system
Given the following post, respond as if you're commenting on Reddit:
human
What was the most commonly held scientific theory regarding the origin of the universe and what observation led scientists to question this theory compared to the big bang ? 

Can't find anything on the internet, all i can find is either "what is the big bang theory" or the bloody popular tv series.
gpt
Many people used to believe in a static universe, which had no beginning. Einstein actually adjusted the basic equation of general relativity by adding a constant in order to allow for such a universe to exist. It was only when Hubble collected data on the velocities of distant galaxies relative to us, and found that they were, in general, moving away from us with a velocity proportional to their distance, that people realized that, rather than being static, the universe was expanding. At that point, it was just a matter of running the math backward to realize that the universe must have been infinitesimally small at some point.