Season 4

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).

1. 

   1. The Robotic Manipulation

   2010-09-23 · 21m

   Penny tags along on Sheldon's first ever date; Wolowitz finds a new use for a robotic arm.

2. 

   2. The Cruciferous Vegetable Amplification

   2010-09-30 · 21m

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

3. 

   3. The Zazzy Substitution

   2010-10-07 · 21m

   The guys are concerned as Sheldon searches for an alternative to human companionship.

4. 

   4. The Hot Troll Deviation

   2010-10-14 · 20m

   An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work.

5. 

   5. The Desperation Emanation

   2010-10-21 · 21m

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

6. 

   6. The Irish Pub Formulation

   2010-10-28 · 22m

   Leonard keeps an affair a secret from Sheldon, Howard and Raj.

7. 

   7. The Apology Insufficiency

   2010-11-04 · 21m

   Sheldon's answers during an FBI interview put Wolowitz's security clearance in jeopardy.

8. 

   8. The 21-Second Excitation

   2010-11-11 · 19m

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

9. 

   9. The Boyfriend Complexity

   2010-11-18 · 21m

   Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a telescope.

10. 

    10. The Alien Parasite Hypothesis

    2010-12-09 · 20m

    Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who would be the better superhero.

11. 

    11. The Justice League Recombination

    2010-12-16 · 20m

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

12. 

    12. The Bus Pants Utilization

    2011-01-06 · 21m

    Leonard's idea for a smartphone app derails his friendship with Sheldon.

13. 

    13. The Love Car Displacement

    2011-01-20 · 21m

    Bernadette runs into her ex-boyfriend while attending a science event with Wolowitz.

14. 

    14. The Thespian Catalyst

    2011-02-03 · 21m

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

15. 

    15. The Benefactor Factor

    2011-02-10 · 20m

    A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science.

16. 

    16. The Cohabitation Formulation

    2011-02-17 · 20m

    As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his relationship with Raj's sister.

17. 

    17. The Toast Derivation

    2011-02-24 · 21m

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

18. 

    18. The Prestidigitation Approximation

    2011-03-10 · 21m

    Sheldon is baffled by Wolowitz's magic trick. Meanwhile, Leonard realizes dating Priya may make it impossible to continue being friends with Penny.

19. 

    19. The Zarnecki Incursion

    2011-03-31 · 21m

    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 various things and more adventurous boyfriend... for some other woman — Priya.

20. 

    20. The Herb Garden Germination

    2011-04-07 · 21m

    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.

21. 

    21. The Agreement Dissection

    2011-04-28 · 21m

    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 agreement's vague wording, much to Sheldon's dismay. When the guys take advantage of Priya's skills in order to eat Greek food on pizza night, Sheldon goes to Penny, who invites him to a girls' night out with Amy and Bernadette, which Sheldon agrees to after Penny mentions that they may be talking trash about Priya. After the girls drink some cocktails, they decide to take Sheldon dancing, which Sheldon reluctantly goes along with. After dancing, Sheldon takes an intoxicated Amy back to her apartment and as well as talking about Priya, meets a monkey who is addicted to smoking cigarettes. Amy tells Sheldon not to give in to Priya's law skills, before kissing him and going to her bathroom to vomit.

22. 

    22. The Wildebeest Implementation

    2011-05-05 · 21m

    Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.

23. 

    23. The Engagement Reaction

    2011-05-12 · 20m

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

24. 

    24. The Roommate Transmogrification

    2011-05-19 · 21m

    When Bernadette receives her PhD, Wolowitz feels emasculated. Raj and Leonard swap places and Penny does something she's regrets.