This season the Big Bang gang’s romantic universe expands. On the rebound from Penny, Leonard falls into the arms of Raj’s sister Priya. Sheldon gets a girlfriend, or rather a friend who is a girl: Amy, a dour neurobiologist who declares herself besties with Penny. Howard and Bernadette heat up. And so do Raj and Bernadette (at least in Raj’s Bollywood daydream).
All episodes — Season 4
S4 E1The Robotic Manipulation
Sep 23, 2010821 min
Penny tags along on Sheldon's first ever date; Wolowitz finds a new use for a robotic arm.
S4 E2The Cruciferous Vegetable Amplification
Sep 30, 20107.821 min
Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.
S4 E3The Zazzy Substitution
Oct 7, 20107.521 min
The guys are concerned as Sheldon searches for an alternative to human companionship.
S4 E4The Hot Troll Deviation
Oct 14, 20107.720 min
An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work.
S4 E5The Desperation Emanation
Oct 21, 20107.421 min
Leonard realizes he’s the only one without a girlfriend, while Sheldon wants to get rid of his.
S4 E6The Irish Pub Formulation
Oct 28, 20107.522 min
Leonard keeps an affair a secret from Sheldon, Howard and Raj.
S4 E7The Apology Insufficiency
Nov 4, 20107.621 min
Sheldon's answers during an FBI interview put Wolowitz's security clearance in jeopardy.
S4 E8The 21-Second Excitation
Nov 11, 20107.819 min
While the guys camp in line for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.
S4 E9The Boyfriend Complexity
Nov 18, 20107.921 min
Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a telescope.
S4 E10The Alien Parasite Hypothesis
Dec 9, 20107.420 min
Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who would be the better superhero.
S4 E11The Justice League Recombination
Dec 16, 20107.920 min
The guys find a "super" use for Penny's new boyfriend, Zack, when they enter a costume contest as the Justice League.
S4 E12The Bus Pants Utilization
Jan 6, 20117.421 min
Leonard's idea for a smartphone app derails his friendship with Sheldon.
S4 E13The Love Car Displacement
Jan 20, 20117.721 min
Bernadette runs into her ex-boyfriend while attending a science event with Wolowitz.
S4 E14The Thespian Catalyst
Feb 3, 20117.521 min
Hoping it will make him a better teacher, Sheldon has Penny give him acting lessons. Raj has fantasies about a friend's girlfriend.
S4 E15The Benefactor Factor
Feb 10, 20117.420 min
A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science.
S4 E16The Cohabitation Formulation
Feb 17, 20117.520 min
As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his relationship with Raj's sister.
S4 E17The Toast Derivation
Feb 24, 20117.721 min
Sheldon becomes concerned when everybody begins to hang out at Raj's apartment and discovers Leonard is the center of the group.
S4 E18The Prestidigitation Approximation
Mar 10, 20117.621 min
Sheldon is baffled by Wolowitz's magic trick. Meanwhile, Leonard realizes dating Priya may make it impossible to continue being friends with Penny.
S4 E19The Zarnecki Incursion
Mar 31, 20117.621 min
Sheldon's online-game account is hacked by Todd Zarnecki, who then proceeds to steal all his items prompting the guys to go on a quest to retrieve them. Penny, Bernadette and Amy discuss how Penny groomed Leonard to be willing to try vario
S4 E20The Herb Garden Germination
Apr 7, 20117.921 min
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.
S4 E21The Agreement Dissection
Apr 28, 20117.321 min
When Leonard spends too much time in the shower with Priya, Sheldon charges Leonard with two violations of the roommate agreement. However, before he can get too far, Priya uses her skills as a lawyer to nullify the charges due to the agree
S4 E22The Wildebeest Implementation
May 5, 20117.121 min
Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.
S4 E23The Engagement Reaction
May 12, 20117.620 min
When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.
S4 E24The Roommate Transmogrification
May 19, 20117.621 min
When Bernadette receives her PhD, Wolowitz feels emasculated. Raj and Leonard swap places and Penny does something she's regrets.