Conceptual Expansion
In 1912, American astronomer Vesto Slipher claimed that there were galaxies outside our own, having stars too far away to belong to the Milky Way. This radical notion was opposed by many in the astronomy establishment; a universe with more than 1 galaxy was ridiculous. In time, Slipher’s conviction prevailed, as further work convinced astronomers and physicists that the universe was expanding, having grown far astray of being just the Milky Way.
American astronomer Edwin Hubble is often wrongly credited with the discovery of distant galaxies. Hubble was at Slipher’s 1912 lecture and carried the conviction publicly.
Hubble’s law, which characterizes the Doppler shift of receding galaxies, was based upon Slipher’s data. The law was first derived by Georges Lemaître. Hubble confirmed the law, determined a more accurate measurement, and took credit.
Armed with an estimated size of the present universe, and a bogus guess about how long ago the cosmos debuted, cosmologists struggled to explain how the universe got from its supposed moment of inception to where it is today. There was an unfathomed gap between how small the universe supposedly started off as and how big it seems to be now; so the yawning gulf was filled with expansive stuffing.
