In physics, a field is an assignment of a quantity to every point in space.

Physicists distinguish among three types of fields, which are, in increasing generality, as follows:

• scalar fields, such as temperature
• vector fields, such as the magnitude and direction of the force at each point in a magnetic field
• tensor fields, such as the stress-energy tensor in general relativity

Classically, field theory was first used to describe the behavior of particles in electric and magnetic fields. These were later unified into a single electromagnetic field, though the fields are still introduced separately when the subjects are being taught.

Another more recent change is the idea of energy being stored in a field. For example the convention used to be that when an object (say a book) had potential energy (the book being held up at a given height) that the energy of the situation was 'stored' in the object. The convention now holds that the energy is in the field acting on the object (the gravitational field of the Earth).

The quantum mechanical analogue of field theory is called quantum field theory. Examples of quantum field theories include:

• quantum electrodynamics
• quantum chromodynamics
• electroweak force

See also

• Field equation
• Coherent state
• Gauge theory

Electronics

• Closed waveguide
• Electric field
• Electromagnetic radiation hazard
• Far-field region
• Flux
• Fresnel zone
• Magneto-optic effect
• Mode field diameter
• Near-field region
• Speckle pattern
• Surface wave