Evidential Reconfiguration as Bayesian Confirmation For Dark Matter in 1974: How Existing Data Become Evidence in New Structures

Abstract

The 1974 papers by Ostriker et al. [1974] and Einasto et al. [1974] are considered by many to be pivotal in establishing the epistemic foundations for the dark matter hypothesis. From a theory confirmation point of view, the circumstances surrounding this pivot are difficult to reconcile with common approaches to epistemic support. First, the papers did not introduce any new observations. Second, they synthesized existing data from two separate contexts to construct a hypothesis under which the joint data became evidentially relevant. Third, this synthesis was motivated in part by non-empirical reasons. The situation excludes both temporal novelty and use novelty because already known data was used in the construction of the hypothesis. Yet, the papers are widely regarded as epistemically transformative. I argue that a Bayesian can model the epistemic significance of the 1974 papers without concession. By recognizing how the papers reconfigured the existing data to bear on a missing mass hypothesis, a novel epistemic aspect emerges. By introducing a shared halo parameterization, they made the previously disjoint data mutually constrained, thereby changing their evidential role. I develop this idea through two concepts - evidential reconfiguration and structural novelty - leveraged through Myrvold's Bayesian account of unification. The result makes Bayesianism faithful to the inferential practices in this significant part of scientific history, explains how the 1974 papers strengthened the evidential case for dark matter, and expands the Bayesian toolbox with a way to treat novel structure as epistemologically salient.