Raj hooks up with a recently separated woman, Nell, after one of his lectures at the planetarium. Her husband, Oliver, confronts Raj at the planetarium and then breaks down over the end of his marriage. After comforting Oliver, Raj talks to Nell and convinces her to give her husband another chance. Meanwhile, after diving once again into string theory and sprawling his work across his and Amy's apartment, Sheldon approaches a reluctant Leonard and Penny and convinces them to let him use his old room to study for a three-day trial period with an agreement to be quiet and stay out of their way. Sheldon surprisingly sticks to this agreement, being a reasonably good guest, which shockingly frustrates Leonard to no end. After Leonard lets out his frustrations, Sheldon then renegotiates the guest tenancy agreement for an extra few days and resumes being his normal demanding self, much to Leonard's relief.
It was really hard to pick the right pic for this post, so here is a shot of us in a hug after we filmed the last group scene we would ever film for the series... and TONIGHT is THE NIGHT... it’s the series finale at 8pm EST and then there’s the Young Sheldon (season!) finale, and then a special behind the scenes show hosted by @kaleycuoco and @sanctionedjohnnygalecki and then the entire cast is on @colbertlateshow I hope you get a chance to tune in and i hope you enjoy all of it. If you enjoy it even half as much as we’ve enjoyed (LOVED) creating this show for the past 12 years, then that’ll be a WHOLE WHOLE lot of enjoyment. All of us will miss seeing you in this format, but we will be around in all sorts of ways, I assure you... love love love ❤️❤️❤️
Although the original pilot was not picked up, its creators were given an opportunity to retool it and produce a second pilot. They brought in the remaining cast and retooled the show to its final format. Katie was replaced by Penny (Kaley Cuoco). The original unaired pilot has never been officially released, but it has circulated on the Internet. On the evolution of the show, Chuck Lorre said, "We did the 'Big Bang Pilot' about two and a half years ago, and it sucked ... but there were two remarkable things that worked perfectly, and that was Johnny and Jim. We rewrote the thing entirely and then we were blessed with Kaley and Simon and Kunal." As to whether the world will ever see the original pilot on a future DVD release, Lorre said, "Wow, that would be something. We will see. Show your failures..."
After Neil Gaiman tweets about Stuart's comic book store, it becomes very popular, and the crowds upset Sheldon. Stuart hires an assistant manager named Denise and she impresses Sheldon with her comic recommendations. Amy goes to her for information on comics to connect to Sheldon but when she tries to tell him, he says he's talked enough about comics with Denise. The store's popularity causes Stuart to be unable to babysit for Howard and Bernadette's date night. They try to have another at home, but Stuart shows up so they hurriedly go out. Meanwhile, as Raj sets up a telescope, Penny sees a new comet. Raj takes sole credit for the discovery, angering Penny. Leonard tries to defend her but feels sorry for hurting Raj's career. Penny confronts Raj herself and he agrees to share credit after Penny doesn't give in like Leonard.
Howard dresses as Sheldon for Halloween at work, hurting Sheldon's feelings. When Howard does not apologize, Amy and Sheldon dress as Bernadette and Howard at Penny and Leonard's party, angering Bernadette. Sheldon and Bernadette later bond over their painful childhood memories. Leonard is upset that Penny does not seem to remember that their first kiss was on Halloween. Penny later admits she does remember, but does not like to think of their first kiss as an unromantic drunken hookup. She likes to imagine their first kiss was one they shared on Leonard's birthday, which pleases him.
Penny and Bernadette attend a pharmaceuticals conference, where Bernadette's business rival Danny tries to recruit Penny. Bernadette is offended that Penny is considering the offer. At the meeting with Danny, Bernadette steps in to say Penny is the best saleswoman she knows and Penny agrees to keep working for Bernadette. Meanwhile, the rest of the gang does simple behavioral experiments on the Wolowitz children using a book Sheldon found. Leonard is shocked that his childhood was filled with these experiments; although his mother remembers that time with him fondly, she admits the experiment with him is not over. Raj figures Amy planted the book to get Sheldon to like babies, though Sheldon later states he would be open to having kids.
Two nerdy physicists share an apartment and an unlikely friendship with their beautiful neighbor with whom one of them is infatuated. Like the universe after the big bang, the show's popularity expanded, thanks to breakout star Jim Parsons, along with the chemistry among the friends and the developing romance between Leonard and Penny. The addition of Melissa Rauch and Mayim Bialik in later seasons also enhanced the stories and relationships of the leads.
Filming proceeds smoothly – makeup artists do touch-ups, a prop master replenishes the pickle supply – with humor and camaraderie between takes. When a reshoot is needed because Simon Helberg, who plays Howard, held his napkin in the wrong hand, Kaley Cuoco, who plays Penny, lifts her food box high and mockingly asks, “Does it go over my head? I don’t remember.”
The episode opens with a short montage of clips from the series' twelve seasons, then segues to Sheldon and Amy, who are up late waiting for a call from the Nobel Committee. Following a prank call from Kripke, they are told they've won the Nobel Prize in Physics for their super-asymmetry work. The attention from the media and the university bothers Sheldon. Amy is saddened by an unflattering picture of her in a news report, so Raj convinces her to get a makeover. She loves her new look but Sheldon demands she change it back. Leonard calls him out for being rude, but Sheldon flees when he sees Penny emerge from the newly repaired elevator. Sheldon and Penny go to the Cheesecake Factory and Penny tells Sheldon that change is the only constant thing in life. On a TV, they see Bernadette and Howard take credit as Sheldon and Amy's best friends. Raj and Leonard defend Amy, with Leonard accidentally breaking Sheldon's DNA molecule model in Apartment 4A. Penny convinces Sheldon to ride in the elevator.
However, no legal action was required to end production of the other show: as soon as it became known that the show was unlicensed, the actors quit and the producers canceled it. Dmitriy Tankovich (who plays Leonard's counterpart, "Seva") said in an interview, "I'm upset. At first, the actors were told all legal issues were resolved. We didn't know it wasn't the case, so when the creators of The Big Bang Theory started talking about the show, I was embarrassed. I can't understand why our people first do, and then think. I consider this to be the rock bottom of my career. And I don't want to take part in a stolen show".