From dressed electrons to quasiparticles: The emergence of emergent entities in quantum field theory

• We historicize debates about reduction and emergence in physics.
• We discuss the history of renormalization methods in QED and in many-body physics.
• Both cases prominently involved the introduction of emergent entities.
• Already before the 1970s, renormalization thus underwent a shift in interpretation.
• This shift involved a nontrivial interplay of empirical knowledge and theory.

In the 1970s, the reinterpretation of renormalization group techniques in terms of effective field theories and their subsequent rapid development led to a major reinterpretation of the entire renormalization program, originally formulated in the late 1940s within quantum electrodynamics (QED). A more gradual shift in its interpretation, however, occurred already in the early-to-mid-1950s when renormalization techniques were transferred to solid-state and nuclear physics and helped establish the notion of effective or quasi-particles, emergent entities that are not to be found in the original, microscopic description of the theory. We study how the methods of QED, when applied in different contexts, gave rise to this ontological reinterpretation.