Stephen Hawking's original singularity theorems from the 1960s and '70s were written up on the whiteboards on set.
Jim Parsons revealed that the writers originally wanted him to enter the university restaurant while wearing a metal bikini like Princess Leia in Star Wars: Episode VI - Return of the Jedi (1983). He said that he would only do it if they gave him six months and a personal trainer, so they conceived of the French maid costume instead.
According to Chuck Lorre's Vanity Card at the end of The Gates Excitation (2018), which commemorated the passing of Stephen Hawking, Lorre himself directed the scene between Hawking and Jim Parsons (Sheldon). Lorre mentioned that this was a meeting he couldn't possibly prepare for, so it was full of "nervous, dim-witted pleasantries". His biggest blunder, though, was starting the scene by looking at the immovable Hawking and yelling "Action!" Fortunately, no one else noticed. Lorre praised Hawking for his "fierce sense of humor" and "willingness to laugh despite the enormous difficulties he faced", and the many times that he ultimately appeared on the show.
Although Sheldon "begged TNT to cancel Babylon 5 (1993)", by the time the show was airing on TNT, it only had one year left in its scheduled run.