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Question 1.10
Describe the concept of a field. Briefly outline the history of this concept from the time of Faraday to the present day.

A field is a physical quantity with a value at each point in space. A particle passing through a given point will experience forces that depend on the fields at that point. Thus the concept of a field replaces action at a distance.

Faraday introduced fields in the context of magnetism and electricity, and Maxwell established the reality of these fields by showing that wave-like disturbances of electric and magnetic fields can travel through space at the speed of light. He interpreted light as an electromagnetic wave and predicted the existence of longer wavelength electromagnetic waves (radio waves). Einstein's general theory of relativity is a field theory of gravitation in which the field describes the curvature of space-time.

A quantum theory of fields was developed which incorporates ideas from quantum mechanics and special relativity. Quantum electrodynamics is an example of a quantum field theory, in which the electromagnetic field is quantized and the quanta are photons. Quantum field theory also applies to ordinary matter - there are electron fields for example, with the quanta interpreted as the electrons. In quantum field theory, quanta may be created or destroyed as the field becomes more or less excited.

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