Quantum field theory (QFT) is a powerful language for describing the subatomic constituents of the physical world (quarks, leptons, gauge bosons, Higgs scalars, and so on) and the laws and principles that govern them. Not only has it provided a framework for understanding the hierarchical structure that can be built from these constituents, it has also profoundly influenced the development of contemporary cosmology and deeply penetrated into the current conception and imagination of the origin and evolution of the universe. For this reason, it has justifiably long been taken to be the foundation of fundamental physics: elementary particle physics and cosmology.

QFT reached its most spectacular success in the early 1970s in the standard model, which is able to describe the fundamental interactions of nature within a unified theoretical structure: the non-Abelian gauge theory. Ironically enough, however, this success brought about a long period of stagnation in its conceptual development: virtually nothing of physical importance occurred after the construction of the standard model except for its detailed experimental verification. This situation can be assessed in different ways, depending on what perspective we start with. For example, the stagnation could be taken to be an indication that the theoretical development of fundamental physics has come to an end.