Jamee Elder

In April 2019, the Event Horizon Telescope Collaboration released the first image of the shadow of a black hole. Starting off with its early history, and then moving on to these recent developments, we trace the concept of directness in black hole imaging. Throughout this history, “direct observation,” “direct image,” “direct evidence,” and “direct visual evidence” were almost never defined and yet such notions came to be used to argue that imaging would be the most convincing evidence for the existence of black holes. Within the Event Horizon Telescope Collaboration, views about what directness entailed differed and revealed subtle differences between various stances on evidence and visuality. Following the study of directness in black hole imaging, we compare these uses of directness with cases from black hole research more broadly. From a philosophical perspective, “directness” is used to compare one observation to another, across dimensions of varying epistemological significance. This can have implications for the perceived prestige of the observations. However, any connection between directness and epistemological value is highly dependent on the details of both the observation itself and the notion of directness being deployed to describe it.

We evaluate the roles general relativistic assumptions play in simulations used in recent observations of black holes including with LIGO-Virgo and the Event Horizon Telescope. In both experiments, simulations play an ampliative role, enabling the extraction of more information from the data than would be possible otherwise. This comes at a cost of theory-ladenness. We discuss the issue of inferential circularity, which arises in some applications; classify some of the epistemic strategies used to reduce the extent of theory-ladenness; and discuss ways in which these strategies are model independent.

The LIGO-Virgo Collaboration achieved the first ‘direct detection’ of gravitational waves in 2015, opening a new “window” for observing the universe. Since this first detection (‘GW150914’), dozens of detections have followed, mostly produced by binary black hole mergers. However, the theory-ladenness of the LIGO-Virgo methods for observing these events leads to a potentially-vicious circularity, where general relativistic assumptions may serve to mask phenomena that are inconsistent with general relativity (GR). Under such circumstances, the fact that GR can ‘save the phenomena’ may be an artifact of theory-laden methodology.This paper examines several ways that the LIGO-Virgo observations are used in theory and hypothesis testing, despite this circularity problem. First, despite the threat of vicious circularity, these experiments succeed in testing GR. Indeed, early tests of GR using GW150914 are best understood as a response to the threat of theory-ladenness and circularity. Each test searches for evidence that LIGO-Virgo’s theory-laden methods are biasing their overall conclusions. The failure to find evidence of this places constraints on deviations from the predictions of GR. Second, these observations provide a basis for studying astrophysical and cosmological processes, especially through analyses of populations of events. As gravitational-wave astrophysics transitions into mature science, constraints from early tests of GR provide a scaffolding for these population-based studies. I further characterize this transition in terms of its increasing connectedness to other parts of astrophysics and the prominence of reasoning about selection effects and other systematics in drawing inferences from observations.Overall, this paper analyses the ways that theory and hypothesis testing operate in gravitational-wave astrophysics as it gains maturity. In particular, I show how these tests build on one another in order to mitigate a circularity problem at the heart of the observations.