Raj meets with the woman his father set up for him, Anu. Her commanding personality and practical approach to marriage startle Raj but he agrees to go ahead with it. Howard criticizes him but apologizes; he just never expected Raj to give up on romance. Raj admits this to Anu so she proposes to him, and he says yes. Raj also sends out a relationship questionnaire to Leonard and Penny, which soon reveals that Penny does not think she ever wants kids, upsetting Leonard, who would like to have kids someday, and their friends selfishly badger them on the issue. After telling her father Wyatt who is also upset, Leonard tells Penny that he'll be okay with it, as he never thought he'd have her in his life. To get his mind off of it, Penny rents Leonard a Batmobile to drive in and have fun with for the day. Meanwhile, Stuart starts bringing home Denise at night, which is very uncomfortable for Howard and Bernadette. When they also try to have time to themselves, they wake up their kids.
The show originally centered on five characters living in Pasadena, California: Leonard Hofstadter and Sheldon Cooper, both physicists at Caltech, who share an apartment; Penny, a waitress and aspiring actress who lives across the hall; and Leonard and Sheldon's similarly geeky and socially awkward friends and co-workers, aerospace engineer Howard Wolowitz and astrophysicist Raj Koothrappali. Over time, supporting characters were promoted to starring roles, including neuroscientist Amy Farrah Fowler, microbiologist Bernadette Rostenkowski, physicist Leslie Winkle and comic book store owner Stuart Bloom.
Leonard gives an interview on public radio where he admits physics research might be at a dead end. The university is furious and, while trying to think of reasons to put in a retraction, he depresses Sheldon into thinking he might be right. Howard and Raj come over and end up just as depressed. Getting drunk with Penny, the men go to the grave of Richard Feynman and realize there is hope for physics as long as they believe in it. Leonard accidentally sends a drunken email to Human Resources. Meanwhile, Amy and Bernadette agree with each other to keep quiet about the success in their careers so as not to upset Sheldon and Howard. While bragging to each other, they end up arguing which of their fields is better.
The Big Bang Theory signs off for good on Thursday, May 16, meaning that there's only one last bazinga left in the pipeline before we're forced to say farewell to Sheldon, Leonard, Penny, and the gang after 12 laugh-filled seasons. And while there's still a few questions left to be answered by the big one-hour series finale—Will the elevator ever be fixed? And will we ever learn Penny's maiden name?—there's a bigger one looming for when the credits roll and it's all over.
Showrunner Steve Molaro, who took over from Bill Prady with the sixth season, credits some of the show's success to the sitcom's exposure in off-network syndication, particularly on TBS, while Michael Schneider of TV Guide attributes it to the timeslot move two seasons earlier. Chuck Lorre and CBS Entertainment president Nina Tassler also credit the success to the influence of Molaro, in particular the deepening exploration of the firmly established regular characters and their interpersonal relationships, such as the on-again, off-again relationship between Leonard and Penny. Throughout much of the 2012–13 season, The Big Bang Theory placed first in all of syndication ratings, receiving formidable competition from only Judge Judy and Wheel of Fortune (first-run syndication programs). By the end of the 2012–13 television season, The Big Bang Theory had dethroned Judge Judy as the ratings leader in all of syndicated programming with 7.1, Judy descending to second place for that season with a 7.0. The Big Bang Theory did not place first in syndication ratings for the 2013–14 television season, beaten out by Judge Judy.
Leonard and Sheldon are brilliant physicists—geniuses in the laboratory but socially challenged everywhere else. Enter beautiful, street-smart neighbor Penny, who aims to teach them a thing or two about life. Despite their on-again, off-again relationship in the past, Leonard and Penny have finally gotten married. Even Sheldon has found a female companion, entering into a "relationship agreement" with neurobiologist Amy Farrah Fowler, and he recently took their relationship to the next level by marrying her after a long courtship. In their free time, Leonard and Sheldon enjoy fantasy role-playing games with their ever-expanding universe of friends, including fellow scientists Koothrappali, Wolowitz, and Wolowitz’s adorable microbiologist wife, Bernadette, who is adjusting to life with their two children.
When Leonard receives a braggy Christmas letter from his brother, he feels bad about how little he and Penny have achieved in the past year. Leonard wonders if he and Penny should be thinking about the next step after two years of marriage, like buying a house or having a baby. Penny tells him she wants to do all those things someday, but she has a bunch of stuff she would like to do first.