Cosmic Stories: Astrophysics and the Invention of Cosmology in the Early 20th-Century

The papers in this session recall the intellectually-challenging context in astronomy and astrophysics at the turn of the 20th century, when a wealth of empirical data became available, giving rise to a host of new, and quite puzzling statistical correlations, the reality of which was often deemed uncertain. Several theorists braved the uncertainties, drawing on the new correlations to elaborate models of stellar dynamics, and of the nature and structure of the universe. Inspired by kinetic gas theory, in 1901 William Thomson (Lord Kelvin) calculated the dimensions of the universe based on star velocities in the vicinity of the Solar System, giving rise to "stargas" models of the universe, pursued from various angles by J. C. Kapteyn, Henri Poincaré, Arthur Eddington, Karl Schwarzschild, James Jeans, C. V. L. Charlier, and Albert Einstein, from 1906 to 1924. Meanwhile, new theories of the electron and the atom enabled astronomers to investigate the physical properties of stars and explain many of the new correlations. Both Eddington and Anton Pannekoek took a pragmatic, inquisitive approach: Eddington, in his investigations on the internal constitution of stars, valued gaining physical insight over mathematical rigor, while Pannekoek focused on precision measurements and laborious numerical models to determine the physical conditions in the outer layers of stars. Together, these four talks, based largely on previously-unexploited archival sources, provide a richer picture of the ground-breaking developments in early 20th-century astrophysics and cosmology.