Representing the Unobservable

Markus Ehberger studied physics (B.Sc.) and history of science (M.Sc.) in Regensburg and Jena. He was a member of the DFG-funded research group The Epistemology of the LHC in the project A1: The Formation and Development of the Concept of the Virtual Particle. Within this project, he was a research associate at the TU Berlin and the RWTH Aachen and wrote his dissertation (TU Berlin) about the conceptual development of the virtual particle. As a research associate at FSU Jena and together with Christian Forstner, he developed and wrote a physics history city guide for the city of Jena. Since 2022, Markus Ehberger has worked at the Deutsches Museum (Munich), at first as the Managing Editor of the Open Access book series Deutsches Museum Studies, now as part of the internet editorial office and as a member of the team for the new physics exhibition.

• Chapter 1. Introduction.- Chapter 2. How to conceive of the concept of virtual particles in a historical study of its development.- Chapter 3. The community of practitioners.- Part I. From virtual oscillators to virtual transitions (1923–1929).- Chapter 4. The BKS theory and the Light Quantum Hypothesis: virtual entities and transitions to intermediate states, but in different conceptual frameworks (1923–1925).- Chapter 5. Dirac’s verbal model: Making transitions a quantum concept (1927).- Chapter 6. The Raman effect: How virtual transitions became “virtual” (for the first time) and real transitions were excluded from the conception of scattering (1928–1929).- Part II. Theoretical practice with virtual transitions (1928–1942).- Chapter 7. Scattering and the sea: Antiparticles and intermediate states (1928–1931).- Chapter 8. The practice of time-dependent perturbation theory (Part I): Formal and conceptual extensions (1929–1936).- Chapter 9 The practice of time-dependent perturbation theory (Part II): Virtual possibilities, modes of representation, and the reprise of the “Schüttelwirkung” (1934–1942).- Part III. From virtual transitions to virtual particles (1930–1949).- Chapter 10. In between: Traces of the virtual particle during the 1930s.- Chapter 11. Outlook: Feynman, diagrams, and virtual particles (1948–1949).- Part IV. Analysis, Summary, and Conclusion.- Chapter 12. Representations and Practices in the Formation of the Virtual Particle Concept.