Nothing is ever "proven" in non-theoretical physics including cosmology, if your definition of proven is "cannot be falsified". I can trivially replace any cosm

Nothing is ever "proven" in non-theoretical physics including cosmology, if your definition of proven is "cannot be falsified". I can trivially replace any cosmology statement with "well, it all just popped into existence five minutes ago, our respective memories included". But with the discovery of background radiation, contending models were falsified. Most notably the "steady state model", which was considered somewhat more elegant and beautiful. Had I been alive and into physic back then, I totally would have backed steady state over the big bang. Alas, the data speaks louder than what I consider "beautiful".