Unified field theory 1820 Hans Christian Ørsted discovered that electric currents exerted forces on magnets, while in 1831, Michael Faraday made the observation that time-varying magnetic fields could induce electric currents. Until then, electricity and magnetism had been thought of as unrelated phenomena. In 1864, Maxwell published his famous paper on a dynamical theory of the electromagnetic field. This was the first example of a theory that was able to encompass previously separate field theories (namely electricity and magnetism) to provide a unifying theory of electromagnetism. By 1905, Albert Einstein had used the constancy of the speed of light in Maxwell's theory to
Field (physics) of jet manifolds (covariant classical field theory). In modern physics, the most often studied fields are those that model the four fundamental forces which one day may lead to the Unified Field Theory. A convenient way of classifying a field (classical or quantum) is by the symmetries it possesses. Physical symmetries are usually of two types: Fields are often classified by their behaviour under transformations of spacetime. The terms used in this classification are: Fields may have internal symmetries in addition to spacetime symmetries. In many situations, one needs fields which are a list of space-time scalars: (φ, φ, ...