Definitions for quantum field theory
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quantum field theory(noun)
the branch of quantum physics that is concerned with the theory of fields; it was motivated by the question of how an atom radiates light as its electrons jump from excited states
Quantum field theory
In theoretical physics, quantum field theory is a theoretical framework for constructing quantum mechanical models of subatomic particles in particle physics and quasiparticles in condensed matter physics, by treating a particle as an excited state of an underlying physical field. These excited states are called field quanta. For example, quantum electrodynamics has one electron field and one photon field, quantum chromodynamics has one field for each type of quark, and in condensed matter there is an atomic displacement field that gives rise to phonon particles. In QFT, interactions between particles in quantum mechanics are represented by interaction terms between the underlying fields. QFT interaction terms are similar in spirit to those between electric and magnetic fields in Maxwell's equations. However unlike the classical fields of Maxwell's theory, fields in QFT generally exist in quantum superpositions of states and obey the laws of quantum mechanics. Quantum mechanical systems have a fixed number of particles, with each particle having a small number of degrees of freedom. In contrast, the excited states of a QFT can represent any number of particles. This makes quantum field theories especially useful for describing systems where the particle count/number may change over time.
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"quantum field theory." Definitions.net. STANDS4 LLC, 2014. Web. 21 Aug. 2014. <http://www.definitions.net/definition/quantum field theory>.