"Version: 20180801"--Title page verso."A Morgan & Claypool publication as part of IOP Concise Physics"--Title page verso.Includes bibliographical references.1. Motivation and introduction -- 1.1. The four fundamental interactions -- 1.2. Particle exchange and force mediation -- 1.3. Examining a simple model -- 1.4. Relativity emerges -- 1.5. The necessity of fields and a conundrum -- 1.6. Exerc…