In 1929 Edwin Hubble discovered that the Universe is expanding, which led to the Big Bang theory.

UNESCO: 2008 UK and Ireland Fellows

He would visit Edwin Hubble at Mount Wilson shortly after his meeting with Slipher.

FORBES: Flagstaff's Role In The Expanding Universe

When Edwin Hubble discovered in the 1920s that there were multiple galaxies and that the universe must be expanding, such distances became even less fathomable.

FORBES: The Universe and Mrs. Ferguson

Edwin Hubble never really embraced the notion of the expanding universe.

FORBES: Science and Censorship