"Edwin Hubble as a young man. It was then that he said, “If only I could find some principle for whose sake I could leave everything else and devote my life.” He found it, in astronomy. Hubble’s work in astronomy in the 20th century became the foundation for Big Bang theory. Image is a screenshot from a Hubble Space Telescope video."
You might enjoy reading this great article about Edwin Hubble from Earthsky.com, written by Debra Byrd
Edwin Hubble and the expanding universe