Making Modern Earth - Measurement and Theoretical Modelling in Physical Geodesy

My PhD project explores the epistemology of measurement in physical geoscience through an in-depth study of its foundational measurement problem. I present a novel historical analysis of how scientists successfully measured the earth's figure and gravity field, highlighting the problem's central role in the histories of physics, statistics, metrology, and modern earth science, as well as its unique importance for our epistemological understanding of measurement and theoretical modeling.

Different geodetic measurement operations sketched in: Pierre Bouguer and Charles-Marie de La Condamine in La figure de la terre, Paris 1749.

Research Summary

Understanding the inferential structure and justification of scientific measurements is a crucial problem for scientists and philosophers of science alike. However, the classical views that have informed philosophical theories of measurement and various attempts to establish new quantitative measures are almost exclusively based on case studies from experimental physics or behavioural science. My work aims to enrich our understanding of the aims and justification of measurement by focussing on central problems in the modern history of physical geoscience, where measured systems are highly complex and partially inaccessible, while it is virtually impossible to shield measurements from confounding perturbations. In particular, I study how physical geodesists successfully measured the most basic theoretical parameters of the earth, describing its shape, interior density distribution, and gravity field. While earth models involving these parameters are taken for granted in virtually all geoscientific research, accurately measuring them was one of the most challenging tasks in the modern history of science. I provide novel historical analyses of central developments in physical geodesy, including the construction of the first mathematical models and measurements of planetary figures (1680-1730), the emergence of theoretical and statistical methods of data correction (1755-1820), responses to persistent discordances (1820-1870), and the first agreement on a unified model of the earth's figure and gravity field (1880-1930). Throughout these historical studies, I analyse (i) why geodetic measurement was so difficult, (ii) how geodesists conceptualised the aims of their measurements, and (iii) by which means they solved their measurement problems. My responses to these questions challenge the canonical views on (i) the epistemic structure of measurement problems, (ii) how the success of measurements should be evaluated, and (iii) what methodological strategies scientists can use to solve measurement problems.

Hydrostatic derivation of planetary equilibrium figure in: Alexis Clairaut, Théorie de la figure de la terre : tirée des principes de l'hydrostatique, Paris 1743.

Published research from this project:

  • Newton as Geodesist: The Problem of the Earth's Figure and the Argument for Universal Gravitation.* Newsletter of the American Physical Society.

*Winner of the 2022 APS History and Philosophy of Physics Essay Price

*Winner of the 2021 Du Châtelet Price in Philosophy of Physics