Michael Stoeltzner (U South Carolina): “Model Choice and Crucial Tests. On the Empirical Epistemology of the Higgs Discovery.”

Abstract: To quite a few observers outside the field of elementary particle physics, the discovery of the Higgs boson in 2012 appeared to be just the final step in a long series of discoveries and precision tests in which stronger and stronger accelerator experiments had confirmed all particles of the Standard Model (SM) and scrutinized their interactions. The present paper argues that this picture needs qualifications. They provide two important lessons for the role of crucial experiments in a theory-laden context and the operation of epistemic and pragmatic criteria of theory (or model) choice.

On the basis of two broadly-spread questionnaires and two series of interviews with LHC physicists shortly before (autumn 2011) and shortly after (autumn 2012) the Higgs discovery, we defend the following theses. First, even shortly before the Higgs discovery a significant percentage of physicists raised concerns whether it would at all be found at the LHC and expressed preferences for other explanations of the particle masses. However, shortly after the discovery was announced, the majority believed that LHC would eventually succeed in distinguishing a SM Higgs particle from a more complicated Higgs sector. The initial measurements, although in agreement with a SM Higgs, still provided significant room for new physics beyond the SM; and alternative mechanisms of dynamical symmetry breaking had considerable aesthetic appeal. Second, this case suggests that criteria of theory choice should be understood as epistemic and pragmatic values that have to be specified and weighed in actual research practice and in accordance with the progress of a research program. Some of these values, among them naturalness or simplicity, may function as narratives and act on different levels without becoming too vague to be applied consistently by the scientific community. Third, the conviction of the particle physics community that the Higgs discovery was indeed a crucial experiment for the SM withstands philosophical scrutiny. For an experiment as complex as LHC cannot be properly understood without its embedding into a tradition of previous precision experiment and a set of reliable experimental strategies. These are crucial for keeping confirmational holism and theory-ladenness at bay. This result is in line with recent debates that have shown that it is difficult to find interesting examples of non-transient underdetermination.

Michael Stoeltzner is a Professor of Philosophy at the University of South Carolina.