In the first part of this book, we employed classical physics to explain various aspects of light. Classical physics relies on two fundamental concepts: the notion of a particle, a discrete entity with a well-defined position and momentum governed by Newton’s laws of motion, and the concept of an electromagnetic wave, an extended physical entity with a presence at every point in space, characterized by electric and magnetic fields evolving according to Maxwell’s laws of electromagnetism. This classical framework offers an orderly description: particle motion laws account for the material world, whereas electromagnetic field laws explain the behavior of light waves that illuminate our surroundings.