The discussion centers on the origins of the idea that the universe is expanding, attributing the initial theoretical framework to Alexander Friedmann, who developed the expanding solutions of General Relativity in the early 1920s. However, it was Edwin Hubble's observational evidence in 1929 that provided the first concrete proof of this expansion, demonstrating a correlation between redshift and distance. Despite Friedmann's earlier work, he was not fully convinced of its physical implications, while Hubble's findings shifted the scientific consensus. The conversation also touches on Einstein's initial rejection of an expanding universe, which he later accepted following Hubble's measurements. Overall, Hubble is recognized for his pivotal role in establishing the expanding universe concept through empirical evidence.