- Main article: List of The Big Bang Theory episodes (season 4)
Season 4 of The Big Bang Theory returned to television on September 23rd, 2010 and contained 24 episodes.
- In order of credit
- In order of character appearances
- Aarti Mann as Priya Koothrappali (10/24)
- Carol Ann Susi as Mrs. Wolowitz (7/24)
- Brian Smith as Zack (3/24)
- Kevin Sussman as Stuart (3/24)
- Alice Amter as Mrs. Koothrappali (2/24)
- Brian George as V. M. Koothrappali (2/24)
- John Ross Bowie as Barry Kripke (1/24)
- Wil Wheaton as Himself (1/24)
- Laurie Metcalf as Mary Cooper (1/24)
- Vernee Watson-Johnson as Althea (1/24)
- Joshua Malina as President Siebert (1/24)
|Episode #||Title||Original Air Date||Directed By||Description|
|401||The Robotic Manipulation||September 23, 2010||
Howard demonstrates a robotic arm, that he "borrowed" from the Jet Propulsion Laboratory. To everyone's surprise, Sheldon announces his plans to conceive a progeny with Amy via in vitro fertilization. Penny comes to know of Sheldon's new friend and asks him to take Amy on a date which she ends up chaperoning.
|402||The Cruciferous Vegetable Amplification||September 30, 2010||
Sheldon determines that his best estimate for his life expectancy by changing his diet and then building a robot to take his place.
|403||The Zazzy Substitution||October 7, 2010|
|404||The Hot Troll Deviation||October 14, 2010||
When the guys run into Howard's ex at the Cheesecake Factory, he ends up confronting his lingering feelings for her. He seeks help from Penny, who agrees on the condition that Howard reveal the reason behind his breakup.
|405||The Desperation Emanation||October 21, 2010|
|406||The Irish Pub Formulation||October 28, 2010||
Raj's sister, Priya (Aarti Mann), visits and inadvertently causes trouble for the friends. She and Leonard apparently have a history, despite Leonard's pinky swear with Howard that they would not interact with her in deference to Raj. They hook up, but are discovered by Sheldon, who devises an elaborate lie to cover it up.
|407||The Apology Insufficiency||November 4, 2010||
When Howard attempts to recieve a high security clearance, his friends are interviewed by a formidable FBI agent checking into Howard's past. Raj and Leonard are pathetic during their respective interviews, while reveals too much.
|408||The 21-Second Excitation||November 11, 2010||
Sheldon, Leonard, Raj, and Howard excitedly plan to attend a screening of Raiders of the Lost Ark that includes 21 seconds of never-before-seen footage. However, they delay reaching the theater, resulting in much complaining from Sheldon, which becomes worse when Wil Wheaton arrives. Amy starts to bond with Penny during a sleep over.
|409||The Boyfriend Complexity||November 18, 2010||
Leonard is flattered when he shows up at Penny's door and gets a kiss from Penny. Later, Penny informs him that her critical father Wyatt (Keith Carradine) is visiting, and she asks him to pretend that they're back together because he's the only boyfriend she's ever had that her father likes.
|410||The Alien Parasite Hypothesis||December 9, 2010|
|411||The Justice League Recombination||December 16, 2010||
The guys discover that Penny and her ex boyfriend, Zack, are back together. Much to Penny's annoyance, she and Zack end up going to the comic book store New Year's Eve party as Wonder Woman and Superman.
|412||The Bus Pants Utilization||January 6, 2011||
Sheldon, Howard, and Raj are eating together in the Cafeteria when Leonard approaches them with an idea for a smartphone app that helps users solve Differential Equations. Leonard quickly recruits Howard, Raj, and reluctantly Sheldon who becomes too obnoxious and gets bumped from the team.
|413||The Love Car Displacement||January 20, 2011||
Leonard, Sheldon, Howard, Raj, Amy, and Bernadette are invited to be on a discussion panel at a symposium in San Francisco. Amy invites Penny as her guest which results in muliple hotel room bed hopping.
|414||The Thespian Catalyst||February 3, 2011|
|415||The Benefactor Factor||February 10, 2011|
|416||The Cohabitation Formulation||February 17, 2011|
|417||The Toast Derivation||February 24, 2011||
Sheldon is upset when he realizes Leonard is the center of their group of friends. When the gang starts hanging out at Raj's, Sheldon decides, on advice of Amy and Penny, to get a new group of friends, which consists of Kripke, Stuart, Zack, and LeVar Burton.
|418||The Prestidigitation Approximation||March 10, 2011|
|419||The Zarnecki Incursion||March 31, 2011|
|420||The Herb Garden Germination||April 7, 2011||Mark Cendrowski|
|421||The Agreement Dissection||April 28, 2011||Mark Cendrowski|
|422||The Wildebeest Implementation||May 5, 2011||Mark Cendrowski|
|423||The Engagement Reaction||May 12, 2011||Howard Murray|
|424||The Roommate Transmogrification||May 19, 2011||Mark Cendrowski||
Leonard and Priya decide to live together in Raj's Apartment, while Raj can become Sheldon's room mate. Sheldon is very happy after Raj prepares dinner for them. Penny and Raj get drunk together and very close.