ABSTRACT
U nderstanding the harmonic oscillator is the key to understanding physics. In fact, it is no exaggeration to say that you understand 90%
of physics if you understand the classical harmonic oscillator, and 99% of physics if you understand the quantum harmonic oscillator. This is because nature abounds in such examples-from the simple pendulum to LCR circuits. Collective excitations like normal modes or phonons in a solid obey the harmonic oscillator equation of motion. Perhaps the most important reason is that it is the first step in understanding light. A light wave is like a harmonic oscillator, except that instead of position and velocity oscillating (out of phase) as in a normal oscillator, it is the electric and magnetic fields that oscillate in a light wave. It is called a wave only because the disturbance propagates in some direction, but orthogonal to this direction the fields just oscillate in time. This chapter, therefore, deals with the harmonic oscillator and radiation, both classical and quantized. The radiation part will be of use in Chapter 6, “Interaction.”
