Quantum field theory (QFT) is a theoretical framework that unifies classical field theory, special relativity, and quantum mechanics by treating fields — rather than particles — as the fundamental entities that permeate spacetime, with particles reinterpreted as localized excitations (quanta) of their underlying fields; particle creation and annihilation correspond to the appearance and disappearance of such field excitations. QFT arose to resolve the negative-energy and particle-number instabilities of earlier relativistic quantum equations (the Klein–Gordon and Dirac equations), which attempted but failed to consistently reconcile special relativity with quantum mechanics. It belongs to theoretical physics, sitting between and unifying relativistic quantum mechanics and classical field theory, and is considered a partial step toward a more complete "theory of everything" (excluding general relativity/gravity).
Quantum field theory (QFT) is a theoretical framework that unifies classical field theory, special relativity, and quantum mechanics by treating fields — rather than particles — as the fundamental en…