The Twilight of Falsification? Muon Physics and the Limits of Experimentation

In this talk, I aim to explore a fundamental shift in the theory-experiment relationship in high-energy physics, using historical examples from muon studies. By examining the trajectory from Anderson and Neddermeyer’s discovery of the muon in cosmic radiation to the ongoing anomalous muon magnetic moment measurements by the g-2 experiment at Fermilab, I highlight critical changes in the role of theory in guiding experimental interpretation. In the former case, the identification of the muon as a new particle was facilitated by a shift in theoretical perception. Initially, the curved particle tracks observed in cloud chambers were seen as familiar electrons until Yukawa’s theoretical concept of a heavy lepton opened the way to recognizing these tracks as muons. Here, theory drove interpretation, leading to the discovery of new phenomena. In contrast, the recent g-2 experiment at Fermilab, aimed at detecting an anomalous muon magnetic moment initially predicted by beyond Standard Model (BSM) theories, was ultimately reconciled with refined SM calculations, reducing the result to a mere confirmation of the Standard Model. This calls into question the theoretical significance of contemporary high-energy physics (HEP) experiments, as they now confirm rather than challenge numerous existing frameworks. In this talk, I will discuss the growing theoretical ambivalence surrounding HEP experiments, focusing on the tendency of theoretical predictions to degenerate or adjust retroactively. This trend calls for prioritizing robust, falsifiable theoretical work over costly experimental facilities before large-scale experiments.