My research focuses on the epistemic status of empirical evidence in cosmology. Due to the complexity of the evolution of the universe, and the exponential growth of cosmological and astrophysical observations throughout the 20th century, cosmology raises new questions about empirical evidence for philosophers of science. What epistemic justification underpins the generation of empirical data in a scientific field with a remote and exotic target? And how can that data be amalgamated or serve in theory testing? My work draws on and contributes to insights from general philosophy of science as well as to the nascent field of philosophy of cosmology.

Evidence Generation: Cosmology as an Integrative Science​
I develop an account of cosmology as an integrative science by investigating the epistemic underpinnings of how empirical methods and lines of evidence can come to bear on cosmological model-building. The common challenges associated with integration are exacerbated in cosmology by the unknown nature of dark matter and dark energy, together 95% of the energy density of the universe. I highlight three challenges to successful integration in cosmology, and how cosmologists can respond to them.

1. How can existing experimental techniques responsibly be applied to genuinely novel physics? I argue that this sometimes requires substantive assumptions about the novel target. This 'method-driven logic' is different from how experiments are usually justified. 
2. Whether or not a line of evidence results from a method-driven experiment affects the warrant that this evidence can provide for conclusions about the target. I highlight an apparent paradox of success: while negative results allow for secure constraints on the theory of the target, the warrant from positive results is less clear. 
3. With accelerator experiments reaching their limits, particle physics has started to exploit the early universe as a new source of evidence. This is a substantive methodological shift. I am interested in what epistemic shift is associated with this methodological shift, if any. 

Evidence Evaluation: Anomalies in Cosmology
A second research area is centered on anomalies in cosmology. Anomalies present a recurring challenge for philosophers of science: when does an apparent discrepancy between a theoretical prediction and an empirical observation or between different empirical observations constitute a genuine anomaly (and thus a problem for the theory), and are there contexts where it can temporarily be ignored for the pursuit of other goals? Although many attempts have been made in the past, it seems impossible to formulate universally applicable necessary and sufficient conditions to distinguish the two situations above. Instead, I draw on the history of cosmological practice to make headway on the question of anomalies. 

1. I am developing a bottom-up view on disagreements between predictions and observations in cosmology. One issue is that predictions in cosmology are often derived from computer simulations, which affects the evaluation of the discrepancy as a genuine anomaly and the appropriate response. Another issue is the status of correlations: should scientific models explain any and all correlations with instrumental value, or does recovery of the underlying data suffice? 
2. Cosmologists are often confronted with disagreements between different lines of evidence. I have various projects on discordant evidence in cosmology, where I evaluate the philosophical underpinnings of the proposed resolutions of the discordance, and how these proposed resolutions bear on the existing literature on evidence amalgamation and triangulation.

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Cartoon by Willem de Sitter in the Algemeen Handelsblad (9 July 1930). The caption in Dutch reads "Who is blowing up the balloon? What makes the universe expand, or swell up? That must be the Lambda, no other answer can be given!" (my translation). Retrieved from the Leiden University Library, Leiden Observatory Archives, directorate Willem de Sitter, call number Leiden UB, AFA FC WdS 248-3-004

A visual representation of ΛCDM, the standard model of cosmology. Image credit: ESA / The Planck Collaboration