The Big Bang Theory

The Big Bang Theory Season 1 Episodes

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Season 1 Episode Guide

Episode 1 - Season 1, Episode 1: Pilot

Meet two brainiacs with a lot to learn. Leonard and Sheldon can tell their quarks from their quantum physics, but have no clue how women add up. Leave it to their pretty new neighbor, just off a messy breakup, to teach them a thing or two.

                                                                                                                                                                                                                                                                                                                                                                                                                                

Episode 1 - Pilot

Meet two brainiacs with a lot to learn. Leonard and Sheldon can tell their quarks from their quantum physics, but have no clue how women add up. Leave it to their pretty new neighbor, just off a messy breakup, to teach them a thing or two.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

Episode 2 - Season 1, Episode 2: The Big Bran Hypothesis

After Leonard tries to do a favor for Penny, Sheldon ruins the plan. Leonard volunteers to sign for a package, hoping to make a good impression on Penny.

  

Episode 2 - The Big Bran Hypothesis

After Leonard tries to do a favor for Penny, Sheldon ruins the plan. Leonard volunteers to sign for a package, hoping to make a good impression on Penny.

  

Episode 3 - The Fuzzyboots Corollary

When Leonard sees Penny kissing a guy in front of her apartment door he is devastated. The guys convince him to ask someone out at work, but when he tries and is brutally turned down by a geeky girl, he is even more depressed.

  

Episode 3 - Season 1, Episode 3: The Fuzzyboots Corollary

When Leonard sees Penny kissing a guy in front of her apartment door he is devastated. The guys convince him to ask someone out at work, but when he tries and is brutally turned down by a geeky girl, he is even more depressed.

  

Episode 4 - Season 1, Episode 4: The Luminous Fish Effect

After being fired from his job, Sheldon attempts to explore the "dreadful" life beyond physics. But his initial thrill of shopping with Penny devolves over time to him weaving ponchos as a shut-in, forcing Leonard to call on Sheldon's mother, Mary (Laurie Metcalf - Roseanne ).

  

Episode 4 - The Luminous Fish Effect

After being fired from his job, Sheldon attempts to explore the "dreadful" life beyond physics. But his initial thrill of shopping with Penny devolves over time to him weaving ponchos as a shut-in, forcing Leonard to call on Sheldon's mother, Mary (Laurie Metcalf - "Roseanne").

  

Episode 5 - Season 1, Episode 5: The Hamburger Postulate

After sensing that his pursuit of Penny isn't going anywhere, Leonard agrees to an unexpected sexual encounter with fellow scientist Leslie Winkle (recurring guest star Sara Gilbert). The one-night stand throws Leonard and Sheldon deep into uncharted social waters.

  

Episode 5 - The Hamburger Postulate

After sensing that his pursuit of Penny isn't going anywhere, Leonard agrees to an unexpected sexual encounter with fellow scientist Leslie Winkle (recurring guest star Sara Gilbert). The one-night stand throws Leonard and Sheldon deep into uncharted social waters.

  

Episode 6 - The Middle Earth Paradigm

The socially stunted guys are nervous when Penny invites them to a party she's hosting.

  

Episode 6 - Season 1, Episode 6: The Middle Earth Paradigm

The socially stunted guys are nervous when Penny invites them to a party she's hosting.

  

Episode 7 - Season 1, Episode 7: The Dumpling Paradox

When Wolowitz seduces Penny's friend and ends up sleeping with her in Penny's apartment, Penny sleeps on Leonard and Sheldon's couch.

  

Episode 7 - The Dumpling Paradox

When Wolowitz seduces Penny's friend and ends up sleeping with her in Penny's apartment, Penny sleeps on Leonard and Sheldon's couch.

  

Episode 8 - The Grasshopper Experiment

Koothrappali becomes overwhelmed when his parents arrange a blind date for him, but he discovers he actually can talk to a member of the opposite sex after a few drinks.

  

Episode 8 - Season 1, Episode 8: The Grasshopper Experiment

Koothrappali becomes overwhelmed when his parents arrange a blind date for him, but he discovers he actually can talk to a member of the opposite sex after a few drinks.

  

Episode 9 - The Cooper-Hofstadter Polarization

Sheldon and Leonard are invited to present their joint findings at a physics conference, but Sheldon refuses.

  

Episode 9 - Season 1, Episode 9: The Cooper-Hofstadter Polarization

Sheldon and Leonard are invited to present their joint findings at a physics conference, but Sheldon refuses.

  

Episode 10 - Season 1, Episode 10: The Loobenfeld Decay

After hearing Penny sing, Leonard lies to avoid seeing her perform. Sheldon goes one step further with a more elaborate lie, leading to the appearance of his nonexistent cousin. D.J. QUALLS ( Road Trip ) guest stars.

  

Episode 10 - The Loobenfeld Decay

After hearing Penny sing, Leonard lies to avoid seeing her perform. Sheldon goes one step further with a more elaborate lie, leading to the appearance of his nonexistent cousin. D.J. QUALLS ("Road Trip") guest stars.

  

Episode 11 - The Pancake Batter Anomaly

Sheldon gets sick and Penny has to deal with him.

  

Episode 11 - Season 1, Episode 11: The Pancake Batter Anomaly

Sheldon gets sick and Penny has to deal with him.

  

Episode 12 - Season 1, Episode 12: The Jerusalem Duality

When Leonard and Sheldon meet a teenage physics prodigy, Sheldon is distraught that the boy genius is younger and smarter, and crafts a plan to derail the young prodigy's research.

  

Episode 12 - The Jerusalem Duality

When Leonard and Sheldon meet a teenage physics prodigy, Sheldon is distraught that the boy genius is younger and smarter, and crafts a plan to derail the young prodigy's research.

  

Episode 13 - The Bat Jar Conjecture

The guys kick Sheldon off the team for the Physics Bowl and enlist his nemesis Leslie Winkle (recurring guest star Sara Gilbert) to take his place.

  

Episode 13 - Season 1, Episode 13: The Bat Jar Conjecture

The guys kick Sheldon off the team for the Physics Bowl and enlist his nemesis Leslie Winkle (recurring guest star Sara Gilbert) to take his place.

  

Episode 14 - The Nerdvana Annihilation

When the guys buy a time-machine prop from a classic movie, Penny's reaction forces Leonard to take a hard look at his life.

  

Episode 14 - Season 1, Episode 14: The Nerdvana Annihilation

When the guys buy a time-machine prop from a classic movie, Penny's reaction forces Leonard to take a hard look at his life.

  

Episode 15 - The Shiksa Indeterminacy

Leonard, Wolowitz, and Koothrappali all become smitten with Sheldon's twin sister, Missy (guest star Courtney Henggeler), and Leonard devises a plan to eliminate his rivals. The plan backfires, however, when Sheldon declares he will decide whom his sister dates.

  

Episode 15 - Season 1, Episode 15: The Shiksa Indeterminacy

Leonard, Wolowitz, and Koothrappali all become smitten with Sheldon's twin sister, Missy (guest star Courtney Henggeler), and Leonard devises a plan to eliminate his rivals. The plan backfires, however, when Sheldon declares he will decide whom his sister dates.

  

Episode 16 - Season 1, Episode 16: The Peanut Reaction

When Penny learns that Leonard doesn't celebrate birthdays, she attempts to throw him a surprise party; she is sidetracked by Sheldon, however, who unexpectedly gets to live out one of his greatest fantasies at an electronics store.

  

Episode 16 - The Peanut Reaction

When Penny learns that Leonard doesn't celebrate birthdays, she attempts to throw him a surprise party; she is sidetracked by Sheldon, however, who unexpectedly gets to live out one of his greatest fantasies at an electronics store.

  

Episode 17 - The Tangerine Factor

When Penny breaks up with her boyfriend, Leonard finally gets up the courage to ask her out on a real date. When she says yes, each seeks the "wisdom" of a reluctant advisor - Sheldon.

  

Episode 17 - Season 1, Episode 17: The Tangerine Factor

When Penny breaks up with her boyfriend, Leonard finally gets up the courage to ask her out on a real date. When she says yes, each seeks the "wisdom" of a reluctant advisor - Sheldon.

  

Episode 18 - Season 2, Episode 1: The Bad Fish Paradigm

In the second season premiere, after her first date with Leonard goes awry, Penny finds an unwilling confidant in Leonard's anti-social roommate, Sheldon.

  

Episode 19 - Season 2, Episode 2: The Codpiece Topology

Penny and Leonard compete to see who will be the first to move on after their breakup. When Leonard sees Penny with a handsome new guy (guest star TRAVIS SCHULDT -- Scrubs), he enters into a rebound relationship with Sheldon's nemesis, Leslie Winkle (series regular SARA GILBERT).

  

Episode 20 - Season 2, Episode 3: The Barbarian Sublimination

Sheldon creates a monster when he introduces Penny to the world of online gaming. Especially when her addiction wreaks havoc on his life.

  

Episode 21 - Season 2, Episode 4: The Griffin Equivalency

Raj's ego puts all of his friendships in jeopardy when he gets an inflated sense of self. Newly famous because of an article in a magazine, Raj (series regular KUNAL NAYYAR) makes a disastrous play for Leonard's longtime crush Penny.

  

Episode 22 - Season 2, Episode 5: The Euclid Alternative

Leonard and his friends stage an intervention to make Sheldon confront his longstanding fear of driving.

  

Episode 23 - Season 2, Episode 6: The Cooper-Nowitzki Theorem

A young grad student's attraction to Sheldon confuses everyone including Sheldon himself.

  

Episode 24 - Season 2, Episode 7: The Panty Pinata Polarization

Sheldon and Penny engage in a battle of wills as Penny vows to get revenge on Sheldon when he bans her from the apartment for a series of petty infractions.

  

Episode 25 - Season 2, Episode 8: The Lizard-Spock Expansion

Wolowitz (series regular SIMON HELBERG) thinks he's found the love of his life (guest star SARA RUE), until she meets Leonard.

  

Episode 26 - Season 2, Episode 9: The White Asparagus Triangulation

Sheldon can barely contain his joy when Leonard starts dating a woman (Sara Rue) who meets Sheldon's exacting standards.

  

Episode 27 - Season 2, Episode 10: The Vartabedian Conundrum

Leonard just can't say no. When his relationship with new girlfriend, Stephanie starts moving too fast, Leonard turns to Penny for advice.

  

Episode 28 - Season 2, Episode 11: The Bath Item Gift Hypothesis

Leonard's handsome colleague starts dating Penny. And Leonard's friends are being tormented by Sheldon's obsession with gift-giving etiquette.

  

Episode 29 - Season 2, Episode 12: The Killer Robot Instability

When Penny's comment about Wolowitz's love life sends him into a depressed stupor, his friends lose their most important teammate in an upcoming fighting robot competition.

  

Episode 30 - Season 2, Episode 13: The Friendship Algorithm

Socially awkward Sheldon develops a scientific procedure for making friends.

  

Episode 31 - Season 2, Episode 14: The Financial Permeability

Sheldon's "simple" solution to Penny's financial problem leads to a confrontation between Leonard and Penny's hulking ex-boyfriend, Kurt (guest star Brian Patrick Wade).

  

Episode 32 - Season 2, Episode 15: The Maternal Capacitance

A disastrous visit from Mrs. Hofstadter (special guest star Christine Baranski) brings Leonard and Penny closer together.

  

Episode 33 - Season 2, Episode 16: The Cushion Saturation

A paintball game has surprising consequences for Leonard and his friends when it leads to a fight between Penny and Sheldon and romance for Wolowitz and Leslie.

  

Episode 34 - Season 2, Episode 17: The Terminator Decoupling

A train trip to San Francisco takes a major detour when Leonard, Sheldon, Wolowitz and Raj discover that beautiful sci-fi actress Summer Glau ( Terminator ) is onboard.

  

Episode 35 - Season 2, Episode 18: The Work Song Nanocluster

Penny's home hair products business becomes a complete nightmare when a caffeine-addled Sheldon takes over.

  

Episode 36 - Season 2, Episode 19: The Dead Hooker Juxtaposition

There's a new queen bee in the building! Penny develops a rivalry with a sexy female neighbor moves in to the building and threatens to become the "new Penny".

  

Episode 37 - Season 2, Episode 20: The Hofstadter Isotope

While Stuart (guest star Kevin Sussman), a fellow comic book-loving pal of the guys, romances Penny, Leonard and Wolowitz venture out into the world of Ladies' Night at a local bar.

  

Episode 38 - Season 2, Episode 21: The Vegas Renormalization

Leonard and Koothrappali take a heartbroken Wolowitz to Las Vegas, leaving Sheldon locked out of his apartment and forced to bunk with Penny.

  

Episode 39 - Season 2, Episode 22: The Classified Materials Turbulence

Things begin to look up for Leonard when Penny makes a surprising revelation on her second date with Stuart (guest star Kevin Sussman). Meanwhile, Wolowitz enlists his friends' help when he discovers a critical design flaw in his project for NASA.

  

Episode 40 - Season 2, Episode 23: The Monopolar Expedition

On the second season finale, Leonard and Penny reconsider their feelings for one another. When Leonard and his friends decide to spend the summer working at the North Pole, Penny is conflicted.

  

Episode 41 - Season 3, Episode 1: The Electric Can Opener Fluctuation

On the third season premiere, Sheldon (series star Jim Parsons) flees back to Texas in disgrace when he learns that the guys tampered with his arctic expedition data – forcing his friends to follow him, and threatening Leonard's (series star Johnny Galecki), hopes for a romantic encounter with Penny (series star Kaley Cuoco).

  

Episode 42 - Season 3, Episode 2: The Jiminy Conjecture

Leonard and Penny struggle to recover from an awkward first hookup, while Sheldon and Howard (series star Simon Helberg) stake their best comic books on a bet to determine the species of a cricket. Lewis Black guest stars as an entymologist who settles the high-stakes bet.

  

Episode 43 - Season 3, Episode 3: The Gothowitz Deviation

Howard and Raj (series star Kunal Nayyar) visit a Goth nightclub to pick up women, while Sheldon attempts to build a better Penny using chocolate-based behavior modification.

  

Episode 44 - Season 3, Episode 4: The Pirate Solution

Raj must find a new job or be sent back to India. Sheldon, however, has a solution – which leaves Leonard and Penny dealing with Howard as third wheel.

  

Episode 45 - Season 3, Episode 5: The Creepy Candy Coating Corollary

While Sheldon settles a score with his nemesis, Star Trek: The Next Generation's Wil Wheaton (guest starring as himself), Wolowitz begs Leonard to get Penny to set him up with one of her friends.

  

Episode 46 - Season 3, Episode 6: The Cornhusker Vortex

Sheldon teaches Leonard how to understand football, while a kite-fighting incident threatens Howard and Raj's friendship.

  

Episode 47 - Season 3, Episode 7: The Guitarist Amplification

Sheldon plays the peacemaker when an argument between Leonard and Penny proves “inconvenient” to him.

  

Episode 48 - Season 3, Episode 8: The Adhesive Duck Deficiency

With Leonard, Howard and Raj away camping in the desert, an injured Penny has only Sheldon to rely on.

  

Episode 49 - Season 3, Episode 9: The Vengeance Formulation

After he's humiliated on National Public Radio, Sheldon vows to destroy Kripke (guest star John Ross Bowie), and the guys help, Sheldon exact his revenge. Meanwhile, Wolowitz tries not to destroy his new relationship with Bernadette (guest star Melissa Rauch). Katee Sackhoff (Battlestar Galactica) makes a cameo as Wolowitz’s dream girl.

  

Episode 50 - Season 3, Episode 10: The Gorilla Experiment

Sheldon takes on his greatest challenge when he attempts to help Penny understand physics, and Wolowitz becomes jealous when Leonard starts hanging out with his new girlfriend.

  

Episode 51 - Season 3, Episode 11: The Maternal Congruence

A visit from Leonard's mother (guest star Christine Baranski) delights Sheldon and horrifies Leonard.

  

Episode 52 - Season 3, Episode 12: The Psychic Vortex

While Sheldon and Koothrappali attend a university mixer, Leonard is upset to discover that Penny believes in psychics. Danica McKellar (The Wonder Years) guest stars as the object of Raj’s attraction.

  

Episode 53 - Season 3, Episode 13: The Bozeman Reaction

When their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system – and Sheldon struggles to cope.

  

Episode 54 - Season 3, Episode 14: The Einstein Approximation

Suffering from a case of physicists block, Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.

  

Episode 55 - Season 3, Episode 15: The Large Hadron Collision

Its Valentines Day, and Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider (the world's largest and highest energy particle accelerator) in Switzerland. Will it be Sheldon or Penny?

  

Episode 56 - Season 3, Episode 16: The Excelsior Acquisition

Sheldon misses his chance to meet comic book legend STAN LEE (as himself) when he winds up in traffic court after he gets a ticket, because of Penny.

  

Episode 57 - Season 3, Episode 17: The Precious Fragmentation

When the guys find a rare movie prop ring from The Lord of the Rings at a garage sale, it threatens to tear them apart - forcing them to choose the ring or their friendship.

  

Episode 58 - Season 3, Episode 18: The Pants Alternative

Sheldon's friends come to his aid when his fear of public speaking stands between him and a coveted award.

  

Episode 59 - Season 3, Episode 19: The Wheaton Recurrence

A fight between Leonard and Penny threatens their relationship, while Sheldon battles WIL WHEATON (guest starring as Himself) in bowling.

  

Episode 60 - Season 3, Episode 20: The Spaghetti Catalyst

When Leonard and Penny aren't speaking, Sheldon goes to extremes to keep them both happy and gets caught in a lie.

  

Episode 61 - Season 3, Episode 21: The Plimpton Stimulation

Leonard and Sheldon compete for the attention of a famous female physicist - Dr. Elizabeth Plimpton (guest star JUDY GREER).

  

Episode 62 - Season 3, Episode 22: The Staircase Implementation

Leonard tells Penny the story of how he met Sheldon for the first time...and what happened to the elevator.

  

Episode 63 - Season 3, Episode 23: The Lunar Excitation

In the third season finale, Wolowitz and Koothrappali search for Sheldon's perfect match online - and find Sheldon's ideal woman (guest star MAYIM BIALIK). Meanwhile, Penny worries that dating Leonard has ruined her for normal guys.

  

Episode 64 - Season 4, Episode 1: The Robotic Manipulation

On the fourth season premiere, Penny (series star KALEY CUOCO) finds herself along for the ride on Sheldon's (series star JIM PARSONS) first date ever. Meanwhile, Wolowitz (series star SIMON HELBERG) finds a new use for a robotic arm. MAYIM BIALIK guest stars as Sheldon's date, Amy Fowler.

  

Episode 65 - Season 4, Episode 2: The Cruciferous Vegetable Amplification

When Sheldon realizes he won't live long enough to download his consciousness into a robot body, he attempts to extend his lifespan. Apple Co-Founder STEVE WOZNIAK guest stars as Himself.

  

Episode 66 - Season 4, Episode 3: The Zazzy Substitution

The guys are concerned as Sheldon searches for an alternative to human companionship after he and Amy (MAYIM BIALIK) break up. LAURIE METCALF reprises her role as Sheldon's mother.

  

Episode 67 - Season 4, Episode 4: The Hot Troll Deviation

An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work. Battlestar Galactica's KATEE SACKHOFF and Star Trek's GEORGE TAKEI guest star as themselves as Wolowitz's love gurus. MELISSA RAUCH reprises her role as Howard's girlfriend, Bernadette.

  

Episode 68 - Season 4, Episode 5: The Desperation Emanation

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

  

Episode 69 - Season 4, Episode 6: The Irish Pub Formulation

A visit from Raj's sister (guest star AARTI MANKAD) creates tension among the guys - especially when Leonard keeps an affair secret from Sheldon, Howard and Raj.

  

Episode 70 - Season 4, Episode 7: The Apology Insufficiency

When an FBI agent (guest star ELIZA DUSHKU) interviews the guys for Wolowitz's security clearance, Sheldon's answers during the screening put Wolowitz's clearance in jeopardy.

  

Episode 71 - Season 4, Episode 8: The 21-Second Excitation

When the guys camp in line for a screening, their plans are thwarted by Sheldon's greatest nemesis, WIL WHEATON (guest starring as himself). Meanwhile, Penny and Bernadette invite Amy to her first slumber party.

  

Episode 72 - Season 4, Episode 9: The Boyfriend Complexity

Penny asks Leonard to lie to her father, Wyatt (guest star KEITH CARRADINE), while Howard, Raj and Bernadette pull an all-nighter at a telescope.

  

Episode 73 - Season 4, Episode 10: The Alien Parasite Hypothesis

Amy finds she has sexual feelings for Penny's ex, Zack (guest star BRIAN THOMAS SMITH) while Koothrappali and Wolowitz try to prove who would be the better superhero.

  

Episode 74 - Season 4, Episode 11: The Justice League Recombination

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

  

Episode 75 - Season 4, Episode 12: The Bus Pants Utilization

Leonard's idea for a smartphone app derails his friendship with Sheldon as they fight for control of the project.

  

Episode 76 - Season 4, Episode 13: The Love Car Displacement

Tension runs high when everyone is staying at the same hotel for a science event and Bernadette runs into her ex-boyfriend (guest star RICK FOX three-time NBA champion with the Los Angeles Lakers).

  

Episode 77 - Season 4, Episode 14: The Thespian Catalyst

Sheldon wants Penny to give him acting lessons, hoping that they will help him become a better teacher. Meanwhile, Koothrappali fantasizes about his best friend's girlfriend.

  

Episode 78 - Season 4, Episode 15: The Benefactor Factor

A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science. JESSICA WALTER (Arrested Development) guest stars as the widowed benefactress and JOSHUA MALINA (The West Wing) guest stars as the University President.

  

Episode 79 - Season 4, Episode 16: The Cohabitation Formulation

As Wolowitz contemplates taking things with Bernadette to the next level, he must choose between his girlfriend and his mother. Meanwhile, Leonard rekindles his relationship with Raj's sister, Priya.

  

Episode 80 - Season 4, Episode 17: The Toast Derivation

When the gang starts hanging out at Raj's and Sheldon realizes it's actually Leonard who is the center of their social group, Sheldon decides to get a new group of friends.

  

Episode 81 - Season 4, Episode 18: The Prestidigitation Approximation

Leonard must choose between his new girlfriend, Priya, and his friendship with Penny. Meanwhile, Howard drives Sheldon crazy with a magic trick.

  

Episode 82 - Season 4, Episode 19: The Zarnecki Incursion

When someone hacks Sheldon's online gaming account, the guys go on a quest to find the culprit.

  

Episode 83 - Season 4, Episode 20: The Herb Garden Germination

Sheldon and Amy experiment on their friends by spreading gossip, while Howard takes a big step in his relationship with Bernadette.

  

Episode 84 - Season 4, Episode 21: The Agreement Dissection

Priya uses her lawyer skills to pick apart the roommate agreement...and put Sheldon in his place. Meanwhile, the girls take Sheldon dancing.

  

Episode 85 - Season 4, Episode 22: The Wildebeest Implementation

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

  

Episode 86 - Season 4, Episode 23: The Engagement Reaction

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

  

Episode 87 - Season 4, Episode 24: The Roomate Transmorgrification

When Bernadette receives her Ph.D., the guys take joy in reminding an emasculated Wolowitz that he is the only one in their group who isn't a doctor. Meanwhile, Koothrappali becomes Sheldon's new roommate after hearing Leonard and Priya engaging in a Star Trek bedroom fantasy, on the fourth season finale.

  

Episode 88 - Season 5, Episode 1: The Skank Reflex Analysis

The fifth season premiere picks up where the fourth season finale left off as the gang deals with the aftermath of Penny and Raj's night together. While Penny worries that she's screwed things up permanently with her friends, Sheldon takes command of the paintball team. Emmy® nominee CHRISTINE BARANSKI (The Good Wife) reprises her role as Leonard's emotionally distant mother.

  

Episode 89 - Season 5, Episode 2: The Infestation Hypothesis

A battle of wills between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya (recurring guest star AARTI MANN), who has moved back to India.

  

Episode 90 - Season 5, Episode 3: The Pulled Groin Extrapolation

Leonard attends a co-worker's wedding as Amy's date. Meanwhile, Howard tries to convince Bernadette to live with his mom after they get married by suggesting a trial run with the two of them staying with his mom over the weekend.

  

Episode 91 - Season 5, Episode 4: The Wiggly Finger Catalyst

When Raj is upset he's the only one of the four guys who is not in a relationship, Penny sets out to find the perfect date, introducing him to Emily (guest star KATIE LeCLERC Switched at Birth) a girl he can actually talk to!

  

Episode 92 - Season 5, Episode 5: The Russian Rocket Reaction

Sheldon's old nemesis, WIL WHEATON (guest starring as Himself), returns and invites everyone to a housewarming party. Sheldon threatens to "defriend" Leonard if he attends. But when he hears that BRENT SPINER (guest starring as Himself), the actor who played Commander Data, will be there, Sheldon decides to go to the party after all... only to discover new levels of treachery. Meanwhile, Howard gets an out-of-this-world opportunity that Bernadette reacts to strongly.

  

Episode 93 - Season 5, Episode 6: The Rhinitis Revelation

Craving a little motherly love, Sheldon competes with the gang for his mother’s attention when she comes to visit. LAURIE METCALF reprises her role as Sheldon’s mother, Mary.

  

Episode 94 - Season 5, Episode 7: The Good Guy Fluctuation

A cute comic book artist (guest star COURTNEY FORD) puts Leonard's relationship with Priya to the test; while Sheldo, getting into the spirit of Halloween, tries to scare the guys.

  

Episode 95 - Season 5, Episode 8: The Isolation Permutation

Amy is heartbroken when Bernadette and Penny go shopping for wedding dresses without her.

  

Episode 96 - Season 5, Episode 9: The Ornithophobia Diffusion

Can friends with benefits still be friends without? Leonard and Penny try hanging out alone, while Sheldon must overcome his fear of birds.

  

Episode 97 - Season 5, Episode 10: The Flaming Spittoon Acquisition

Sheldon becomes jealous and considers taking his relationship with Amy to the next level when Stuart (guest star KEVIN SUSSMAN) from the comic book store asks her out on a date.

  

Episode 98 - Season 5, Episode 11: The Speckerman Recurrence

Leonard must face his fears after being contacted by his high school tormentor (guest star LANCE BARBER), while Penny realizes that she might have been a bully herself.

  

Episode 99 - Season 5, Episode 12: The Shiny Trinket Maneuver

Sheldon gets in trouble with Amy when he isn't impressed by her recent accomplishment, and it's up to Penny to teach him how to be a better boyfriend. Howard, meanwhile, must come to grips with Bernadette's dislike of children.

  

Episode 100 - Season 5, Episode 13: The Recombination Hypothesis

The possibility of Leonard and Penny getting back together could prove disastrous when Leonard offers Penny a spur of the moment invitation to a romantic dinner for two on the 100th episode of the series.

  

Episode 101 - Season 5, Episode 14: The Beta Test Initiation

Leonard and Penny experiment with dating again by "beta testing" their relationship, while Raj develops a peculiar relationship with his phone's virtual assistant.

  

Episode 102 - Season 5, Episode 15: The Friendship Contraction

Sheldon's selfish demands force Leonard to reconsider their friendship. Could this be the end of The Roommate Agreement? Meanwhile, Howard tries to pick his astronaut nickname, but NASA astronaut MIKE MASSIMINO (guest starring as himself) has other ideas.

  

Episode 103 - Season 5, Episode 16: The Vacation Solution

When Sheldon is forced to take a vacation by the university, he goes to work with Amy in her neurobiology lab. Meanwhile, Bernadette wants Howard to sign a pre-nuptial agreement.

  

Episode 104 - Season 5, Episode 17: The Rothman Disintegration

When a corner office at the University opens up, Sheldon must compete for it with his office nemesis, Barry Kripke.

  

Episode 105 - Season 5, Episode 18: The Werewolf Transformation

Sheldon's life is turned upside-down after his barber becomes hospitalized. Now, that there's been a change in his routine, Sheldon finds himself re-evaluating his entire life. Meanwhile, astronaut training causes Howard to rethink his decision to go into space.

  

Episode 106 - Season 5, Episode 19: The Weekend Vortex

It's on…like Alderaan, when the guys plan a weekend Star Wars gaming marathon! But when Sheldon chooses the guys-only weekend over a weekend with Amy to visit her aunt, he is destined to feel the force!

  

Episode 107 - Season 5, Episode 20: The Transporter Malfunction

It's a dream come true for Sheldon when he has a close encounter with his hero, Mr. Spock. Legendary sci-fi icon LEONARD NIMOY guest stars, lending his voice to a unique reprisal of his three-time Emmy®-nominated Star Trek role.

  

Episode 108 - Season 5, Episode 21: The Hawking Excitation

When Wolowitz gets tow work with world-renowned scientist STEPHEN HAWKING (guest starring as Himself), Sheldon is willing to do anything to meet his hero.

  

Episode 109 - Season 5, Episode 22: The Stag Convergence

Howard's wedding plans are in jeopardy after the guys (and Wil Wheaton) throw him a bachelor party. After details of his sexual history are leaked online, Bernadette reconsiders marrying Howard.

  

Episode 110 - Season 5, Episode 23: The Launch Acceleration

When NASA reschedules Howard's mission and puts his wedding plans in jeopardy, he's forced to face his fears and Bernadette's dad (guest star Casey Sander). Meanwhile, Leonard says something surprising to Penny in the bedroom.

  

Episode 111 - Season 5, Episode 24: The Countdown Reflection

Howard Wolowitz crosses over into the final frontiers of space…and marriage on the fifth season finale. When Howard and Bernadette decide they want to be married before his NASA space launch, the gang rushes to put on a wedding. NASA Astronaut Mike Massimino guest stars as Himself.

  

Episode 112 - Season 6, Episode 1: The Date Night Variable

On the sixth season premiere, Howard discovers that he can't escape his mother – even in space! Caught in an argument between Bernadette and his mom (recurring guest voice CAROL ANN SUSI), Howard deals with woman trouble from the International Space Station. Back on earth, meanwhile, Raj faces his loneliness, by turning his existence as a third wheel into an art form.

  

Episode 113 - Season 6, Episode 2: The Decoupling Fluctuation

When Sheldon learns that Penny is thinking about breaking up with Leonard, he tries to intervene. But Sheldon is no good at keeping secrets. Meanwhile, Howard is being picked on in space by the other astronauts (guest stars PASHA LYCHNIKOFF and MIKE MASSIMINO).

  

Episode 114 - Season 6, Episode 3: The Higgs Boson Observation

While the pressures of being in space starts to take its toll on Howard, Amy feels threatened when Sheldon hires a young female assistant, Alex (guest star MARGO HARSHMAN).

  

Episode 115 - Season 6, Episode 4: The Re-Entry Minimization

When Howard returns from space, he doesn’t get the hero’s welcome he expected. Meanwhile, Game Night turns into a battle of the sexes.

  

Episode 116 - Season 6, Episode 5: The Holographic Excitation

The gang celebrates Halloween at Stuart’s comic book store. Meanwhile Leonard and Penny discover a new spark in their relationship when he seduces her with science. And while Howard can’t stop talking about space, it takes iconic astronaut BUZZ ALDRIN (guest starring as himself) to get him grounded again.

  

Episode 117 - Season 6, Episode 6: The Extract Obilteration

Sheldon’s tenuous relationship with renowned scientist STEPHEN HAWKING is threatened by a game of “Words with Friends,” while Penny secretly enrolls in a class at the local college.

  

Episode 118 - Season 6, Episode 7: The Habitation Configuration

Pressured by Bernadette, Howard comes to terms with moving out of his mother’s house. Meanwhile, Sheldon, who’s caught in the middle of a feud between his “girlfriend” Amy and good friend WIL WHEATON, goes to Penny for advice. Star Trek’s LeVAR BURTON guest stars.

  

Episode 119 - Season 6, Episode 8: The 43 Peculiarity

Howard and Raj try to get to the bottom of why Sheldon disappears every afternoon at 2:45. Meanwhile, Leonard and Penny wrestle with jealousy in their relationship.

  

Episode 120 - Season 6, Episode 9: The Parking Spot Escalation

When the University reassigns Sheldon’s (unused) parking spot to Howard, the ensuing turf battle affects the whole gang.

  

Episode 121 - Season 6, Episode 10: The Fish Guts Displacement

Sheldon plays nursemaid to a sick Amy, while Howard attempts to bond with his father-in-law (guest star CASEY SANDER) on an upcoming fishing trip.

  

Episode 122 - Season 6, Episode 11: The Santa Simulation

Sheldon unwillingly revisits some Christmas memories during a lively game of Dungeons and Dragons, while Penny, Bernadette and Amy try to find the perfect girl for Raj when he joins the girls for ladies night.

  

Episode 123 - Season 6, Episode 12: The Egg Salad Equivalency

Sheldon is accused of sexual harassment at the University and winds up dragging Leonard, Raj and Howard into the fray. Southland’s REGINA KING guest stars as the University’s Director of Employee Relations.

  

Episode 124 - Season 6, Episode 13: The Bakersfield Expedition

While the guys take a road trip to a comic book convention in Bakersfield dressed as characters from Star Trek: The Next Generation, Leonard’s car is stolen. Meanwhile, the girls stay home and try to appreciate the world of comics.

  

Episode 125 - Season 6, Episode 14: The Cooper/Kripke Inversion

Outraged that he’s being forced to work with his university nemesis, Barry Kripke (guest star JOHN ROSS BOWIE), Sheldon faces a crisis of conscience. Meanwhile, Howard and Raj spend a thousand dollars on action figures of themselves.

  

Episode 126 - Season 6, Episode 15: The Spoiler Alert Segmentation

A fight between Leonard and Sheldon drives Leonard to finally move in with Penny – not realizing how the shift will affect Penny and Amy’s living arrangements. Meanwhile, Raj takes care of Mrs. Wolowitz while Howard is away.

  

Episode 127 - Season 6, Episode 16: The Tangible Affection Proof

While the guys try to give their significant others the perfect Valentine’s Day, Raj and Stuart throw a lonely people party at the comic book store.

  

Episode 128 - Season 6, Episode 17: The Monster Isolation

After a terrible date, Raj vows to never leave his apartment again. Meanwhile, Penny actually impresses Sheldon with her acting skills.

  

Episode 129 - Season 6, Episode 18: The Contractual Obligation Implementation

Back to school! Leonard, Sheldon and Howard try to advance the cause of women in science by speaking with junior high girls about their future careers, while Raj plans his date with Lucy (guest star KATE MICUCCI).

  

Episode 130 - Season 6, Episode 19: The Closet Reconfiguration

When Howard finds a letter from his father, he’s forced to confront his past, struggling with whether or not he should open it. And Leonard and Penny throw a “grown-up” cocktail party at the apartment.

  

Episode 131 - Season 6, Episode 20: The Tenure Turbulence

Let the battle begin! Leonard, Sheldon and Raj fight for tenure at the University – and the competition heats up when the girls get involved!

  

Episode 132 - Season 6, Episode 21: The Closure Alternative

Sheldon feels lost after one of his favorite TV shows gets canceled too soon, so Amy tries to help him get over his compulsive need for closure. Meanwhile, Raj discovers a secret about his new love interest, Lucy.

  

Episode 133 - Season 6, Episode 22: The Proton Resurgence

Sheldon and Leonard hire Professor Proton (guest star BOB NEWHART), the host of their favorite childhood TV show, to perform. Also, Howard and Bernadette run into trouble babysitting Raj’s dog.

  

Episode 134 - Season 6, Episode 23: The Love Spell Potential

When the girls’ trip to Vegas falls through, the guys invite them to play Dungeons & Dragons – causing Sheldon and Amy’s relationship to take an unexpected turn. Meanwhile, Raj and Lucy go on a very awkward date.

  

Episode 135 - Season 6, Episode 24: The Bon Voyage Reaction

When Leonard is offered an exciting new job opportunity overseas, Sheldon grows very jealous and Penny is thrown for a loop. Meanwhile, Raj pushes Lucy a little too far in their relationship on the sixth season finale.

  

Episode 136 - Season 7, Episode 1: The Hofstadter Insufficiency

On the one-hour seventh season premiere, Sheldon and Penny bond in Leonard’s absence, but it’s Sheldon’s feelings that are crushed when Leonard returns from the North Sea. Guest star REGINA KING returns as Mrs. Davis, the University’s Director of Employee Relations.

  

Episode 137 - Season 7, Episode 2: The Deception Verification

On the second part of the one-hour seventh season premiere, Raj gets consoled about his ex-girlfriend and Howard’s relationship with his mother causes an unusual threat to his masculinity. KEVIN SUSSMAN returns as Stuart, the comic book store owner.

  

Episode 138 - Season 7, Episode 3: The Scavenger Vortex

When the entire gang competes in a cutthroat scavenger hunt designed by Raj that tests their science knowledge and street smarts, it brings out the best – and worst – in everyone.

  

Episode 139 - Season 7, Episode 4: The Raiders Minimization

After Amy ruins one of Sheldon’s favorite movies – Raiders of the Lost Ark – he gets defensive, seeking revenge. Meanwhile, Leonard discovers a way to get Penny to do anything; and Raj and Stuart create online dating profiles.

  

Episode 140 - Season 7, Episode 5: The Workplace Proximity

Sheldon must decide how much “Amy time” is too much after she takes a job at his university, and their relationship is put to the test. Meanwhile, Howard finds himself sleeping on Raj’s couch after a fight with Bernadette.

  

Episode 141 - Season 7, Episode 6: The Romance Resonance

Sheldon’s latest scientific breakthrough makes him feel like a fraud – and threatens to haunt him forever. Meanwhile, Howard’s romantic gesture to Bernadette causes Penny to step up her game with Leonard.

  

Episode 142 - Season 7, Episode 7: The Proton Displacement

Sheldon feels slighted when Professor Proton (recurring guest star BOB NEWHART) seeks advice from Leonard instead of him, and he seeks revenge by befriending a rival science TV host, BILL NYE (guest starring as Himself). Meanwhile, Raj gets jealous when Howard crashes “girls’ night.”

  

Episode 143 - Season 7, Episode 8: The Itchy Brain Simulation

Leonard tries to keep Sheldon from overreacting when a past mistake comes to light, but Sheldon punishes Leonard by making him “walk a mile in his shoes.” Meanwhile, Penny confronts Raj’s ex-girlfriend, Lucy (guest star KATE MICUCCI).

  

Episode 144 - Season 7, Episode 9: The Thanksgiving Decoupling

An upset Sheldon protests when the entire gang drags him to Mrs. Wolowitz’s house for Thanksgiving. Meanwhile, Penny and Leonard must deal with a mistake from her past.

  

Episode 145 - Season 7, Episode 10: The Discovery Dissipation

Leonard and Amy help Sheldon cope with the shame he’s feeling after his accidental contribution to science is disproved. Meanwhile, Raj must stay with Howard and Bernadette for a week. IRA FLATOW guest stars as Himself.

  

Episode 146 - Season 7, Episode 11: The Cooper Extraction

While Sheldon is away in Texas, everyone gathers to decorate the apartment Christmas tree, and imagines what their lives would be like if they had never met Sheldon.

  

Episode 147 - Season 7, Episode 12: The Hesitation Ramification

When Penny’s big acting break on NCIS is a bust, Leonard struggles to help her, which results in Penny asking Leonard a bold relationship question. Meanwhile, Sheldon tries to learn how to be funny and Raj tries to work on his “game” before talking to girls.

  

Episode 148 - Season 7, Episode 13: The Occupation Recalibration

When Sheldon is forced to take a vacation, he tries to relax, but instead spends a lot of time with Penny after she quits her job. Meanwhile, Leonard struggles to be supportive of Penny and Bernadette seeks Stuart’s help in replacing one of Howard’s comic books.

  

Episode 149 - Season 7, Episode 14: The Convention Conundrum

After they guys can’t get Comic-Con tickets, Sheldon decides to hold his own convention, and winds up spending a wild night with JAMES EARL JONES (guest starring as himself). Meanwhile, the girls see if they can act like “grown-ups.” Star Wars icon CARRIE FISHER makes a cameo appearance as well.

  

Episode 150 - Season 7, Episode 15: The Locomotive Manipulation

Love is in the air when Amy convinces Sheldon to join her (as well as Howard and Bernadette) for a romantic weekend in Napa Valley to celebrate Valentine’s Day. Meanwhile, Leonard and Penny must rush Raj’s dog to the vet.

  

Episode 151 - Season 7, Episode 16: The Table Polarization

When Leonard buys a dining room table, it causes Sheldon to reevaluate the changes in his life. Meanwhile, Wolowitz is offered a chance to go back to space and Bernadette struggles with whether or not to encourage him.

  

Episode 152 - Season 7, Episode 17: The Friendship Turbulence

After the insults fly, Bernadette tries to broker the peace between Howard and Sheldon by having the two travel together to Houston in an attempt to improve their friendship. Meanwhile, Penny is offered an embarrassing movie role and Raj asks Amy to write to a woman on his behalf.

  

Episode 153 - Season 7, Episode 18: The Mommy Observation

When Sheldon visits his mom (recurring guest star LAURIE METCALF) in Houston, he is forced to confront a new reality. Meanwhile, Raj’s “Murder Mystery” party starts some fights within the gang.

  

Episode 154 - Season 7, Episode 19: The Indecision Amalgamation

While Raj is wracked with guilt over dating two women at the same time and Penny is wrestling with whether to take a role in a cheesy movie, Amy must help Sheldon through the even greater hell of choosing between two gaming systems.

  

Episode 155 - Season 7, Episode 20: The Relationship Diremption

Sheldon faces a personal crisis after deciding he’s wasting his time with String Theory. Meanwhile, a double date between Raj, Emily and the Wolowitzes ends in embarrassment for Howard.

  

Episode 156 - Season 7, Episode 21: The Anything Can Happen Recurrence

Leonard tries to help Sheldon free his mind by reinstating “Anything Can Happen Thursday,” but when Sheldon tries to be spontaneous, it leads to unexpected friction between Penny, Amy and Bernadette. Meanwhile, Raj seeks Howard’s help in preparing for a date with Emily.

  

Episode 157 - Season 7, Episode 22: The Proton Transmogrification

May the “Fourth” Be With You! Professor Proton helps Sheldon cope with grief, while Leonard turns a relationship milestone into a competition with Penny. Meanwhile Amy and Bernadette make a “Star Wars Day gift for the guys.

  

Episode 158 - Season 7, Episode 23: The Gorilla Dissolution

A horrible day at work prompts Penny to evaluate her life choices – including taking a big step with Leonard. Meanwhile, Howard and Bernadette struggle to care for Mrs. Wolowitz, and Raj gets relationship advice from Sheldon.

  

Episode 159 - Season 7, Episode 24: The Status Quo Combustion

With his entire world changing around him, Sheldon is forced to confront an uncertain future and considers a major move in the seventh season finale. Meanwhile, Raj and Emily take it to the next level, and Mrs. Wolowitz’s injury is a major headache for Howard and Bernadette. Recurring guest star CHRISTINE BARANSKI returns as Leonard’s mother, Beverly Hofstadter.

  

Episode 160 - Season 8, Episode 1: The Locomotion Interruption

Leonard and Sheldon (series stars JOHNNY GALECKI and JIM PARSONS) are brilliant physicists – geniuses in the laboratory, but socially challenged everywhere else. Enter beautiful, street-smart neighbor, Penny (series star KALEY CUOCO-SWEETING), who aims to teach them a thing or two about life. Despite their on-again, off-again relationship in the past, Leonard and Penny have finally gotten engaged. Even Sheldon has found a female companion – entering into a “Relationship Agreement” with neurobiologist Amy Farrah Fowler (series star MAYIM BIALIK). In their free time, Leonard and Sheldon enjoy fantasy role-playing games with their ever-expanding universe of friends, including fellow scientists Raj (series star KUNAL NAYYAR) and Howard (series star SIMON HELBERG), and Howard's adorable microbiologist wife, Bernadette (series star MELISSA RAUCH).

  

Episode 161 - Season 8, Episode 2: The Junior Professor Solution

When Sheldon is forced to teach a class, Howard surprises everyone by taking it. Meanwhile, the tension between Penny and Bernadette gives Amy a chance to play both sides. Guest star REGINA KING returns as Mrs. Davis, the University’s Director of Employee Relations.

  

Episode 162 - Season 8, Episode 3: The First Pitch Insufficiency

Howard is nervous when NASA asks him to throw out the first pitch at a Los Angeles Angels game for National Space Day. Also, Leonard and Penny try to prove Sheldon wrong after he claims that he and Amy are a superior couple.

  

Episode 163 - Season 8, Episode 4: The Hook-Up Reverberation

Raj’s honesty about his past comes back to bite him after his girlfriend, is cold to Penny. Meanwhile, the guys consider becoming part-owners in Stuart’s comic-book store.

  

Episode 164 - Season 8, Episode 5: The Focus Attenuation

Amy and Bernadette accuse Penny of being a “buzzkill” after she gets an email from work during their Vegas weekend. Meanwhile, the guys try to invent something cool, but only come up with new ways to procrastinate.

  

Episode 165 - Season 8, Episode 6: The Expedition Approximation

Sheldon and Raj test whether they could survive a dark-matter research expedition in a salt mine by simulating the conditions in a steam tunnel deep underground. Meanwhile, Leonard and Penny seek advice from Wolowitz and Bernadette after they fight about money.

  

Episode 166 - Season 8, Episode 7: The Misinterpretation Agitation

The guys try to help Penny out of an awkward work dilemma, when a smitten doctor shows up at her door after her flirtatious sales techniques work a little too well. Meanwhile, Amy and Bernadette argue over whether or not female scientists should play up their sexuality.

  

Episode 167 - Season 8, Episode 8: The Prom Equivalency

When the gang recreates a high-school prom night on the roof of the guys’ apartment building, Sheldon feels pressure to participate in all the typical romantic traditions.

  

Episode 168 - Season 8, Episode 9: The Septum Deviation

When Leonard gets minor surgery on his nose, Sheldon is the one in need of sympathy. Meanwhile, Raj’s parents’ impending divorce causes Howard and Bernadette to work on their own marriage.

  

Episode 169 - Season 8, Episode 10: The Champagne Reflection

While Sheldon says a tearful goodbye to the final installment of “Fun with Flags,” Leonard, Howard and Raj search for something significant in a dead professor’s research. And Bernadette is shocked to learn of her co-workers’ true feelings from Penny.

  

Episode 170 - Season 8, Episode 11: The Clean Room Infiltration

Leonard and Howard turn to Raj for help in dealing with a work emergency when they nearly come to blows after blaming each other for a potential disaster at the university. Amy throws an authentic Victorian Christmas party, while Sheldon seeks revenge on her for making him celebrate the holidays

  

Episode 171 - Season 8, Episode 12: The Space Probe Disintegration

When the guys finally agree to do something the girls like, it leads to a confrontation between Leonard and Sheldon.

  

Episode 172 - Season 8, Episode 13: The Anxiety Optimization

In the hopes of achieving a scientific breakthrough, Sheldon invites his friends to challenge him and make him miserable. Meanwhile, Wolowitz invents an embarrassing game about Raj.

  

Episode 173 - Season 8, Episode 14: The Troll Manifestation

After Leonard and Sheldon co-publish a physics paper, they must defend themselves against criticism from an online bully. Also, girls’ night finds Penny, Amy and Bernadette confronting embarrassing moments from their pasts.

  

Episode 174 - Season 8, Episode 15: The Comic Book Store Regeneration

Howard receives some shocking news as everyone prepares for the reopening of Stuart’s comic book store. Penny teaches Sheldon how to “let it go” but can’t follow her own advice after she learns something infuriating about Amy. Also, Leonard and Raj think they spot Nathan Fillion at a restaurant.

  

Episode 175 - Season 8, Episode 16: The Intimacy Acceleration

When the gang hears about an experiment designed to make participants fall in love, Sheldon and Penny put it to the test as a joke. Meanwhile, Leonard, Amy, Raj and Emily spend the evening trying to escape a room with a “zombie.” And Bernadette and Howard run into trouble at the airport after returning from the funeral for Mrs. Wolowitz.

  

Episode 176 - Season 8, Episode 17: The Colonization Application

A trip to the pet store ends in a fight when Amy learns that Sheldon has applied for a one-way mission to colonize Mars. Also, Leonard surprises Penny with a very “adult” purchase; and Raj is caught snooping in Emily’s apartment.

  

Episode 177 - Season 8, Episode 18: The Leftover Thermalization

Friction ensues when a magazine fails to mention Leonard in an article about the paper he co-wrote with Sheldon. And a blackout at Mrs. Wolowitz’s home leads to a final family dinner in her honor.

  

Episode 178 - Season 8, Episode 19: The Skywalker Incursion

When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try to sneak on to George Lucas’s Skywalker Ranch to meet one of their idols. Back in Pasadena, Howard and Bernadette battle over the fate of his Dr. Who TARDIS, while Raj and Amy offer to settle the dispute with a game of ping pong.

  

Episode 179 - Season 8, Episode 20: The Fortification Implementation

When Sheldon and Amy build a blanket fort, they come to a big crossroads in their relationship. And Wolowitz is shocked when a man claiming to be his half-brother he never knew he had shows up at his front door. And, when Penny is invited to appear on Wil Wheaton’s podcast, she and Leonard have a huge, on-air argument

  

Episode 180 - Season 8, Episode 21: The Communication Deterioration

When Raj is asked to create a message in case a NASA mission discovers alien life, the guys fight over what he should do. Meanwhile, Penny is torn between auditioning for a movie or keeping her successful pharmaceutical sales job.

  

Episode 181 - Season 8, Episode 22: The Graduation Transmission

Wolowitz questions his engineering abilities when he and Sheldon can’t get a drone to fly. Meanwhile, a canceled flight nearly prevents Leonard from giving the commencement address at his former high school. And Raj pits his parents against each other when his father cuts him off financially.

  

Episode 182 - Season 8, Episode 23: The Maternal Combustion

Personalities collide and sparks fly when Sheldon and Leonard’s mothers (special guest stars LAURIE METCALF and CHRISTINE BARANSKI) finally meet. Meanwhile, Howard decides to “man up” and do his fair share of the housework – but not without a little help from his friends.

  

Episode 183 - Season 8, Episode 24: The Commitment Determination

In the eighth season finale, Sheldon presses Leonard and Penny to choose a date for their wedding, while dealing with dramatic changes in his own relationship with Amy.

  

Episode 184 - Season 9, Episode 1: The Matrimonial Momentum

In the ninth season premiere, Penny struggles with Leonard’s confession that he kissed another girl while on the North Sea. After driving to Vegas, Penny must now decide whether she wants to go through with the wedding. Back home, Sheldon doesn’t know how to act after Amy pushes pause on their relationship.

  

Episode 185 - Season 9, Episode 2: The Separation Oscillation

After Amy breaks up with Sheldon, he tries to retaliate by filming a special episode of “Fun with Flags.” Leonard, meanwhile, confronts the woman he kissed on the North Sea in an attempt to put Penny’s mind at ease, and Bernadette feels guilty about withholding a secret from Penny.

  

Episode 186 - Season 9, Episode 3: The Bachelor Party Corrosion

The guys’ science skills are put to the test when they get a flat tire during Leonard’s surprise bachelor party weekend in Mexico. Meanwhile, the girls force Penny to finally tell her family that she eloped with Leonard.

  

Episode 187 - Season 9, Episode 4: The 2003 Approximation

When Penny and Leonard announce they’re moving in together, Sheldon decides to revert back to 2003 – a simpler time before he met either of them. Meanwhile, Howard and Raj form a band to play at the Comic Book Store.

  

Episode 188 - Season 9, Episode 5: The Perspiration Implementation

When the guys take fencing lessons from Barry Kripke (recurring guest star JOHN ROSS BOWIE), Sheldon finds himself in an awkward position when Kripke expresses interest in Amy. Also, Stuart struggles to bring in female customers into the Comic Book Store, so Penny, Amy and Bernadette come by to help him out.

  

Episode 189 - Season 9, Episode 6: The Helium Insufficiency

In the midst of a nationwide helium shortage, Sheldon and Leonard take desperate measures to obtain the supplies they need on the black market. Meanwhile, Penny and Bernadette download a dating app on Amy’s phone in order to find her a new man. MICHAEL RAPAPORT guest stars as their Black Market dealer, Kenny.

  

Episode 190 - Season 9, Episode 7: The Spock Resonance

While being interviewed for a documentary about Spock, Sheldon struggles to suppress his emotions about his recent break-up with Amy – leaving Leonard and Penny shocked to discover that Sheldon had an engagement ring for Amy. Meanwhile, Howard and Bernadette disagree over remodeling his childhood home. Wil Wheaton, Adam Nimoy and Stephen Merchant guest star.

  

Episode 191 - Season 9, Episode 8: The Mystery Date Observation

With Amy out on a date with a mystery man, Sheldon enlists the help of Howard and Raj to find a new girlfriend by posting online. And when Amy is coy with the details about the guy she’s dating, Penny and Bernadette decide to spy.

  

Episode 192 - Season 9, Episode 9: The Platonic Permutation

Sheldon and Amy try hanging out as friends when they spend Thanksgiving together at the Aquarium. Meanwhile, Howard reluctantly agrees to volunteer at the soup kitchen with Bernadette, Raj and Emily, while Penny discovers that Leonard knows more about her than she thought.

  

Episode 193 - Season 9, Episode 10: The Earworm Reverberation

After driving Leonard and Penny crazy by his desperate attempts to remember the name of a song stuck in his head, Sheldon has a revelation when he realizes why. Then, despite their previously awkward date, Amy invites Dave (recurring guest star STEPHEN MERCHANT) over for dinner. And Howard and Raj become obsessed with a fan of their band, Footprints on the Moon.

  

Episode 194 - Season 9, Episode 11: The Opening Night Excitation

After more than five years of dating, Sheldon and Amy spend their first night together; while Leonard, Howard and Raj must decide who will take their extra Star Wars movie ticket. Recurring guest star BOB NEWHART returns as Sheldon’s Obi-Wan to advise him on his difficult relationship decisions.

  

Episode 195 - Season 9, Episode 12: The Sales Call Sublimination

Penny gets more than she bargained for when Leonard agrees to meet with a psychiatrist on her behalf. Sheldon and Raj collaborate on an astronomical discovery. Howard and Bernadette can’t believe what they’re feeling after Stuart moves out.

  

Episode 196 - Season 9, Episode 13: The Empathy Optimization

After having to deal with Sheldon being sick, Leonard, Penny and the gang try to treat themselves to a Sheldon free weekend.

  

Episode 197 - Season 9, Episode 14: The Meemaw Materialization

Sheldon’s thrilled when his Meemaw (guest star JUNE SQUIBB) comes to visit, but his excitement quickly fades when she butts heads with Amy. Also, Raj meets a new girl (guest star ALESSANDRA TORRESANI) at the comic book store who makes him question his relationship with Emily.

  

Episode 198 - Season 9, Episode 15: The Valentino Submergence

Sheldon and Amy host a special live Valentine's Day episode of "Fun with Flags." While Leonard and Penny grapple with getting older, Howard and Bernadette find a surprise in their hot tub; and Raj is torn between Emily and the cute girl he met at the Comic Book Store.

  

Episode 199 - Season 9, Episode 16: The Positive Negative Reaction

When the gang finds out about Bernadette’s pregnancy, they celebrate by singing karaoke. Meanwhile, Bernadette is concerned when Howard freaks out over her pregnancy announcement, as he’s convinced that he needs to make more money to provide for the baby.

  

Episode 200 - Season 9, Episode 17: The Celebration Experimentation

After more than nine years together, the gang finally celebrates Sheldon’s birthday with a few special guests on the 200th episode. CHRISTINE BARANSKI, SARA GILBERT and WIL WHEATON return and are joined by special guest star ADAM WEST.

  

Episode 201 - Season 9, Episode 18: The Application Deterioration

Leonard, Sheldon and Howard run into problems when they file for a patent for their infinite persistence gyroscope. Meanwhile, Penny, Amy and Bernadette give Raj dating advice after Emily reaches out to him after their breakup.

  

Episode 202 - Season 9, Episode 19: The Solder Excursion Diversion

When Sheldon’s laptop dies, it leads him to share a deep secret with Amy after she buys him a new one; Meanwhile, Raj sells out Leonard and Howard after they lie to their wives in order to attend an early screening of a movie.

  

Episode 203 - Season 9, Episode 20: The Big Bear Precipitation

Sheldon spills a secret of Leonard’s when the two take a weekend cabin trip with Penny and Amy; Meanwhile Howard and Bernadeitte must draw the line when Raj goes overboard with pregnancy gifts.

  

Episode 204 - Season 9, Episode 21: The Viewing Party Combustion

When a small argument between Leonard and Sheldon erupts into a heated fight, everyone must take sides during a group get-together.

  

Episode 205 - Season 9, Episode 22: The Fermentation Bifurcation

The gang goes to a wine bar and runs into Penny’s old boyfriend, Zack (recurring guest star BRIAN THOMAS SMITH); Bernadette gets stuck spending the evening with Sheldon when she can’t go wine tasting with the group, and things don’t go as planned when Raj introduces his new girlfriend, Claire (ALESSANDRA TORRESANI).

  

Episode 206 - Season 9, Episode 23: The Line Substitution Solution

Sheldon hires Stuart to spend the day with Amy when he’d rather go to a movie screening. Also, Leonard’s mother, Beverly, comes to town and Penny struggles to make a connection with her.

  

Episode 207 - Season 9, Episode 24: The Convergence Convergence

Chaos ensues in the ninth season finale when Leonard’s recently divorced parents (special guest stars JUDD HIRSCH and CHRISTINE BARANSKI) and Sheldon’s devoutly religious mother come to town. Meanwhile, Howard and Raj think the government is out to get them, when they’re contacted about their guidance system.

  

Episode 208 - Season 10, Episode 1: The Conjugal Conjecture

In the tenth season premiere, Penny’s family arrives for the wedding ceremony, including her anxiety-ridden mother, Susan (guest star KATEY SAGAL), her drug-dealing brother, Randall (guest star JACK McBRAYER) and her father Wyatt (returning guest star KEITH CARRADINE). After Sheldon’s mother, Mary (recurring guest star LAURIE METCALF) and Leonard’s father, Alfred (returning guest star JUDD HIRSCH) share an evening together, however, everyone deals with an awkward morning the next day. Recurring guest star CHRISTINE BARANSKI returns as Leonard’s mother, Dr. Beverly Hofstadter, while Breaking Bad’s DEAN NORRIS guest stars as Air Force Representative Colonel Williams.

  

Episode 209 - Season 10, Episode 2: The Military Miniaturization

Colonel Williams, an Air Force representative from the Department of Material Command, sits down for a talk with Howard.

  

Episode 210 - Season 10, Episode 3: The Dependence Transcendence

Tensions rise when the guys struggle to complete their government project on time – and Sheldon tries an energy drink to stay awake. Also, Penny and Amy go to a “party” at the house of Bert, the geologist (guest star BRIAN POSEHN). And Raj learns Bernadette’s true feelings about her pregnancy when they clean out the future baby room. Dean Norris returns as Air Force Colonel Williams.

  

Episode 211 - Season 10, Episode 4: The Cohabitation Experimentation

When Amy’s apartment floods, she proposes a “cohabitation experiment” with Sheldon. Meanwhile, Howard and Bernadette are upset when Raj learns the gender of their baby before they do.

  

Episode 212 - Season 10, Episode 5: The Hot Tub Contamination

Leonard and Penny must separate a quarreling Sheldon and Amy, when their cohabitation experiment doesn’t go as planned. Sheldon threatens to break off their relationship when Amy refuses to adhere to the “bathroom schedule.” Also, Howard and Bernadette find unexpected guests at their house when they decide to stay home from a planned vacation.

  

Episode 213 - Season 10, Episode 6: The Fetal Kick Catalyst

Penny is surprised to learn she has fans of her performance in “Serial Ape-ist” when she attends the Van Nuys Comic-Con with Leonard. Also, Amy hosts a Sheldon-style brunch at Penny’s apartment. And Howard makes an impulsive purchase when he starts stressing out about the baby on the way.

  

Episode 214 - Season 10, Episode 7: The Veracity Elasticity

In order to continue living with Sheldon, Amy lies to him about repairs being made to her apartment; and they host an “on location” episode of “Fun with Flags” in Penny’s apartment. Also, Leonard lets Penny decorate Sheldon’s old room after he learns that she has secretly been moving Leonard’s collectibles into storage.

  

Episode 215 - Season 10, Episode 8: The Brain Bowl Incubation

After a successful experiment combining their genes, Sheldon will stop at nothing to convince Amy they should procreate. Also, Raj is embarrassed to tell the gang what the new woman he’s dating does for a living.

  

Episode 216 - Season 10, Episode 9: The Geology Elevation

When CalTech geologist Bert (recurring guest star BRIAN POSEHN) wins the MacArthur Genius Fellowship, Sheldon is overcome with jealousy. Meanwhile, Howard finds an old remote control Stephen Hawking action figure he invented. STEPHEN HAWKING returns to guest star as himself.

  

Episode 217 - Season 10, Episode 10: The Property Division Collision

A battle ensues when Leonard and Sheldon argue over who will get custody of their shared belongings. Also, Raj and Stuart fight to be the most helpful during Bernadette’s final weeks of pregnancy. CHRISTOPHER LLOYD guest stars as Theodore.

  

Episode 218 - Season 10, Episode 11: The Birthday Synchronicity

While Sheldon and Amy celebrate Amy’s birthday, Howard and Bernadette welcome their new Baby Wolowitz.

  

Episode 219 - Season 10, Episode 12: The Holiday Summation

Sheldon and Amy visit Leonard and Penny for the first time since the holidays and share details about their terrible trip to Texas. Laurie Metcalf returns as Sheldon’s mother, Mary.

  

Episode 220 - Season 10, Episode 13: The Romance Recalibration

After Penny feels that Leonard is taking her for granted, she decides to go on a spa weekend with Amy, leaving Sheldon to play the unlikely peacemaker. Meanwhile, Howard and Raj try to fix a squeaky floorboard in the baby’s room.

  

Episode 221 - Season 10, Episode 14: The Emotion Detection Automation

Sheldon beta tests an MIT invention that helps him read people’s emotions. Meanwhile, Raj invites his ex-girlfriends over to give him dating advice, and Leonard can’t hide his feelings when Penny announces that her brother is coming to town. Guest stars LAURA SPENCER, KATE MICUCCI, ALESSANDRA TORRESANI and KATIE LeCLERC return as Raj’s ex-girlfriends.

  

Episode 222 - Season 10, Episode 15: The Locomotion Reverberation

Leonard and Howard try to distract Sheldon with tickets to a historic railway when he slows the progress of their guidance system. Meanwhile, Penny and Amy take Bernadette out for the night, leaving Raj and Stuart to care for baby Halley. Dean Norris returns as Colonel Williams.

  

Episode 223 - Season 10, Episode 16: The Allowance Evaporation

Sheldon and Amy have their first fight since moving in together, after he shares intimate details of their relationship with people at the university. Meanwhile, Raj is shocked by the realities of financial independence when he stops receiving support from his father (guest star BRIAN GEORGE).

  

Episode 224 - Season 10, Episode 17: The Comic-Con Conundrum

When Raj is cut off from his father’s fortune, he appoints Sheldon in charge of his finances to help him get out of debt. Also, Penny considers joining Leonard at Comic-Con.

  

Episode 225 - Season 10, Episode 18: The Escape Hatch Identification

When Raj moves out of his apartment, Leonard and Penny offer him Sheldon’s old room. Christine Baranski returns as Leonard’s mother, Beverly.

  

Episode 226 - Season 10, Episode 19: The Collaboration Fluctuation

Leonard, Penny and Raj adjust to their new living arrangement, while Sheldon takes an interest in Amy’s work.

  

Episode 227 - Season 10, Episode 20: The Recollection Dissipation

Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Howard as well as Amy on the same day. Also, Bernadette nears the end of her maternity leave and must return to work. JOEL MURRAY guest stars as Doug.

  

Episode 228 - Season 10, Episode 21: The Separation Agitation

Howard and Bernadette have a hard time leaving Halley in daycare when Bernadette returns to work. Also, Bert introduces the gang to his new girlfriend, Rebecca (guest star APRIL BOWLBY)

  

Episode 229 - Season 10, Episode 22: The Cognition Regeneration

Leonard isn’t thrilled when Penny considers taking a new job offered by her ex-boyfriend, Zack (guest star BRIAN THOMAS SMITH).

  

Episode 230 - Season 10, Episode 23: The Gyroscopic Collapse

After Leonard, Sheldon and Howard celebrate the completion of their top secret Air Force project, they’re met with an unpleasant surprise. Also, Amy is offered a summer position as a visiting researcher.

  

Episode 231 - Season 10, Episode 24: The Long Distance Dissonance

On the tenth season finale, the gang is concerned when Sheldon’s former admirer, Dr. Ramona Nowitzki (returning guest star RIKI LINDHOME) resurfaces while Amy is away at Princeton.

  

Episode 232 - Season 11, Episode 1: The Proposal Proposal

In the eleventh season premiere, Amy gives Sheldon an answer to his proposal, while Howard and Bernadette struggle with some unexpected news. LAURIE METCALF returns as Sheldon’s mother, Mary; RIKI LINDHOME returns as Ramona; and STEPHEN HAWKING returns as Himself.

  

Episode 233 - Season 11, Episode 2: The Retraction Reaction

Leonard angers the university – and the entire physics community – after he gives an embarrassing interview. Also, Amy and Bernadete bond over having to hide their success from Sheldon and Howard. NPR Host IRA FLATOW returns as himself, and REGINA KING returns as Mrs. Davis.

  

Episode 234 - Season 11, Episode 3: The Relaxation Integration

As Sheldon stresses out about picking a wedding date, Amy tries to convince him that he has a more laid-back side by recording him talking in his sleep. Meanwhile Raj and Stuart (series regular KEVIN SUSSMAN) compete to win the heart of Bernadette’s new coworker, Ruchi (guest star SWATI KAPILA).

  

Episode 235 - Season 11, Episode 4: The Explosion Implosion

Howard and Sheldon bond over their relationships with their disappointing fathers when they drive to the desert to shoot off a model rocket. Meanwhile, it rubs Leonard the wrong way when his mom (CHRISTINE BARANSKI) finds a new best friend in Penny.

  

Episode 236 - Season 11, Episode 5: The Collaboration Contamination

Raj and Sheldon confide in Bernadette when they can’t handle Amy working together with Howard. Meanwhile, Leonard and Penny learn new tactics for dealing with Sheldon from an unlikely source.

  

Episode 237 - Season 11, Episode 6: The Proton Regeneration

Sheldon goes head-to-head with WIL WHEATON (recurring as Himself) for the role of the new Professor Proton; Meanwhile, Penny steps in to take care of Halley when Bernadette and Howard both wind up on bed rest.

  

Episode 238 - Season 11, Episode 7: The Geology Methodology

Sheldon and Bert collaborate on a research project, despite Sheldon’s embarrassment. Meanwhile, Penny and Bernadette coach Raj on how to navigate his relationship with Ruchi.

  

Episode 239 - Season 11, Episode 8: The Tesla Recoil

Leonard and Howard are furious when they learn that Sheldon went to work with the military behind their backs. While Bernadette is on bed rest, she asks Raj go investigate when she suspects Ruchi might be trying to steal her job. Guest star DEAN NORRIS returns as Colonel Williams.

  

Episode 240 - Season 11, Episode 9: The Bitcoin Entanglement

Sheldon tries to teach the guys a lesson after they cut him out of a potentially valuable Bitcoin investment; A seven-year-old video reveals a secret about Leonard and Penny’s relationship.

  

Episode 241 - Season 11, Episode 10: The Confidence Erosion

Sheldon and Amy try to eliminate stress from wedding planning by applying math to the process. Also, Raj “breaks up” with Howard after realizing his best friend is actually hurting his confidence.

  

Episode 242 - Season 11, Episode 11: The Celebration Reverberation

Sheldon and Howard plan birthday celebrations for Amy and Halley, respectively. Leonard receives a Christmas letter from his brother that causes him to spiral out about his own lack of accomplishments.

  

Episode 243 - Season 11, Episode 12: The Matrimonial Metric

To discover who would be most qualified to be Best Man and Maid of Honor at their wedding, Sheldon and Amy subject their friends to a series of secret experiments; Penny reveals her true feelings about Amy.

  

Episode 244 - Season 11, Episode 13: The Solo Oscillation

When Sheldon kicks Amy out to work solo, she and Leonard bond during a series of science experiments. Meanwhile, Bert, the geologist, replaces Howard in his band, “Footprints on the Moon,” and Sheldon finds Penny a surprising source of scientific inspiration.

  

Episode 245 - Season 11, Episode 14: The Separation Triangulation

Raj finds himself in the middle of a domestic drama when he learns the woman he’s dating, Nell (guest star BETH BEHRS), has a very upset husband, Oliver (guest star WALTON GOGGINS). Also, when Sheldon rents his old room back for a quiet place to work, he drives Leonard crazy by being a model tenant.

  

Episode 246 - Season 11, Episode 15: The Novelization Correlation

When Sheldon petitions Wil Wheaton to appear on the new Professor Proton show, Wil offers a role to Amy instead; Penny gets angry when she thinks the female protagonist in Leonard’s novel is based on her.

  

Episode 247 - Season 11, Episode 16: The Neonatal Nomenclature

When Bernadette won’t go into labor, all her friends try different tactics to get things started; and Howard confronts Bernadette after Amy accidentally reveals that she’s already chosen their son’s name.

  

Episode 248 - Season 11, Episode 17: The Athenaeum Allocation

While Leonard jumps through hoops to help secure the perfect wedding venue for Sheldon and Amy, Howard and Bernadette have a difficult time deciding which one of them should stay at home with the kids and who should return to work.

  

Episode 249 - Season 11, Episode 18: The Gates Excitation

When Penny gets the opportunity to host BILL GATES (guest starring as himself) at work when his company wants to partner with her pharmaceutical company, Leonard, Howard and Raj do everything in their power to meet him, while Sheldon thinks he’s the victim of an April Fool’s prank.

  

Episode 250 - Season 11, Episode 19: The Tenant Disassociation

When Leonard learns Sheldon is the president of the Tenants Association, he decides to run against him; Bernadette encourages Howard and Raj to find the owner of a drone after they find it in the backyard.

  

Episode 251 - Season 11, Episode 20: The Reclusive Potential

A brilliant, but reclusive scientist, Doctor Wolcott (guest star PETER MacNICOL) invites Sheldon to his cabin in the middle of nowhere, and Leonard, Howard and Raj go along for the trip. Penny and Bernadette improvise when Amy doesn’t like the tame bachelorette party they planned for her.

  

Episode 252 - Season 11, Episode 21: The Comet Polarization

Sheldon’s comic book store experience changes when writer NEIL GAIMAN (Coraline, American Gods) puts Stuart’s store on the map. And friendships are threatened when Raj takes credit for Penny’s astronomical discovery.

  

Episode 253 - Season 11, Episode 22: The Monetary Insufficiency

Sheldon goes to Vegas and does everything he can to win three hundred million dollars for science. Meanwhile, Penny and Bernadette take Amy shopping for wedding dresses, but her terribly choice entangles them in a web of lies.

  

Episode 254 - Season 11, Episode 23: The Sibling Realignment

When Sheldon learns that his mother won’t attend his wedding unless he invites his older brother, Georgie, he and Leonard travel to Texas to end a family feud. Meanwhile, the Wolowitz kids inadvertently infest Amy, Bernadette, Howard and Raj with pinkeye.

  

Episode 255 - Season 11, Episode 24: The Bow Tie Asymmetry

On the eleventh season finale, Amy’s parents (guest stars KATHY BATES and TELLER) arrive along with Sheldon’s family (guest stars LAURIE METCALF, JERRY O’CONNELL and COURTNEY HENGGELER). And everybody’s focused on making sure all goes according to plan – everyone except the bride and groom. MARK HAMILL and WIL WHEATON also guest star.

  

Episode 256 - Season 12, Episode 1: The Conjugal Configuration

In the twelfth season premiere, Sheldon and Amy’s honeymoon runs aground in New York, while Penny and Leonard discover they are uncomfortably similar to Amy’s parents; Meanwhile Raj insults physicist NEIL DEGRASSE TYSON and starts a Twitter war. KATHY BATES and TELLER return as Amy’s parents.

  

Episode 257 - Season 12, Episode 2: The Wedding Gift Wormhole

Sheldon and Amy drive themselves crazy trying to figure out what “perfect gift” Leonard and Penny got them for their wedding. Meanwhile, Raj decides he wants to settle down and asks his father to find him an arranged marriage.

  

Episode 258 - Season 12, Episode 3: The Procreation Calculation

Howard and Bernadette’s life gets complicated when Stuart (series regular KEVIN SUSSMAN) starts bringing his new girlfriend home. Meanwhile, Penny and Leonard talk about starting a new family, as Raj explores an arranged marriage.

  

Episode 259 - Season 12, Episode 4: The Tam Turbulence

When Sheldon won’t tell anyone why he’s never mentioned Tam (guest star ROBERT WU), his childhood best friend, Leonard takes matters into his own hands. Also, Bernadette and Penny take out Raj’s fiancée, Anu (guest star RATI GUPTA), for dinner to get all the details on her. JERRY O’CONNELL returns as Sheldon’s brother, George.

  

Episode 260 - Season 12, Episode 5: The Planetarium Collision

When Amy doesn’t have time to work on super-asymmetry, Sheldon goes to great lengths to ensure she’s available to work with him even if it means accidentally sabotaging her career in the process. Meanwhile, Raj doesn’t want Howard to join him in hosting a show at the planetarium. BOB NEWHART returns as Arthur Jeffries.

  

Episode 261 - Season 12, Episode 6: The Imitation Perturbation

When Howard dresses up as Sheldon for Halloween, Sheldon seeks retaliation at Leonard and Penny’s Halloween party; Meanwhile, Leonard is shocked that Penny doesn't remember their first kiss.

  

Episode 262 - Season 12, Episode 7: The Grant Allocation Derivation

Leonard is caught between a rock and a hard place when he’s responsible for distributing extra grant money. Also, Bernadette turns the backyard playhouse into a hideaway from her husband and kids.

  

Episode 263 - Season 12, Episode 8: The Consummation Deviation

Sheldon tries to bond with Amy’s father. But when Howard lures Mr. Fowler away with magic tricks, Sheldon has no choice but to bond with Mrs. Fowler. Meanwhile, Raj and Anu attempt to get physical.

  

Episode 264 - Season 12, Episode 9: The Citation Negation

Sheldon and Amy are devastated to learn from a Russian paper that Super-Asymmetry has already been discovered and disproven. Meanwhile, ultra-competitive Bernadette asks Stuart’s girlfriend, Denise (recurring guest star LAUREN LAPKUS), to teach her how to play the videogame Fortnite.

  

Episode 265 - Season 12, Episode 10: The Vcr Illumination

Sheldon and Amy are still down about their theory being disproven, but a VHS tape from Sheldon’s past inspires him to not give up. Also, Bernadette turns into a pageant mom when she tries to help Howard ace his Magic Castle audition. Special guest stars include Young Sheldon’s IAIN ARMITAGE, LANCE BARBER and MONTANA JORDAN. CHRISTINE BARANSKI returns as Leonard’s mother, Beverly.

  

Episode 266 - Season 12, Episode 11: The Paintball Scattering

Penny and Leonard organize a paintball game that results in mayhem, when Sheldon is jealous of Amy, Raj catches Anu with her ex-boyfriend, and Stuart doesn’t want to move in with Denise.

  

Episode 267 - Season 12, Episode 12: The Propagation Proposition

Penny’s old boyfriend, Zack (recurring guest star BRIAN THOMAS SMITH), and his wife want a baby, but when Zack is infertile, they ask Leonard to help. Meanwhile, Raj attempts to mend things with his ex-fiancée Anu.

  

Episode 268 - Season 12, Episode 13: The Confirmation Polarization

When Sheldon and Amy’s Super Asymmetry Theory is proven by two physicists from Chicago, they’re thrilled – until they try to kick Amy off their Nobel Prize nomination! Meanwhile, Bernadette has a big success at work and Penny’s going to be a part of it…whether she wants to or not.

  

Episode 269 - Season 12, Episode 14: The Meteorite Manifestation

Sheldon is thrilled to help Howard and Bernadette navigate bureaucratic paperwork… until he discovers they are breaking the law. Now, he’ll have to choose between following the rules of staying loyal to his friends. Meanwhile, Leonard is disappointed when his friends exclude him from a scientific project.

  

Episode 270 - Season 12, Episode 15: The Donation Oscillation

Penny tries to seduce an abstaining Leonard to ruin his “donation” for her ex-boyfriend, Zack, and his wife, Marissa (recurring guest star LINDSEY KRAFT). Meanwhile, Howard, Bernadette, Raj and Anu turn Raj’s canceled bachelor party into a “couple’s trip” aboard the “Vomit Comet.” Keith Carradine returns as Penny’s father, Wyatt.

  

Episode 271 - Season 12, Episode 16: The D & D Vortex

When the gang finds out that Wil Wheaton hosts a celebrity Dungeons & Dragons game involving WILLIAM SHATNER, JOE MANGANIELLO, NBA legend KAREEM ABDUL-JABBAR and director KEVIN SMITH, deception and betrayal are the path to make it to the one open seat.

  

Episode 272 - Season 12, Episode 17: The Conference Valuation

When Penny and Bernadette got to San Diego for a pharmaceutical sales convention, Howard is left in charge of the kids. But when Sheldon finds a book on experimenting with children, the guys and Amy make a day of it.

  

Episode 273 - Season 12, Episode 18: The Laureate Accumulation

When competitors Pemberton and Campbell (guest stars SEAN ASTIN and KAL PENN) charm America on a publicity tour, Sheldon and Amy try to bring Nobel laureates KIP THORNE, GEORGE SMOOT and FRANCES ARNOLD to their side (this episode sets the record for most Nobel laureates appearing in a comedy). Meanwhile, Halley’s fear of the dark leads to both opportunity and conflict for Howard, Bernadette and Stuart.

  

Episode 274 - Season 12, Episode 19: The Inspiration Deprivation

The concept of what it would mean for women everywhere if Amy were to win a Nobel Prize causes Amy to have a meltdown. Meanwhile, Raj and Howard try to relive the good old days when Howard buys a scooter that resembles the one he had years ago.

  

Episode 275 - Season 12, Episode 20: The Decision Reverberation

While Raj is worried that people won’t take him seriously in his own field after publishing a paper suggesting he may have discovered alien life, Penny encourages Leonard to stand up for himself when he wants to be the principal investigator on a plasma physics study.

  

Episode 276 - Season 12, Episode 21: The Plagiarism Schism

When Barry Kripke finds proof that Dr. Pemberton plagiarized his thesis in college, Sheldon and Amy aren’t sure if they should turn him in or not. And Howard is happily surprised to learn that Bernadette wasn’t the only waitress at The Cheesecake Factory who had a crush on him back in the day.

  

Episode 277 - Season 12, Episode 22: The Maternal Conclusion

Leonard is pleasantly surprised when his mother, Beverly, comes to visit and she’s genuinely kind toward him – until he finds out the real reason why she’s there; Meanwhile, Denise and Stuart overstay their welcome at the Wolowitz house.

  

Episode 278 - Season 12, Episode 23: The Change Constant

This week an all new episode of The Big Bang Theory.

  

Episode 279 - Season 12, Episode 24: The Stockholm Syndrome

It’s an end and a beginning on the second of a two-part series finale. Howard and Bernadette leave their kids for the first time; Leonard and Penny try to keep a secret; Sheldon and Amy stick together; and Raj makes a new friend as the gang travels together into an uncharted future.

  



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