Virtuality in modern physics in the 1920s and 1930s: Meaning(s) of an emerging notion

This article discusses the meaning of the notion of virtuality in modern physics. To this end, it develops considerations on the introduction and establishment in nuclear physics of two independent concepts at the turn of the 1920s and 1930s: that of the virtual state, used in the context of neutron scattering studies, and that of the virtual transition, useful for the theoretical understanding of strong nuclear forces, which forms the basis of what are now called virtual particles. Their comparative analysis highlights the theoretical nature of virtual entities and processes in modern physics. It also shows how the virtual has been associated with various purely physical attributes, leading to a form of polysemy of the term, from the beginning of the application of these concepts.