Summary: Mensa-fied best friends and roommates Leonard and Sheldon, physicists who work at the California Institute of Technology, may be able to tell everybody more than they want to know about quantum physics, but getting through most basic social situations, especially ones involving women, totally baffles them. How lucky, then, that babe-alicious waitress/aspiring actress Penny moves in next door. Frequently seen hanging out with Leonard and Sheldon are friends and fellow Caltech scientists Wolowitz and Koothrappali. Will worlds collide? Does Einstein theorize in the woods?
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S03, E12 (First Aired:
Sheldon and Koothrappali attend a university mixer; Leonard discovers that Penny believes in psychics.
S03, E13 (First Aired:
After their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.
S03, E14 (First Aired:
Sheldon tries to figure out the answer to a physics problem by working with Penny.
S03, E15 (First Aired:
Leonard must choose who to bring with him when he goes to see the Large Hadron Collider on Valentine's Day.
S04, E02 (First Aired:
Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.
S04, E03 (First Aired:
When Sheldon searches for an alternative to human companionship, the guys become concerned.
S04, E04 (First Aired:
An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.
S04, E05 (First Aired:
Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.
Penny learns there are fans of her performance in ``Serial Ape-ist'' when she and Leonard attend a Comic Con event; Amy hosts a brunch at Penny's apartment; Wolowitz makes an impulsive purchase.
S04, E08 (First Aired:
While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.
S04, E09 (First Aired:
Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.
S04, E10 (First Aired:
Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.
S04, E12 (First Aired:
Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.
S04, E13 (First Aired:
Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.
S04, E14 (First Aired:
Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.
S04, E16 (First Aired:
Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.
S04, E17 (First Aired:
Sheldon is upset when he realizes Leonard is the center of their group of friends.
S04, E18 (First Aired:
Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.
S04, E20 (First Aired:
Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.
S04, E22 (First Aired:
Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.
S04, E23 (First Aired:
Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.
S04, E24 (First Aired:
Bernadette gets her Ph.D., inspiring the guys to tease Wolowitz about his lack of a doctorate; Raj becomes Sheldon's roommate.
S05, E01 (First Aired:
Penny worries that she has ruined her relationship with her friends; Sheldon takes over the paintball team.
S05, E02 (First Aired:
Amy is caught in the middle when Penny and Sheldon get into an argument over a pre-owned chair; Leonard tries to make his long-distance relationship more exciting.
S05, E03 (First Aired:
Amy and Leonard try to become better acquainted; Bernadette, Howard and Mrs. Wolowitz spend the weekend together.
S05, E04 (First Aired:
Raj wants a girlfriend, so Penny introduces him to a woman he can communicate with.
S05, E05 (First Aired:
Wil Wheaton invites Leonard and Sheldon to a party at his house; Howard receives an opportunity.
S05, E06 (First Aired:
Sheldon finds himself competing with the gang for his mother's (Laurie Metcalf) attention when she visits.
S05, E07 (First Aired:
An attractive comic book artist tests Leonard and Priya's relationship; Sheldon tries to scare his friends.
S05, E08 (First Aired:
Amy is devastated when Penny and Bernadette shop for wedding dresses without her.
S05, E10 (First Aired:
Sheldon is jealous when Stuart (Kevin Sussman), a guy from the comic book store, asks Amy out on a date.
S05, E11 (First Aired:
Leonard must face the bully who targeted him in high school; Penny confronts her past actions.
S05, E12 (First Aired:
Amy is upset with Sheldon when he isn't impressed with her recent accomplishment; Howard struggles with Bernadette's aversion to children.
S05, E13 (First Aired:
Everything could change when Leonard spontaneously invites Penny to a romantic dinner.