Sheldon's childhood friend from Texas, Tam, is visiting the university with his son. Sheldon does not want to see him and the others wonder why Sheldon has never mentioned Tam. Tam is unaware Sheldon is angry with him, thinking they just naturally drifted apart. Sheldon's brother George does not know the reason either. Sheldon eventually reveals Tam promised he would move to California with Sheldon, but then got a girlfriend and stayed with her, leaving Sheldon feeling abandoned. Tam and Sheldon make up and Sheldon has Leonard take Tam to the airport. Meanwhile, Penny and Bernadette want to get to know Anu, impressed by her connections in the hotel industry. They tell her embarrassing things about Raj and wonder if they can go out with her again after Raj confronts them.
When Penny tells Leonard he needs to be more assertive in making decisions for himself, he starts standing up to Sheldon over small things. His confidence makes him want to demand the university support his idea for a plasma physics project. He threatens to quit if the university refuses, alarming both Sheldon and Penny, who consider this to be a risky career move. Sheldon is conflicted on whether or not he is being selfish over Leonard's decision, but Amy suggests that the fact that he is worried over Leonard's motivation proves that he does care about him, which he acknowledges. President Seibert refuses the project, but in order not to lose Leonard, gives him co-leadership over a photon entanglement project, leaving Leonard proud of himself and Penny impressed. Meanwhile, Raj shows Anu his lab, and suggests one possible answer for something he's seen in space might be alien life. When someone mentions this at his observatory presentation, the scientific community starts mocking him as a conspiracy theorist. Raj points out scientists should consider all possibilities when seeking the truth, though this causes people to think he believes in the Loch Ness Monster.
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.[209] 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".[210]

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.”
After learning Sheldon went behind their backs to work with the military again, Leonard and Howard say Sheldon is like Thomas Edison, taking credit for others' ideas, while they are more like Nikola Tesla. Leonard and Howard bring in Barry Kripke to help create a better idea than Sheldon's, but Kripke goes to the military himself, cutting all three of them out. Meanwhile, Bernadette fears Ruchi is trying to steal her projects at work while she is on maternity leave and enlists Raj to spy on her. Though he finds proof that Ruchi may be stealing from Bernadette, Raj tries to defend Ruchi like a boyfriend would, pointing out Bernadette's hypocrisy as she would most likely have stolen from other people's projects as well. Ruchi is not happy about this and promptly dumps Raj.
Sheldon needs half a billion dollars to prove his latest concept of string theory, which the University cannot afford to fund. Crowdfunding and selling some of his most valuable comic books to Stuart give him a small start. When Raj mentions gambling in Las Vegas, Sheldon goes there but is caught calculating odds by security before he can make any bets. Meanwhile, Amy takes Penny and Bernadette shopping for her wedding dress. She loves an old-fashioned one that the other girls admit that they find ugly, though Penny assures Amy she can make her own decisions about her wedding. Sheldon, however, comes home and sees Amy in the dress and loves how she looks.
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.
Producers, writers and others, including recurring guest star Wil Wheaton, joined the festivities on set and — hardly a spoiler alert — more laughing, crying and hugging ensued. Lorre embraced a happy Parsons, then moved on to each cast member as if it were a reception line. Galecki shared long, emotional hugs with his colleagues. After trying to keep their emotions under control for so long, it was finally time to just let go.

In March 2017, CBS renewed the series for two additional seasons, bringing its total to twelve, and running through the 2018–19 television season.[3] On August 22, 2018, CBS and Warner Bros. Television officially announced that the twelfth season would be the series' last. This stems from Jim Parsons' decision to leave the series at the end of the season if the show were to have been renewed for a thirteenth season.[1][4][5] The series concluded with an hour-long finale consisting of two back-to-back episodes on May 16, 2019.[6][7] A retrospective, hosted by Johnny Galecki and Kaley Cuoco, aired at 9:30 P.M. ET/PT, the night of the finale, following the season two finale of Young Sheldon.[8]


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.[209] 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".[210] 

The Canadian alternative rock band Barenaked Ladies wrote and recorded the show's theme song, which describes the history and formation of the universe and the Earth. Co-lead singer Ed Robertson was asked by Lorre and Prady to write a theme song for the show after the producers attended one of the band's concerts in Los Angeles. By coincidence, Robertson had recently read Simon Singh's book Big Bang,[25][26] and at the concert improvised a freestyle rap about the origins of the universe.[citation needed] Lorre and Prady phoned him shortly thereafter and asked him to write the theme song. Having been asked to write songs for other films and shows, but ending up being rejected because producers favored songs by other artists, Robertson agreed to write the theme only after learning that Lorre and Prady had not asked anyone else.[citation needed]

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.[209] 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".[210]
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