The laws of physics are the same in any inertial reference frame.

The Lorentz transformation is the transformation between two inertial frames.

Galilean transformation is appropriate for small velocities.

Proper time is the time an observer measures with a clock traveling with the observer, and is an invariant under a Lorentz transformation.

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.