Leonard and Sheldon publish a paper which is widely accepted except for comments from an internet troll. Meanwhile, the girls reminisce about embarrassing incidents from their past.

Leonard buys a dining room table and it causes Sheldon to reevaluate the changes in his life. Meanwhile, Wolowitz is offered a chance to go back to space and Bernadette…

Sheldon and Raj test whether they could survive a dark-matter research expedition in a salt mine by simulating the conditions in a steam tunnel deep underground. Meanwhile, Leonard and Penny…

After arguing with Sheldon, Howard tries to make amends by taking him to NASA headquarters in Houston. Penny has second thoughts about quitting her waitressing job when her car dies….

Leonard and Amy make an unexpected trip to Arizona to fetch Sheldon; Penny interviews for a job at Bernadette’s company; Stuart’s relationship with Mrs. Wolowitz disturbs Howard.

Sheldon is forced to teach a class as a Junior Professor and Howard decides to enroll in it. Meanwhile, Amy plays both sides when tension arises between Penny and Bernadette.

Sheldon tries to relax after he is forced to take a vacation. Meanwhile, Leonard struggles to be supportive of Penny after she quits her job, and Bernadette seeks Stuart’s help…

Wolowitz feels nervous when he is asked to throw the first pitch at a Los Angeles Angels game. Penny and Leonard want to prove Sheldon wrong after he says he…

Sheldon must choose between joining Amy at her aunt’s birthday party or playing videogames all weekend with the guys.

When Wolowitz gets to work with Stephen Hawking, Sheldon is willing to do anything to meet his hero.

When NASA moves up Howard’s mission, he must face his fears and Bernadette’s dad, thus putting the wedding plans in jeopardy. Meanwhile, Leonard says something surprising to Penny in the…

Sheldon’s selfish demands force Leonard to reconsider their friendship. Meanwhile, Wolowitz tries to pick his astronaut nickname.

Sheldon battles Kripke for a coveted office at the university. Penny receives a very unusual gift from Amy.

Penny is worried with how damaged her friendship with the guys will be in the aftermath of her sleeping with Raj while Sheldon becomes the leader of the paintball team.

Leonard and Amy get to know each other better, while Howard and Bernadette spend the weekend with Mrs. Wolowitz.

Sheldon and Leonard get invited to a party at Wil Wheaton’s house, and Howard gets an out-of-this-world opportunity.

Sheldon’s mother, Mary Cooper, comes to visit, but Sheldon is annoyed that she also spends time with the rest of the gang, instead of catering to his every demand.

Leonard and Penny try hanging out as friends on a ‘non-date’, but end up purposely ruining each others chances with perspective dates. Meanwhile, Sheldon enlists the help of Bernadette and…

Leonard must face his fears after being contacted by his high school tormentor.

Leonard, who broke up with Priya, asks Penny out to a spur-of the-moment romantic dinner for two, and the duo contemplates on their relationship.

Sheldon becomes concerned when everybody begins to hang out at Raj’s apartment and discovers Leonard is the center of the group.

Sheldon and Amy decide to start several rumors about the others as a test. Meanwhile, Howard takes his relationship with Bernadette to even higher level.

When Howard finally breaks the news to his mom that he’s engaged to Bernadette, it lands her in the hospital.

While the guys camp in line for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

Penny’s home business turns into a complete nightmare when Sheldon takes over.

The guys find a “super” use for Penny’s new boyfriend, Zack, when they enter a costume contest as the Justice League.

Hoping it will make him a better teacher, Sheldon has Penny give him acting lessons. Raj has fantasies about a friend’s girlfriend.

Leonard and Koothrappali escort a heartbroken Wolowitz to Las Vegas, and Sheldon becomes locked out of his apartment and must stay with Penny.

Leonard realizes he’s the only one without a girlfriend, while Sheldon wants to get rid of his.

Sheldon and the gang are confused when a young grad student is attracted to him.

Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon’s stringent standards.

Penny’s criticism of Wolowitz’s romantic life pushes him into depression and AWOL for a fighting robot battle the rest of guys are depending on him for.

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.

Leonard and Penny are drawn together after a disastrous visit from Leonard’s mother.

Penny’s first date with Leonard goes awry; Penny finds Sheldon to be an unwilling confidant.

A jealous Leonard reacts to Penny’s new guy by rebounding with Leslie.

Sheldon creates a monster when he introduces Penny to online gaming.

When their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.

Sheldon winds up in traffic court when he gets a ticket because of Penny.

A fight between Leonard and Penny threatens their relationship, while Sheldon battles Wil Wheaton in bowling.