Climbing the Cosmic Distance Ladder

This dissertation is a philosophical and historical study of the development of modern cosmic distance measurement, particularly during a period known as the 50-or-100 debate, from approximately the 1960s until 2000. Each chapter focuses on a strategy for building confidence in distance measurements during this period, chosen both for their philosophical interest and relevance to modern debates over the cosmic distance scale. Chapter 2 examines the challenge of constructing classification schemes that identify standard distance indicators. In particular, I focus on three distance indicators---type Ia supernovae, spiral galaxy luminosity classes, and H II region diameters---and argue that differences in the classification schemes are relevant to the success or failure in each case. Chapter 3 traces the evolution of type Ia supernovae from their use as standard candles to their reconceptualization as standardizable candles. I examine how the standardness of these objects was evaluated absent pre-existing standards. I argue that assumptions about the standardness of these objects were often built into studies of their standardness. Chapter 4 explores the role of multiple measurements, robustness, and consilience in the debate. In particular, I assess two methods developed for constructing and testing distance ladders with multiple measurements: Gérard de Vaucouleurs's spreading the risks method and Allan Sandage and Gustav Tammann's precision indicators method. I argue that these methods were not different views on the best way to incorporate multiple lines of evidence into a distance ladder in general, but reflected the participants' differing views on the quality and trustworthiness of available indicators and models. Chapter 5 assesses the use of cosmological models in the debate, highlighting varying views among participants regarding the role cosmological modeling should play in cosmic distance measurement. As a case study, I examine connections between the age of the universe and the distance scale.