Laws take the same form in every reference frame.
Define the infinitesimal distance between two points.
Contravariant, covariant vectors, invariant inner product.
Summation convention.
Examples of fields in Nature.
The four-dimensional Lagrangian.
The Action Principle in four dimensions.

1. Inertial Reference Frames
2. Principle of Least Action
3. Invariance of the Laws of Nature
4. Lagrangian Mechanics
5. Conservation of Charge and Momentum
6. Relativistic Wave Equation and Conservation Laws
7. Invariance under Gauge Transformations
8. Gauge Theory

This Stanford Continuing Studies course is the second of a six-quarter sequence of classes exploring the essential theoretical foundations of modern physics. The topics covered in this course focus on quantum mechanics. The course is taught by Leonard Susskind, the Felix Bloch Professor of Physics at Stanford University.