Who first argued that galaxies were 'island universes' in the Great Debate of 1920? A. Heber Curtis B. Edwin Hubble C. Harlow Shapley
I can find reference to both Curtis and Shapley. Thanks for any help with this one.
//Curtis on the other side contended that Andromeda and other such "nebulae" were separate galaxies, or "island universes" (a term invented by the 18th-century philosopher Immanuel Kant, //