Relationship between string theory and quantum field theory
Many first principles in quantum field theory are explained, or get further insight, in string theory. == From quantum field theory to string theory == Emission and absorption: one of the most basic building blocks of quantum field theory, is the notion that particles (such as electrons) can emit and absorb other particles (such as photons).
Source: Wikipedia — Relationship between string theory and quantum field theory (CC BY-SA 4.0)