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).

Season episodes list 4

S04E01

S04E01 : The Robotic Manipulation 8.64/10 (aired on 09/23/2010)

Penny tags along on Sheldon's first ever date; Wolowitz finds a new use for a robotic arm.
S04E02

S04E02 : The Cruciferous Vegetable Amplification 8.37/10 (aired on 09/30/2010)

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon…
S04E03

S04E03 : The Zazzy Substitution 8.01/10 (aired on 10/07/2010)

The guys are concerned as Sheldon searches for an alternative to human companionship.
S04E04

S04E04 : The Hot Troll Deviation 8.09/10 (aired on 10/14/2010)

An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work.
S04E05

S04E05 : The Desperation Emanation 7.84/10 (aired on 10/21/2010)

Leonard realizes he’s the only one without a girlfriend, while Sheldon wants to get rid of his.
S04E06

S04E06 : The Irish Pub Formulation 8.12/10 (aired on 10/28/2010)

Leonard keeps an affair a secret from Sheldon, Howard and Raj.
S04E07

S04E07 : The Apology Insufficiency 8.19/10 (aired on 11/04/2010)

Sheldon's answers during an FBI interview put Wolowitz's security clearance in jeopardy.
S04E08

S04E08 : The 21-Second Excitation 8.21/10 (aired on 11/11/2010)

While the guys camp in line for a long-awaited movie screening, Penny and Bernadette invite Amy to…
S04E09

S04E09 : The Boyfriend Complexity 8.47/10 (aired on 11/18/2010)

Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a…
S04E10

S04E10 : The Alien Parasite Hypothesis 7.84/10 (aired on 12/09/2010)

Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who…
S04E11

S04E11 : The Justice League Recombination 8.65/10 (aired on 12/16/2010)

The guys find a "super" use for Penny's new boyfriend, Zack, when they enter a costume contest as…
S04E12

S04E12 : The Bus Pants Utilization 7.74/10 (aired on 01/06/2011)

Leonard's idea for a smartphone app derails his friendship with Sheldon.
S04E13

S04E13 : The Love Car Displacement 8.3/10 (aired on 01/20/2011)

Bernadette runs into her ex-boyfriend while attending a science event with Wolowitz.
S04E14

S04E14 : The Thespian Catalyst 7.92/10 (aired on 02/03/2011)

Hoping it will make him a better teacher, Sheldon has Penny give him acting lessons. Raj has…
S04E15

S04E15 : The Benefactor Factor 7.88/10 (aired on 02/10/2011)

A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of…
S04E16

S04E16 : The Cohabitation Formulation 8.04/10 (aired on 02/17/2011)

As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his…
S04E17

S04E17 : The Toast Derivation 8.04/10 (aired on 02/24/2011)

Sheldon becomes concerned when everybody begins to hang out at Raj's apartment and discovers…
S04E18

S04E18 : The Prestidigitation Approximation 8.23/10 (aired on 03/10/2011)

Sheldon is baffled by Wolowitz's magic trick. Meanwhile, Leonard realizes dating Priya may make it…
S04E19

S04E19 : The Zarnecki Incursion 8.12/10 (aired on 03/31/2011)

Sheldon's World of Warcraft online game account is hacked and he is determined to find out who did…
S04E20

S04E20 : The Herb Garden Germination 8.31/10 (aired on 04/07/2011)

Sheldon and Amy decide to start several rumors about the others as a test. Meanwhile, Howard takes…
S04E21

S04E21 : The Agreement Dissection 8.29/10 (aired on 04/28/2011)

When Leonard spends too much time in the shower with Priya, Sheldon charges Leonard with two…
S04E22

S04E22 : The Wildebeest Implementation 7.94/10 (aired on 05/05/2011)

Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and…
S04E23

S04E23 : The Engagement Reaction 8.12/10 (aired on 05/12/2011)

When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the…
S04E24

S04E24 : The Roommate Transmogrification 8.58/10 (aired on 05/19/2011)

When Bernadette receives her PhD, Wolowitz feels emasculated. Raj and Leonard swap places and Penny…