Evidence and Confirmation in Precision Cosmology: The Case of the Accelerating Universe

This dissertation is on the philosophy of scientific experimentation, which is a relatively recent branch of philosophy of science that aims to understand what roles experiment play in the production of scientific knowledge and through what epistemic means experimental results are justified. I raise these questions in the context of experimental cosmology, and more specifically, I focus on the discovery of the acceleration of the rate of expansion of the universe as a case study. In the first two chapters, I provide a comprehensive historical account of the early empirical cosmology, and document the development of research on supernovae, and the employment of these objects as cosmological “tools.” Next, I study the specific histories of the High-z and the SCP teams, including their formation, approaches to the problem, and techniques for arriving at the final result. The remaining chapters undertake an epistemological analysis of the experiment. I first study two influential accounts of experimental knowledge, namely Franklin’s Bayesian epistemology of experiment and Mayo’s frequentist error-statistical philosophy. On the basis of the study of these two accounts, I identify a specific view on experimental confirmation that I refer to as the singularity thesis. According to the singularity thesis, all episodes of experimental confirmation need to include at least one decisive experiment. I argue that whereas Franklin’s account allows for the possibility of non-singular confirmation, Mayo’s severity requirement commits her to the singularity thesis. I conclude this chapter arguing that the confirmation of the expansion of the universe constitutes a counter–example to the singularity thesis, and claim that a non-singular account of experimental confirmation is needed in order to understand empirical justification in cosmology. The final two chapters offer such an account. Here, borrowing the key concepts of an exploratory experiment from Steinle, and epistemic iteration from Chang, I argue that experimental results are validated in cosmology through setting up a measurement protocol. I show that, in the case of the discovery of the accelerating universe, scientists formed a measurement protocol out of exploratory procedures in an iterative fashion, and sought a robust consistency of several measurements in order to confirm the result