Edwin Hubble, an Infinite Universe, and the Classification of Galaxies

Abstract

The Great Debate was inconclusive. It failed to resolve a basic dispute critical to understanding the universe: Were we alone in the Milky Way as the only galaxy in the universe or did others exist? Was, for example, M31, the Andromeda Nebula, something distinct from the Milky Way, perhaps a separate galaxy existing on its own, or was it simply part of ours? To conclude that Andromeda was a unique galaxy also had broader implications, suggesting that perhaps other galaxies, in the millions if not billions or more, existed that were distinct from the Milky Way. Additionally, perhaps many of the other phenomena observed in the sky, too, might be separate from the Milky Way? But how to resolve this debate?