics
• Quantum mechanics
• Field theory