Lagrangian dynamics
The beauty of the action principle and variational calculus
Sometimes for me it is a matter of mystery or faith that the action principle can indeed encapsulate all the physical content of a theory. The action: a single scalar, made out of scalars, without which, nowadays, no theory is really trusted too much.
What does it mean that a physical theory must have a Lagrangian descrition? It is clear that not all second order differential equations come from a Lagrangian. Therefore, it looks like physics selects a tiny subclasses of possible dynamics.
Do you know Lagrange real name?
The action principle behind our world