20/11/2020 – Marie Gueguen: Replicability in cosmology: lessons to be drawn from the Hubble constant so called ‘crisis’


Since the Santa Barbara conference in July 2019,  where the most recent measurements of the Hubble constant were announced, there is a sense of crisis  with respect to the standard model of cosmology. Indeed, the tension that had already been observed between the low value of the early universe-based measurement of the Hubble constant and the high value found for late universe-based measurements of the same constant has only been worsened by the development of new techniques for measuring H0, which seem to agree with the high value and challenge the standard model. On one side of the debate, the robustness of the high value is taken to confirm that systematic errors possibly explaining the discrepancy have been excluded and that something is wrong with the standard model of cosmology. Hundreds of papers have already been published, suggesting solutions to the Hubble crisis by amending or replacing the standard model. On the other hand, some astrophysicists insist that the chequered history of the Hubble constant measurements shows that extra prudence is needed in estimating the amount of random and systematic errors and their potential impact on the H0 value. How should we then evaluate and react to this discrepancy? Does this tension really call for a crisis in astrophysics and cosmology? And how can we explain why different teams react differently to this tension, some calling it a crisis, the others a ‘surd’? 
In this talk, I will argue that the diverging reactions of different teams find their roots in a lack of conceptual tools to frame the debate. The concept of robustness, in this context, is both vague and non-informative, and does not allow for defining a precise criterion for when the standard model of cosmology would really be in trouble.  Thus, I suggest other tools, inherited from the replicability crisis as discussed in other scientific areas, to reframe the debate,  and to help defining such a crisis criterion.

Biographical information:

Marie Gueguen completed her PhD at the University of Western Ontario in 2019. Her research focuses on the following question: how can the clarification of the structure of scientific theories help us choosing among competing theories, when their observational consequences either are the same or cannot be easily determined. She develops this research program along two main axes: 1) a formal axis, which focuses on showing how artifacts are generated within scientific theories and how their removal can break the alleged equivalence of rival theories; 2) a practice-based approach, in which she studies and formalizes the methods developed by cosmologists to detect artifacts in numerical simulations and assess whether these methods can be suitably applied to scientific theories in general. Upon leaving the Center, Marie took a post as Research Associate at the Rotman Institute of Philosophy. She will follow that with a Marie Curie fellowship hosted in the Institute of Physics of Rennes 1.


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