In physics, a unified field theory (UFT) is a type of field theory that allows all that is usually thought of as fundamental forces and elementary particles to be written in terms of a pair of physical and virtual fields. According to the modern discoveries in physics, forces are not transmitted directly between interacting objects but instead are described and interrupted by intermediary entities called fields. Classically, however, a duality of the fields is combined into a single physical field. For over a century, unified field theory has remained an open line of research and the term was coined by Albert Einstein, who attempted to unify his general theory of relativity with electromagnetism. The "Theory of Everything" and Grand Unified Theory are closely related to unified field theory, but differ by not requiring the basis of nature to be fields, and often by attempting to explain physical constants of nature. Earlier attempts based on classical physics are described in the article on classical unified field theories. The goal of a unified field theory has led to a great deal of progress for future theoretical physics, and progress continues. Introduction to the Great Theory Forces All four of the known fundamental forces are mediated by fields, which in the Standard Model of particle physics result from the exchange of gauge bosons. Specifically, the four fundamental interactions to be unified are: Strong interaction: the interaction responsible for holding quarks together to form hadrons, and holding neutrons and also protons together to form atomic nuclei. The exchange particle that mediates this force is the gluon. Electromagnetic interaction: the familiar interaction that acts on electrically charged particles. The photon is the exchange particle for this force. Weak interaction: a short-range interaction responsible for some forms of radioactivity, that acts on electrons, neutrinos, and quarks. It is mediated by the W and Z bosons. Gravitational interaction: a long-range attractive interaction that acts on all particles. The postulated exchange particle has been named the graviton. Modern unified field theory attempts to bring these four forces and matter together into a single framework. History Classic theory The first successful classical unified field theory was developed by James Clerk Maxwell. In 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