Marie Gueguen

Measuring the rate at which the universe expands at a given time–the ‘Hubble constant’– has been a topic of controversy since the first measure of its expansion by Edwin Hubble in the 1920s. As early as the 1970s, Sandage and de Vaucouleurs have been arguing about the adequate methodology for such a measurement. Should astronomers focus only on their best indicators, e.g., the Cepheids, and improve the precision of this measurement based on a unique object to the best possible? Or should they “spread the risks”, i.e., multiply the indicators and methodologies before averaging over their results? Is a robust agreement across several uncertain measures, as is currently argued to defend the existence of a ‘Hubble crisis’ more telling than a single 1% precision measurement? This controversy, I argue, stems from a misconception of what managing the uncertainties associated with such experimental measurements require. Astrophysical measurements, such as the measure of the Hubble constant, require a methodology that permits both to reduce the known uncertainties and to track the unknown unknowns. Based on the lessons drawn from the so-called Hubble crisis, I sketch a methodological guide for identifying, quantifying and reducing uncertainties in astrophysical measurements, hoping that such a guide can not only help to re-frame the current Hubble tension, but serve as a starting point for future fruitful discussions between astrophysicists, astronomers and philosophers.

Duhem’s philosophy of science is difficult to classify according to more contemporary categories like instrumentalism and realism. On the one hand, he presents an account of scientific methodology which renders theories as mere instruments. On the other hand, he acknowledges that theories with particular theoretical virtues offer a classification of experimental laws that “corresponds to real affinities among the things themselves.” In this paper, we argue that Duhem’s philosophy of science was motivated by an anti-sceptical tendency, according to which we can confidently assert that our theories reveal truths about nature while, at the same time, admitting that anti-scepticism should be moderated by epistemic humility. Understanding Duhem’s epistemological position, which was unique amongst French philosophers of science in the beginning of the 20th century, requires a careful examination of his accounts of representation, explanation, and of their interrelation.

Although logical empiricism is now mostly decried, their naturalist claim that the content of a theory can be read off from its structure, without any philosophical considerations needed, still supports traditional strategies to escape cases of underdetermination. The appeal to theoretical equivalence or to theoretical virtues, for instance, both assume that there is a neutral standpoint from which the structure of the theories can be analyzed, the physically relevant from the superfluous separated, and a comparison made between their theoretical content and virtues. In my dissertation, I examine the presuppositions upon which such strategies depend. I argue that the methodological principle underlying them, according to which theories with no superfluous structure should be preferred, is unpractical, for what constitutes relevant structure is determined by epistemic considerations about the aim of scientific theories. In chapter 1, I analyze the claim that theories with ordinary bosons and fermions are theoretically equivalent to theories with exotic `paraparticles'. I argue that this claim does not do justice to the latter, as the proof is formulated in a vocabulary parochial to the former and thus favors one of the theory while giving an impoverished version of the second. In chapter 2, I examine recent arguments to the effects that any interpretation of Quantum Mechanics that can offer a no-go theorem against paraparticles possesses an explanatory advantage over other interpretations and should, as such, be favored over others. Given that most physicists consider paraparticles as surplus structure whose non-observation does not require an explanation, I evaluate arguments of both sides and suggest a third way to approach the question. Finally, in chapter 3, I turn my attention to methods for excluding another kind of unphysical structure, mathematical artifacts, from rival dark matter models. Simulations are our only window into what rival models predict about the universe’s structure. But for them to play a useful role in generating knowledge, we need to distinguish reliably between real predictions and artifacts. I argue that robustness analysis fails to fulfill this task. I propose in its place another methodology, that of crucial simulations.