The basic fields of classical physics are mechanics and heat on the one hand and electromagnetism and optics on the other. Mechanical and heat phenomena involve the motion of particles as governed by Newton’s equations. Electromagnetism and optics deal with fields and waves, which are described by Maxwell’s equations. In the classical description of particle motion, the position of the particle is exactly determined at any given moment.Wave phenomena, in contrast, are characterized by interference patterns which extend over a certain region in space. The strict separation of particle and wave physics loses its meaning in atomic and subatomic processes.