Virginia Trimble (UCI)

Discovering the Dark: 1921-1986

Abstract:

That one could discover invisible things from their gravitational effects on visible ones was understood in the 19th century by Bessel, LeVerrier, and others. The first deliberate searches for dark matter (already given that name in English) on the scale of our Galaxy began in 1922 with Kapteyn and Jeans. The first positive results (in our whiggish sense) came from Fritz Zwicky (Coma cluster 1933) and Sinclair Smith (Virgo cluster 1937). By the outbreak of WW II, one could have plotted existing data to show that the mass to light ratios of astronomical entities increased monotonically with the length scales on which they were measured ... if anyone had thought to do it. In practice, dark matter was gradually rediscovered over the next 30 years, among much doubt and dispute, and the first such plots appeared in print in 1974. Another dozen years sufficed to rule out traditional candidates like diffuse gas or faint galaxies and to identify most of the entitites that are still part of the possible inventory.