Unaired Pilot

1 :01x01 - Pilot

Leonard and Sheldon visit a high IQ sperm bank, but have regrets about going, so they leave, only to feel guilty afterwards. When they arrive back at the apartment, they see a beautiful blond woman, Penny, in the apartment across the hallway and they attempt to befriend her. Sheldon, who has no experience being around someone like Penny, doesn’t know what to do, while Leonard really takes a shine to her. Meanwhile, Howard makes numerous attempts to impress Penny, while Koothrappali is too shy to talk to her.

2 :01x02 - The Big Bran Hypothesis

A Superman movie marathon is disrupted when Penny asks the guys to sign for a package that may be delivered while she’s gone. But when the guys discover that the package is huge, they understand it’s going to take some hard work to get it up all the stairs. When they finally do so and manage to get into Penny’s apartment with the spare key she gave Leonard, Sheldon is shocked about how messy her apartment is, and decides to clean it during the night while Penny is sleeping. However, when Penny wakes up, she is furious that they were in her apartment and Leonard is sad while she is angry at them.

3 :01x03 - The Fuzzy Boots Corollary

The guys are playing a computer game, but are interrupted when they hear Penny laughing across the hall. But Leonard is in for a shocking discovery when he sees hear kissing with another guy. Trying to recover from the shock, Howard advices Leonard to date Leslie Winkle, one of the co-workers at the lab. Leonard agrees to do so, but things only get worse for him when Leslie turns him down. However, after Sheldon somehow manages to build up Leonard's self-confidence, Leonard tricks Penny into going on a date with him, but Leonard has a panic attack right before the date and it might ruin what was supposed to be a nice, romantic evening.

4 :01x04 - The Luminous Fish Effect

When Sheldon gets fired, he tries to explore life like everyone else sees it. He goes food shopping with Penny, although she is less than happy about it, and afterwards he starts to perform a lot of different experiments he hasn’t been able to do with his busy job. It gets so serious that Leonard calls Sheldon’s mom for advice and she decides to make a visit to Sheldon, who becomes angry about Leonard calling her without his permission.

5 :01x05 - The Hamburger Postulate

Playing with salt and pepper shakers at the Cheesecake Factory, the guys are forced to order or leave, and they decide to order. But Sheldon hasn’t eaten at the Factory before and therefore doesn’t know what’s good. Ending the argument, Leslie Winkle sees Leonard and asks if he wants to play the cello in a musical ensemble, an offer that Leonard agrees to, and the first practice is at his apartment. The practice doesn't turn out exactly as planned, however, when it turns into a sexual encounter. Sheldon, who has no experience being in the situation of knowing someone is just a few feet away making love, seeks wisdom from Penny.

6 :01x06 - The Middle Earth Paradigm

Embarrassed after being defeated by a Bar Mitzvah party at paintball, the guys are surprised when Penny invites them to her upcoming Halloween & Costume party. They decide to go, but for them, the party is a disaster. Sheldon, who is sad that there is not going to be a costume parade and awards, tries to make people guess what he has dressed up like, while Howard tries to impress different women at the party but with no success. Leonard gets in a disturbing situation when Penny’s ex-boyfriend Kurt shows up at the party and insults him, and Koothrappali tries not to talk to any women because of his mythology, but a situation pops up that result in him and a girl in bed together.

7 :01x07 - The Dumpling Paradox

Penny asks the guys if she can spend the night in their apartment when a friend of her from Omaha is visiting. Apparently, her friend is a very bad person and Penny dislikes her, although Howard seems to really like her. Trying to make time pass while Howard is in her apartment with her friend, Penny joins Leonard, Sheldon and Koothrappali playing Halo, but Sheldon gets angry when she is much better than he is at the game.

8 :01x08 - The Grasshopper Experiment

Koothrappali is not happy when his parents inform him that they have set up a blind date with a girl he knew from his childhood years. Apparently, the girl bullied Koothrappali a lot. His friends try to cheer him up, but there is no way out of it. Meanwhile, Penny has gotten a job that includes mixing drinks and she wants to practice mixing for the guys. However, everyone make a shocking discovery when Koothrappali has a drink, and manages to talk to the opposite sex.

9 :01x09 - The Cooper-Hofstadter Polarization

The guys are performing a new scientific experiment, that includes sending a message around the world from their computer and, without using the remote, control any electricity in the room they’re in. While cleaning up afterwards, Leonard discovers a note from a science company wanting him and Sheldon to present one of their experiments. However, Sheldon does not want to present the case, while Leonard is quite happy and decides to do it, with Sheldon forbidding him to do so.

10 :01x10 - The Loobenfeld Decay

In the middle of a discussion, Leonard and Sheldon hear Penny’s awful singing, and when they see her coming down the stairs, they try to escape unsuccessfully. Penny informs them that she has gotten a singing role in a small play, but the big thing about it is that a lot of talent scouts are going to be there, and she is hoping for a real chance in show business. Because they don’t want to be there, Leonard cooks up a lie in which him and Sheldon are going to a symposium, but Sheldon feels guilty about the lie afterwards and cooks up a new plan that involves a fake cousin.

11 :01x11 - The Pancake Batter Anomaly

Leonard and Sheldon are playing 3D Chess, but Leonard loses once again. Luckily for him, the conversation is disrupted when Penny comes home from her visit in Nebraska, but Sheldon is shocked when she tells them that her family got sick over the weekend. The result is that Sheldon gets paranoid about not getting sick, but when he does, it gets so bad he forces Penny to take care of him while the guys are out trying to avoid coming home.

12 :01x12 - The Jerusalem Duality

While having lunch at the lab’s cafeteria, Leonard and Sheldon are introduced to a 15-year-old boy prodigy who happens to be equally as smart as or even smarter than Sheldon, which has him angrier than ever. Knowing everything he will do in the future will somehow be corrected by the boy, Sheldon stops working at the lab and instead tries to help his fellow friends with their experiments, but they are less than happy about it. Finding out that Sheldon really needs to become the best achiever again, the guys cook up a plan to make the boy lose his focus.

13 :01x13 - The Bat Jar Conjecture

Howard receives a mail on his cell phone saying that there is an open spot for a team at a Physics Bowl event coming up and the guys grab the opportunity. But when it turns out Sheldon answers all the questions during the rehearsals, the guys decide that he is off the team, but to fill in the remaining spot on the Bowl, Leslie Winkle agrees to be on their team. However, planning to make sure the guys don’t outsmart him, Sheldon creates his own team to join, even though he will be the one answering the questions.

14 :01x14 - The Nerdvana Annihilation

Leonard is bidding in an auction for a miniature time machine, but wasn’t expecting to actually get it. When he does so and it is delivered, the guys are shocked to learn that it isn’t a miniature after all and end up injuring themselves while carrying it up the stairs. Afterwards, Penny is even more shocked that they even bother to use so much time on stuff like that, so she calls them “pathetic”, hurting Leonard’s feelings terribly and resulting in him getting rid of all his geek stuff.

15 :01x15 - The Pork Chop Indeterminacy

Sheldon gets a visit from his twin sister, Missy, who seems to be a much more interesting person that Sheldon believes she is. Leonard, Howard and Rajesh all seem to have a crush on her and everyone seems willing to fight for her love. This results in Sheldon deciding to pick out who she will go out with (despite her disapproval), but when the guys finally have enough strength to actually ask her out, they find out she is only interested in one person.

16 :01x16 - The Peanut Reaction

Finding out that Leonard has never had a birthday party thrown for him, Penny convinces the guys to create a surprise party. Howard and Raj are in on the idea, while Sheldon envies Leonard for never having the experience (due to bad childhood memories). However, when Penny finally convinces him and they go to the store to buy presents, Sheldon finds out that the customers in the store needs his help much more than Leonard, making the plan fall out of schedule.

17 :01x17 - The Tangerine Factor

When Penny breaks up with her boyfriend after she finds out he has been posting about their sex life on his blog, Leonard gets enough courage to ask her out on a real date. Penny is so depressed about the recent break-up, she agrees to go out with Leonard, but when they both face the reality of going out afterwards, they stress out so they much they both seek information about one another from Sheldon, a rather reluctant advisor.

18 :02x01 - The Bad Fish Paradigm

Leonard and Penny return from their date, but it ends in an odd matter when Penny wants to take things slower. While Leonard is living his normal everyday life, Penny is now worrying if she is smart enough for Leonard, as she has none of the same interests as him, so she seeks advice from Sheldon and even tells him a secret. However, when it turns out Sheldon can’t keep her secret, the relationship between Leonard and Penny may be broken forever.

19 :02x02 - The Codpiece Topology

After Leonard sees Penny with a new guy, he decides it’s time to move on with his life. When Leslie Winkle enters the lab, she invites Leonard to get a relationship. However, Sheldon hates Leslie and Penny wants them to break up, so Penny receives advice from Sheldon, but with no good results. Meanwhile, the relationship hits a bump when it turns out Leonard rather supports Sheldon’s science theories than Leslie’s.

20 :02x03 - The Barbarian Sublimation

When Penny becomes depressed due to the thoughts that she fails everything in life, the guys try everything to make her better, but with no results. However, when Penny sees Sheldon’s game, “Age of Conan”, she becomes addicted playing it, and winds up a slob. Meanwhile, the evil sparks between Sheldon and Leslie have still not disappeared.

21 :02x04 - The Griffin Equivalency

When Koothrappali discovers a new planet, he is honored the ”30 under 30” award from People Magazine, and the guys try to show their spirit by inviting him to dinner, but there is one person who just can’t show his support; Sheldon, who believes receiving an award for something that the recipient didn’t actually create, is fake. The guys try to convince him into thinking otherwise, but when Koothrappali’s self-esteem builds up to the max, he becomes so obnoxious that they all try to avoid him. Meanwhile, Koothrappali invites Penny to go the People Magazine party, but the only way he can talk to Penny is while being drunk, which puts a halt to their friendship.

22 :02x05 - The Euclid Alternative

When Leonard does experiments where he needs to use a laser only available during the night, he is unable to drive Sheldon to and from work in the morning. Sheldon, who can’t drive, seeks help from Penny, Howard and Koothrappali, but they all get so angry they refuse to drive him. However, the only way for them to get Sheldon off their back is to get him driving a car, which he’s terrible at, leaving the guys and Penny between a rock and a hard place.

23 :02x06 - The Cooper-Nowitzki Theorem

After speaking at a student seminar, Sheldon quickly finds himself in an unusual situation; a girl approaches him interested in helping him with his research. Not needing the help, Sheldon instead gets her to take care of all his daily work for him so he can focus entirely on his work. However, when she gets too pushy, going as far as washing his feet while he works, Sheldon seeks advice from Penny in order to get her off his back, but it’s harder than they thought. Meanwhile, the guys are baffled that someone can survive a full day with Sheldon as she does, and they begin to miss Sheldon during Halo, paintball and other such activities.

24 :02x07 - The Panty Piñata Polarization

Officially becoming a member of their group, according to Sheldon, Penny has huge problems fitting in with the house rules. When Penny gets “3 strikes”, she is banished and can’t even talk to Sheldon anymore, putting Leonard in a difficult situation where he must choose which side of the argument he should stay on. Meanwhile, Penny declares a war between Sheldon and her, where the weak sides of them both are exposed; Penny’s lingerie is put out on a telephone wire, while Sheldon’s “laundry day” is ruined when all the machines are taken, and there seems to be no end of this war.

25 :02x08 - The Lizard-Spock Expansion

Wolowitz has once again used his “dating skills” to make a mess when he invites a girl, Stephanie, to drive the Mars Rover, only to have it stuck in a ditch. He now needs help from the other guys, but he also wants someone to take care of Stephanie, whom Leonard drives home. However, when Leonard and Stephanie kiss in the car and start a relationship, Wolowitz becomes so angry at him he starts ignoring them both completely. Meanwhile, Penny is so happy that Leonard is in a relationship, but he’s not sure if it pushes Penny away from him or not.

26 :02x09 - The White Asparagus Triangulation

The relationship between Leonard and Stephanie is going quite well, but Sheldon really likes her and is afraid Leonard isn’t manly enough. Therefore, he decides to create a situation where he needs help from Leonard in order to make him look big in front of Stephanie. However, when his plan backfires, Sheldon becomes so worried that their relationship might end that he goes as far as hacking Leonard’s computer.

27 :02x10 - The Vartabedian Conundrum

When Penny uncovers the truth in Leonard and Stephanie’s relationship, that they are only dating because she likes him, Penny decides to council Leonard on the subject. She tells him that his feelings are just as important as everybody else’s, and this gives Leonard the courage to break up with Stephanie… he thinks. After failing to break up several times, he doesn’t know whether to stay in an unsuccessful relationship, or break up and stay single until he can find someone else.

28 :02x11 - The Bath Item Gift Hypothesis

When Leonard meets David Underhill, an award-winning scientist who is the exact opposite of Leonard (handsome, cool and intelligent), Leonard is put in the worst situation he can imagine when David and Penny become more than friends. Meanwhile, Penny buys a Christmas gift for Sheldon, but unfortunately, Sheldon thinks of Christmas as an annoying part of the year where the recipient of a gift is tied to a promise to give the sender a gift back, and Sheldon doesn’t know what to do.

29 :02x12 - The Killer Robot Instability

After Kripke challenges them to a robot duel, the guys build MONTE; a killer robot with many deadly features. But when their robot loses the competition, the guys are humiliated in front of Kripke. Meanwhile, Penny finally tells Howard about his rude behavior towards women, which actually has really, really bad effects on him when he goes into a depression, memorizing all his girlfriend troubles and wondering why he can’t pick up girls.

30 :02x13 - The Friendship Algorithm

When Sheldon finds out that Kripke is the only person who controls a new supercomputer at the University, Sheldon makes it his mission to befriend Kripke, but due to his problems making friends, Sheldon takes a scientific procedure, which works. However, their friendship may disappear again when it is uncovered that Kripke actually does not have any control of the supercomputer.

31 :02x14 - The Financial Permeability

After Penny enters a financial crisis, Sheldon lends her money, which she is uncomfortable about. Leonard decides to figure out what the cause of the crisis is, and soon finds out that Penny’s ex-boyfriend Kurt owes her money that he still hasn’t returned. Leonard confronts Kurt with the rest of the guys as back-up, but the plan hits a halt when Kurt gives the money back, but also continues his relationship with Penny.

32 :02x15 - The Maternal Capacitance

When Leonard’s mother, Beverly, comes for a visit, a normal week for the guys and Penny takes a much unexpected turn; Beverly is a neuroscientist who talks to Penny about her problems (making Penny cry like a little girl), Leonard becomes so tired he spends much time in Penny’s apartment (in Penny’s bed… with Penny), Sheldon finds an unusually comfortable person in Beverly, and she believes Rajesh and Howard are in a homosexual sex-relationship.

33 :02x16 - The Cushion Saturation

Penny finds herself in the worst situation ever when she accidentally shoots a paintball pellet on Sheldon’s cushion, also known as his “spot” on the couch. While she desperately tries everything to fix it, Sheldon is now left with no option rather than to always stand or find another place to sit; much to his dismay. Meanwhile, Leslie and Howard start a sexual relationship together, but he doesn’t know there are no feelings in it, and he asks himself whether or not he likes the idea of being used as a sex object. However, when it turns out Leslie has access to extra grant money which she is willing to give to him so he can continue his research; he becomes really unsure what to do.

34 :02x17 - The Terminator Decoupling

Aboard a train on their way to San Francisco for a symposium held by Dr. George Smoot, each of the guys has their own separate problems on the train. While Sheldon is desperately finding a way to retrieve his paper he forgot at home, Leonard tries to get some sleep, but it’s difficult with Sheldon’s constant nagging. Meanwhile, Koothrappali and Howard attempt to hit on an actress they spot on the train (Summer Glau, “The Terminator”), but they fight about who should get her and they both destroy one another’s chances at love.

35 :02x18 - The Work Song Nanocluster

Penny wants to start her own business, making hair clips she calls ”Penny Blossoms”, but she has no marketing, manufacturing or commercial knowledge, and receives help from the guys, especially Sheldon. However, when they get an over-night order with 1000 Penny Blossoms, it’s going to take a lot more than “hard work” to complete the order within the 24 hours they have. Meanwhile, Penny convinces Sheldon into drinking his first cup of coffee, but the results are Sheldon becoming hyperactive and acting as if he was using drugs.

36 :02x19 - The Dead Hooker Juxtaposition

Penny feels threatened when a new, very hot girl moves into the apartment right above the guy’s and start using her looks to get help from the guys; fixing stereos and driving her places. Penny, going crazy that she can’t even talk to the guys anymore as they don’t listen to her, understands she has to do something with this new girl, and confronts her. However, the confrontation is a little bit more than just a swear word or two and ends in a chick fight.

37 :02x20 - The Hofstadter Isotope

When Stuart, the sales clerk at the comic book store, charms Penny completely and gets her to go out with him, everyone is baffled at how he did it. Leonard’s dismay that Penny would go out with Stuart and not him drives him insane, but when an argument between Sheldon and Stuart results in a break-up between Stuart and Penny, Leonard offers his shoulder for Penny “to cry on”. Meanwhile, Howard and Koothrappali head to a women’s bar to pick up girls, and while Howard fails at getting sex, Koothrappali scores… surprisingly.

38 :02x21 - The Vegas Renormalization

When Leslie breaks up with Howard, he becomes so devastated he agrees to go with Leonard and Koothrappali to Las Vegas to cheer him up. But when they arrive, it turns out being a difficult job in itself to get Howard outside the apartment, as all he does is tracking Leslie’s online activities. Meanwhile, Sheldon locks himself out of the apartment back home and much to his and Penny’s dislike spends the night in Penny’s apartment, but he is not able to perform his daily routines and misses home.

39 :02x22 - The Classified Materials Turbulence

Another date between Penny and Stuart (the sales clerk at the comic book store) ends in disaster when Penny calls out Leonard’s name instead of Stuart’s during a make-out. When Leonard finds out, he doesn’t know exactly what to do, but given the thought that he on purpose gave Stuart bad advices on how to proceed on the date with Penny, he gets a bad conscience. Meanwhile, Howard discovers a big design flaw in his NASA Space Toilet, and needs emergency help from his friends, but it may not be enough.

40 :02x23 - The Monopolar Expedition

When Sheldon meets with the University’s Dean, who requests that he leads an arctic expedition to the North Pole, Sheldon asks the guys if they would like to come along. After much consideration, the guys decide to go with him, but they regret it every second during the harsh and cruel training for the extremely cold weather they can be expecting at the North Pole. Meanwhile, Penny hears the news that they’re going away, and decides to show Leonard that she cares about him by knitting him a scarf. However, he believes there may be secret feelings in the scarf, in which she doesn’t want him to go even though she says she will just miss him.

41 :03x01 - The Electric Can Opener Fluctuation

The guys are coming home from the North Pole, but only Sheldon is satisfied with the trip, while the rest don’t have very good opinions. Inside their room, Sheldon is shocked to learn that the guys tampered with his data from the experiments he performed, and when nobody seems to understand how sad or furious he is, he leaves to Texas in disgrace. Meanwhile, Penny is more than happy to see that Leonard has come home, and their relationship goes to a whole new level when Penny kisses him incessantly.

42 :03x02 - The Jiminy Conjecture

It’s comic-book-night for the guys, but they are surprised to see Leonard there. Howard and Raj were expecting him to be having sex with Penny, but as Leonard reveals only to get them off his back, the previous night they spent together was “just fine”. When Sheldon brings this up during a normal conversation, it shocks Penny what Leonard actually tells the guys. Meanwhile, when Howard and Sheldon hear a cricket in the apartment, they start arguing about what species the cricket belongs to, and end up betting their best comic books against each other.

43 :03x03 - The Gothowitz Deviation

Sheldon is getting sick of Penny’s misbehavior, and decides to do something about it. He uncovers that Penny has a “thing” for chocolate, and decides to use it in order for her to get a better mood and behavior towards him. Meanwhile, Raj and Howard want to pick up women, and their newest attempt has them dressed like Goths and going to a Goth nightclub, where they try to impress the women, but it doesn’t go flawless.

44 :03x04 - The Pirate Solution

It’s a typical day for the boys until Raj runs out of the apartment crying. Howard decides to talk to him and when he comes back, he brings the worst news ever: Raj is getting deported. The only way he can avoid deportation is to get a new job, and he goes as far as agreeing to work for Sheldon in order to remain in the country. Meanwhile, Leonard and Penny try to get some time for themselves, but have to deal with Howard as a third wheel.

45 :03x05 - The Creepy Candy Coating Corollary

Penny loses in a card game, but is surprised when it turns out Sheldon has a special gift in those sorts of games; he can calculate what the opponent’s cards are just from his mind. Afterwards at the comic book store, Sheldon is positively shocked to learn that Wil Wheaton is entering the same card game that Koothrappali is in, and he agrees to be Raj’s partner. Meanwhile, Howard persuades Penny into hooking him up with one of her friends.

46 :03x06 - The Cornhusker Vortex

The guys are going outside to play with kites, but Leonard meets with Penny down the stairs and feels jealous when Penny tells him that she is going to have a friend over and watch football (something Leonard doesn’t understand). However, Leonard discusses the matter with Penny and end up needing to learn the rules of football, but his only choice for help is Sheldon. Meanwhile, during a kite competition between Howard and Raj, Howard leaves to chase a girl, leaving Raj angry at him.

47 :03x07 - The Guitarist Amplification

Leonard, Penny and Sheldon are playing a game that Sheldon created himself, but there’s more than just the game going on when Leonard and Penny start arguing loudly about Leonard being jealous than Penny’s old “friend” is going to sleep on her couch through the weekend. However, when the anger between Leonard and Penny continue over to Howard and Raj, the whole group is almost divided; Sheldon (the only one not involved in any fight) takes the position of peacemaker.

48 :03x08 - The Adhesive Duck Deficiency

Leonard, Howard and Raj are on a camping trip in the desert to see the Leonid meteor shower, while Sheldon is at home enjoying the thought of being alone. But his night takes a turn when Penny needs medical help when she fell in the shower and dislocated her shoulder, making Leonard her only rescue. Meanwhile, the guys in the desert are drunk and accidentally eat their way to being foodless.

49 :03x09 - The Vengeance Formulation

Sheldon decides to use his great mind to come up with the perfect prank to pull on Kripke after he was humiliated on National Radio because Kripke had put helium in Sheldon’s office (making his voice girly while on the radio). However, Sheldon uses many attempts, but can’t come up with a great scheme to pull back on Kripke, until a science experiment comes to his mind (which involves dropping lots and lots of foam from the ceiling right down on Kripke while recording the video to YouTube). Meanwhile, Howard is unsure if he wants to continue his relationship with Bernadette when he finds out she wants a commitment while he just wants sex.

50 :03x10 - The Gorilla Experiment

Howard has regrets about introducing Bernadette to the others when she and Leonard really start to get along; forcing him into an uncomfortable position in which he will do anything to separate them again. Meanwhile, Penny sees the connection between Bernadette and Howard and she wants to learn what Leonard’s job really is about. However, her only choice for help is Sheldon, who isn’t the best teacher for those not so interested in science.

51 :03x11 - The Maternal Congruence

Leonard’s mother, Beverly, returns for another visit. Leonard is still not pleased with her coming over, while Sheldon is ecstatic. Penny, however, stresses over the fact that Leonard hasn’t told his mother that he is in a relationship with Penny, and she waits for the perfect moment to tell her, which seems to only be when Beverly becomes drunk for the first time. Meanwhile, Sheldon and Leonard are having friendship issues when it turns out Sheldon has been keeping frequent contact with Beverly while Leonard has been left out.

52 :03x12 - The Psychic Vortex

When Leonard and Howard go on a double date with Penny and Bernadette, Rajesh becomes the fifth wheel, and decides to seek a hook-up going to a university mixer accompanied by Sheldon (who was looking forward to spending his time alone, but was dragged alongside Raj.) However, when they score and get two girls back to their apartment, their week takes an unexpected turn. Meanwhile, Leonard learns that Penny believes in psychics, and his frustration over it causes her to dislike him. The only way Leonard can get Penny back now, is to meet the psychic and see how real it is.

53 :03x13 - The Bozeman Reaction

Returning from a dinner with the rest of the guys, Leonard and Sheldon are shocked to get back to a robbed apartment. Fearing the criminals will return, Sheldon becomes paranoid and locks himself in his room during the night. Realizing something has to be done, they get help from Howard and Rajesh in order to create a state-of-the-art security system that will attack any criminals that try to enter their apartment in the future. However, the security system can't help Sheldon's paranoid reaction to the breaking-and-entering, causing him to move to Bozeman, Montana, but will he return?

54 :03x14 - The Einstein Approximation

When Sheldon starts suffering from "theorist's block" and can't complete a formula, he becomes depressed and is willing to do anything to find the right answer. He tries several techniques to find the answer, but none of them works, but when he figures out how to figure the answer out, he starts working at the Cheesecake Factory with Penny (much to her dismay). However, it turns out Sheldon is like the perfect employee, even passing Penny in the number of customers.

55 :03x15 - The Large Hadron Collision

After being invited to Switzerland to see the CERN Supercollider (the world's largest and highest-energy partile accelerator), Leonard wants Penny to join him on the travel, making it a romantic Valentine's Day getaway. Sheldon becomes shocked that he can't go when he has a far bigger interest in the science, and tries to change Leonard's mind in all sorts of ways. Meanwhile, Leonard fears that no matter which of them he'll pick, the other will be angry and he will lose a friendship... or a relationship.

56 :03x16 - The Excelsior Acquisition

Ruining his one and only chance at meeting Stan Lee, Sheldon winds up in traffic court because of illegal driving that he did when he drove Penny to the hospital (episode 308). However, as Leonard, Howard and Raj are all going to see Stan Lee, Penny is Sheldon's only hope of avoiding jail.

57 :03x17 - The Precious Fragmentation

The guys buy a box of junk at a garage sale and find something precious inside, a prop ring from The Lord of the Rings that causes friend to go against friend.

58 :03x18 - The Pants Alternative

Sheldon wins an award and is reluctant to accept it since he must give a speech before a large crowd. Each of his friends tries to help in his/her own way.

59 :03x19 - The Wheaton Recurrence

Leonard's relationship with Penny hits rocky water after he utters the "L" word.

60 :03x20 - The Spaghetti Catalyst

With Leonard and Penny now split-up, Sheldon becomes the peacemaker.

61 :03x21 - The Plimpton Stimulation

Sheldon has a famous female physicist friend stay with he and Leonard and becomes upset when Leonard and his friend become intimate.

62 :03x22 - The Staircase Implementation

Leonard and Sheldon's argument leads to Leonard sleeping on Penny's couch and relating how he met Sheldon. The story of the broken elevator also is revealed.

63 :03x23 - The Lunar Excitation

Penny realizes that after dating Leonard, she can no longer put up with the guys of limited intelligence that guys she normally dates. Howard and Raj try to find Sheldon a date on the Internet.

64 :04x01 - The Robotic Manipulation

Howard borrows a robotic arm from work and finds himself in a bind, literally. Sheldon goes on a real date with his new friend Amy and Penny helps.

65 :04x02 - The Cruciferous Vegetable Amplification

Sheldon obsesses over his limited lifespan and takes steps to ensure he will stay alive until it is possible to have his consciousness downloaded into a robot.

66 :04x03 - The Zazzy Substitution

Sheldon misses his friendship with Amy and turns to feline companionship, to the dismay of all.

67 :04x04 - The Hot Troll Deviation

Howard's secret fantasies are revealed while Sheldon and Raj battle at the office.

68 :04x05 - The Desperation Emanation

All of the guys have girlfriends except Leonard, even Sheldon, who is anxious to be rid of Amy.

69 :04x06 - The Irish Pub Formulation

When Raj's sister comes to town, Leonard rekindles a romance with her and seeks to keep that information secret from Raj with the voluntary help from Sheldon.

70 :04x07 - The Apology Insufficiency

Howard's new project requires he get a security clearance and Sheldon's interview during the background check causes trouble.

71 :04x08 - The 21-second Excitation

The guys decide to wait in line for a special screening of Raiders Of The Last Ark while the girls pass and have a slumber party.

72 :04x09 - The Boyfriend Complexity

Penny's father shows up and she asks Leonard for help by pretending to still be her boyfriend. Bernadette joins Howard and Raj spend the night using a telescope as part of an astronomy project.

73 :04x10 - The Alien Parasite Hypothesis

A chance encounter with Zack, one of Penny's ex-boyfriends triggers an emotional response in Amy. Howard and Raj compete to decide who is a better superhero.

74 :04x11 - The Justice League Recombination

After insulting Zack, Penny's new/old boyfriend, the guys make friends and ask him to help with their entry into a costume contest.

75 :04x12 - The Bus Pants Utilization

Leonard has an idea for a smartphone app but as usual Sheldon wants to take over. After being kicked off the team, Penny tries to play peacemaker.

76 :04x13 - The Love Car Displacement

The group goes on a road trip to attend a science event and Howard is dismayed when Bernadette encounters an ex.

77 :04x14 - The Thespian Catalyst

Sheldon turns to Penny for acting lessons as a way to improve as a teacher. Raj has inappropriate fantasies about Bernadette.

78 :04x15 - The Benefactor Factor

The guys attend a formal dinner to try to persuade wealthy patrons to donate to the physics department. Leonard has to decide how far he will go when a particular donor shows an interest in him.

79 :04x16 - The Cohabitation Formulation

Howard and Bernadette consider moving in together; Leonard resumes dating Raj's sister, over Raj's vehement objections.

80 :04x17 - The Toast Derivation

Sheldon decides to invite new friends over when Leonard and the rest of the gang move their gatherings to Raj's place.

81 :04x18 - The Prestidigitation Approximation

Priya asks Leonard to choose between her and his friendship with Penny. Howard shows Sheldon a magic trick that Sheldon is determined to figure out.

82 :04x19 - The Zarnecki Incursion

After Sheldon's World of Warcraft account is hacked, the guys take it upon themselves to confront the culprit.

83 :04x20 - The Herb Garden Germination

Sheldon and Amy spread gossip about various members of the group as a social experiment. Howard must decide whether to pop the question to Bernadette.

84 :04x21 - The Agreement Dissection

Priya's increased presence at Leonard and Sheldon's apartment causes changes that Sheldon struggles with. To relax, he accompanies Penny and the girls on a night out with dancing.

85 :04x22 - The Wildebeest Implementation

Amy convinces Penny and Bernadette to use Bernadette as an undercover informant on Leonard and Priya's relationship. Raj decides to try out a new drug to cure his social anxiety disorder, but the results are less than satisfactory.

86 :04x23 - The Engagement Reaction

Howard musters up the courage to tell his mother that he is going to marry Bernadette. The news doesn't sit well and she ends up in the hospital.

87 :04x24 - The Roommate Transmogrification

Bernadette becomes the latest person in the group to receive her Ph.D., which leads to Howard being teased about his lack of the same. When Leonard starts spending the night with Raj's sister, Raj resorts to becoming a temporary roommate of Sheldon's.

88 :05x01 - The Skank Reflex Analysis

Penny must deal with the aftermath of her night with Raj and how it affects her friendship with the guys. Sheldon names himself captain of the paintball team and tries to assert his leadership.

89 :05x02 - The Infestation Hypothesis

Sheldon insists Penny rid her apartment of a piece of "found" furniture and tries to use Amy as a go between. Leonard and Priya try to make their long distance relationship with spicy video chats.

90 :05x03 - The Pulled Groin Extrapolation

Leonard accompanies Amy as her date to a wedding and ends up having fun in spite of himself. Bernadette tries spending the weekend with Howard and his mother in their house.

91 :05x04 - The Wiggly Finger Catalyst

Raj is so depressed he is alone so Penny finds him a girl he can talk to, so to speak.

92 :05x05 - The Russian Rocket Reaction

Sheldon's arch nemesis invites the guys to a party at his house and Leonard decides to go, angering Sheldon. Howard gets the opportunity of a lifetime but his decision doesn't sit well with Bernadette.

93 :05x06 - The Rhinitis Revelation

Sheldon's mom comes to town for a visit and Sheldon is angry that she doesn't want to cook and spend all her time with him. Instead, she chooses to spend most of her time with Leonard and the rest of the gang as they show her the town.

94 :05x07 - The Good Guy Fluctuation

Leonard is tempted to stray on Priya when a cute girl comes on to him at the comic book store. The guys pull a Halloween prank on Sheldon and he vows revenge.

95 :05x08 - The Isolation Permutation

Sheldon must suffer the responsibility to comfort Amy when Penny and Bernadette exclude her from their pre-wedding shopping.

96 :05x09 - The Ornithophobia Diffusion

Leonard and Penny decide to spend a night out just being friends. Sheldon freaks out when a bird haunts the apartment.

97 :05x10 - The Flaming Spittoon Acquisition

Sheldon must step up his game with Amy when she decides to go out with Stuart from the comic book store.

98 :05x11 - The Speckerman Recurrence

To Leonard's surprise, a bully from his high school days and his own personal tormentor gets in touch with him and Leonard must decide on a course of action. The girls try to help Penny make amends for her own history of being a bully.

99 :05x12 - The Shiny Trinket Maneuver

Amy is upset with Sheldon and his dismissal of her career accomplishments. Howard is dismayed by Bernadette's apparent disinterest in kids.

100 :05x13 - The Recombination Hypothesis

Out of the blue, Leonard invites Penny out on a date and they struggle with what it means.

101 :05x14 - The Beta Test Initiation

Leonard proposes that he and Penny treat their dating like software development and report "bugs" to each other. Raj gets a new phone, and falls in love with the AI contained within.

102 :05x15 - The Friendship Contraction

Leonard finally tires of Sheldon's thankless demands on him and breaks the friendship agreement. Howard and Raj brainstorm a way to make the other NASA astronauts pick a cool nickname for Howard.

103 :05x16 - The Vacation Solution

Sheldon's is required to take some vacation time away from work, and Amy pays the price. A pre-nuptial agreement rears its ugly head between Howard and Bernadette.

104 :05x17 - The Rothman Disintegration

Sheldon and his nemesis Kripke both want an office that becomes available with the retirement of a senior physicist. Amy gives Penny a heartfelt gift that Penny abhors, but how does she tell Amy without hurting her?

105 :05x18 - The Werewolf Transformation

When Sheldon's barber becomes unavailable due to illness, it starts the descent of his orderly life into chaos. Astronaut training proves more difficult for Howard than expected.

106 :05x19 - The Weekend Vortex

The guys decide to spend the weekend playing video games like they used to. The women in their life have other ideas however, especially Amy who is counting on Sheldon accompanying her to a family event.

107 :05x20 - The Transporter Malfunction

Raj finally gives up and asks his parents for help to find a wife. Sheldon's conscience causes him to hear his toy Spock doll speak to him.

108 :05x21 - The Hawking Excitation

Howard takes advantage of Sheldon's obsession to meet visiting professor Stephen Hawking by putting him through the ringer.

109 :05x22 - The Stag Convergence

Howard's bachelor party results in Bernadette learning things about Howard's past that makes her reconsider marrying him.

110 :05x23 - The Launch Acceleration

Howard's mission into space gets rescheduled sooner, creating a conflict with the wedding. Leonard and Penny resume their physical relationship until Leonard says something he shouldn't in the boudoir. Amy uses psychology on Sheldon to bring them closer together.

111 :05x24 - The Countdown Reflection

Bernadette decides she wants to be married to Howard before his mission to space. The gang scrambles to get it done.

112 :06x01 - Season 6, Episode 1