Classical field theory

In a physical system consisting of a large number of particles, the interaction of the particles can be described with the aid of a concept of a field of force (electromagnetic or gravitational). The particle is assumed to create a field around itself and a certain force then acts on every other particle located in this field. As a consequence of the theory of relativity the field itself acquires a physical reality since particles at a distance from one another cannot be said to interact directly. A particle must first interact with the field which subsequently interacts with other particles.