The Big Bang Theory

The Bad Fish Paradigm

Penny opens up to a reluctant Sheldon after a less-than-stellar first date with Leonard, placing him in the uncomfortable position of having to keep a secret.

The Codpiece Topology

Seeing Penny with another guy sends Leonard back to Leslie Winkle, much to Sheldon's dismay.

The Barbarian Sublimation

Penny becomes addicted to an online game based on the world of Conan the Barbarian and persistently pesters Sheldon for advice.

The Griffin Equivalency

Full of confidence following being named one of People's 30 to Watch Under 30, Raj hits on Penny and becomes impossibly arrogant.

The Euclid Alternative

An intervention is used to try to force Sheldon to overcome his fear of driving.

The Cooper-Nowitzki Theorem

Sheldon and his friends are mystified when a younger undergraduate student is attracted to him.

The Panty Pinata Polarization

When Sheldon bans Penny from the apartment for numerous minor infractions, she decides to retaliate. Howard and Raj search for the America's Next Top Model house.

The Lizard-Spock Expansion

Sheldon wants to use an alternate version of rock-paper-scissors to help resolve conflicts. A girl Wolowitz has a major crush on falls for Leonard.

The White Asparagus Triangulation

Sheldon is over-exuberant that Leonard finally has a girlfriend matching his high standards.

The Vartabedian Conundrum

Leonard seeks Penny's counsel when his relationship with Stephanie takes off faster than he'd like. Sheldon's hypochondriac tendencies get the better of him.

The Bath Item Gift Hypothesis

Sheldon irks the gangs with his obsession with proper Christmas gift protocol. Leonard's crushed when Penny dates a colleague of his.

The Killer Robot Instability

Penny's criticism of Wolowitz's romantic life pushes him into depression and AWOL for a fighting robot battle the rest of the guys are depending on him for.

The Friendship Algorithim

Looking to get friendly with Barry Kripke to gain access to a piece of high-tech lab equipment, Sheldon develops a flowchart process to make friends.

The Financial Permeability

When Sheldon loans money to Penny so she can pay her rent, it leads to Leonard coming face-to-face with her ex, Kurt.

The Maternal Capacitance

A visit from Leonard's mother ends up bringing him and Penny closer.

The Cushion Saturation

Paintball leads to a squabble between Sheldon and Penny as well as romance between Howard and Leslie.

The Terminator Decoupling

The gang is thrilled when they see Terminator: The Sarah Connor Chronicles' Summer Glau is also aboard their train to San Francisco for a scientific symposium. Sheldon frets over having forgotten a paper he wants to present to George Smoot.

The Work Song Nanocluster

Penny's business selling hair accessories out of her apartment gets out of hand when an over-caffeinated Sheldon takes charge.

The Dead Hooker Juxtaposition

Penny feels threatened when another sexy woman moves into the apartment building and angered when she senses the guys are being taken advantage of.

The Hofstadter Isotope

A fellow comic book enthusiast's hitting on Penny leads to Leonard, Raj and Howard going to a bar's Ladies' Night.

The Vegas Renormalization

Leonard and Raj take Wolowitz to Las Vegas to help him get over his break-up with Leslie. Sheldon, home alone and looking forward to it, locks himself out and has only one other place to stay: Penny's.

The Classified Materials Turbulence

Leonard is torn between being honest or self-serving when Stuart asks his advice for an upcoming second date with Penny. Wolowitz realizes there's a crucial error in a toilet he designed for the International Space Station.

The Monopolar Expedition

The guys receive a prestigious offer to work over the summer at the North Pole, and Penny's resultant behavior leaves Leonard unsure if he should go.

The Electric Can Opener Fluctuation

Discovering Leonard, Raj and Howard fudged the results of his Arctic research expedition, a disgraced Sheldon heads home to Texas.

The Jiminy Conjecture

Sheldon and Howard wager comic books over a cricket's species. Meanwhile, a less-than-perfect romantic night agonizes Leonard and Penny.

The Gothowitz Deviation

Howard takes Raj along to check out the Goth dating scene. Sheldon uses chocolate as part of a behavior modification experiment on Penny.

The Pirate Solution

Facing a return to India, Raj needs a job desperately enough to consider working for Sheldon. Meanwhile, Howard becomes a third wheel to Leonard and Penny.

The Creepy Candy Coating Corollary

Sheldon looks forward to squaring off against an actor from the Star Trek universe he holds enmity towards in a fantasy card game tournament. Wolowitz cashes in on an old pact with Leonard to get Penny to set him up with a friend of hers.

The Cornhusker Vortex

Leonard, hoping to fit in with Penny's football-loving friends, gets tutored in the sport by Sheldon. Raj is infuriated when Wolowitz's skirt-chasing leads to the loss of his prized patang.

The Guitarist Amplification

Leonard and Penny's first big fight sees Sheldon playing mediator due to childhood trauma that's left him with an inability to be around loud verbal conflicts.

The Adhesive Duck Deficiency

With the rest of the gang off on a desert camping trip to view the Leonid meteor shower, Sheldon must play hero after Penny slips in the tub and dislocates her shoulder.

The Vengeance Formulation

Barry Kripke pranks Sheldon during his spot on NPR, leaving him with a taste for vengeance. Wolowitz, pressured by Bernadette to define their relationship, gets advice from a fantasy version of Katee Sackhoff.

The Gorilla Experiment

Penny seeks Sheldon's help to better comprehend Leonard's physics work. Wolowitz sees green when Leonard invites Bernadette to watch an experiment.

The Maternal Congruence

A Christmas visit from his mother has Leonard discovering she's kept a lot of news from him that she shares with Sheldon and worrying if she'll approve of his romance with Penny.

The Psychic Vortex

Leonard is aghast to find out a secret of Penny's: she believes in psychics. Meanwhile, Sheldon tries to assist Koothrappali in picking up a girl at a university party.

The Bozeman Reaction

A robbery of their apartment sees Leonard and Sheldon call on their friends to devise a security system.

The Einstein Approximation

Stuck on the solution to a physics problem, Sheldon seeks a number of alternative approaches to change his thinking and free the mental block -- including working with Penny at The Cheesecake Factory.

The Large Hadron Collision

When Leonard is offered a trip to Switzerland on Valentine's Day to see a particle accelerator, he must choose between taking Penny or Sheldon.

The Excelsior Acquisition

An appearance in traffic court comes at the worst possible time for Sheldon, the same day Stan Lee is appearing at the comic book store.

The Precious Fragmentation

The guys go to a garage sale and find a ring from the Lord of the Rings films, and the rare find threatens their friendship.

The Pants Alternative

Sheldon's fear of speaking in front of large groups threatens his ability to accept an award, so the gang tries to help him get ready for the big night.

The Wheaton Recurrence

Sheldon gets to square off at the bowling alley against nemesis Wil Wheaton. Meanwhile, Leonard's miffed when Penny doesn't respond the way he hoped after saying "I love you."

The Spaghetti Catalysis

Subsequent to Leonard and Penny's break-up, Sheldon tries to hide from Leonard and the gang that he had a friendly spaghetti dinner at Penny's.

The Plimpton Stimulation

Sheldon hosts a visiting female physicist, but her intelligence seems matched by her libido.

The Staircase Implementation

A squabble over the thermostat setting leads to Leonard going over to Penny's and recounting for her the story of how he met and moved in with Sheldon.

The Lunar Excitation

Howard and Raj try to find the perfect match for Sheldon by setting him up on an Internet dating site. Seeing her new boyfriend interact with the gang makes it clear to Penny that she can't go back to dating dumb jocks after dating Leonard.

The Robotic Manipulation

Howard uses a robotic arm for his own pleasure. Sheldon goes on a date with Amy Farrah Fowler, his first date ever, and Penny finds herself accompanying them.

The Cruciferous Vegetable Amplification

Sheldon calculates that he'll be dead before technology exists to download his consciousness into a robot, so he goes on a binge of healthy living and ultra-safety.

The Zazzy Substitution

Sheldon breaks up with Amy Farrah Fowler, and the guys worry when he starts replacing her with cats.

The Hot Troll Deviation

Wolowitz is embarrassed when a secret of his is revealed, and Sheldon and Raj battle at work.

The Desperation Emanation

Sheldon meets Amy Farrah Fowler's mother and comes to the realization he no longer wants to see Amy, and Leonard realizes everyone is in a relationship except for him.

The Irish Pub Formulation

When Raj's sister has a one-day layover, he forbids the others from hooking up with her, unaware she and Leonard already did long ago.

The Apology Insufficiency

The rest of the gang is interviewed by the FBI for Wolowitz's security clearance with Sheldon accidentally letting slip some damaging information.

The 21-Second Excitation

The guys camp out in line to see a print of Raiders of the Lost Ark with 21 extra seconds and are outraged to see Wil Wheaton and his friends being allowed to skip the line. Penny and Bernadette invite Amy to their girls night.

The Boyfriend Complexity

Penny asks Leonard to lie to her visiting father, while Howard, Raj and Bernadette spend all night looking through a telescope.

The Alien Parasite Hypothesis

Amy crushes on one of Penny's dim ex-boyfriends, Zack. Raj and Wolowitz argue over who'd be the better superhero.

The Justice League Recombination

The guys get Zack and Penny to join their Justice League costume for a New Year's Eve bash at the comic book store.

The Bus Pants Utilization

Their friendship becomes strained when Sheldon tries to take over Leonard's creation of a smartphone application that solves differential equations.

The Love Car Displacement

Howard is jealous when Bernadette runs into her old boyfriend at a science event they're attending.

The Thespian Catalyst

Sheldon wants acting lessons from Penny, hoping they will make him a better teacher.

The Benefactor Factor

After meeting at a fundraising gala, an aged but wealthy Caltech donor makes Leonard ponder if he's willing to have sex with her to secure another donation.

The Cohabitation Formulation

Howard contemplates a serious decision in his relationship with Bernadette, and Leonard and Raj's sister start seeing each other again.

The Toast Derivation

Sheldon is in a crisis when he realizes he's not the epicenter of the group, so he decides to find new friends.

The Prestidigitation Approximation

Leonard has a tough choice to make when Priya asks him to stop spending time with Penny, forcing him to choose between the two women, and Howard keeps pestering Sheldon with a magic trick.

The Zarnecki Incursion

The guys become sleuths to find out who hacked Sheldon's online-game account.

The Herb Garden Germination

Sheldon and Amy decide to start rumors about themselves as a social test. Meanwhile, Howard takes his relationship with Bernadette to an even higher level.

The Agreement Dissection

Priya uses her legal expertise to rip apart Sheldon's roommate agreement, and the women take the flustered Sheldon out dancing.

The Wildebeest Implementation

Raj makes an attempt to cure his phobia of talking to women, and Penny spies on Leonard and Priya with the help of Bernadette.

The Engagement Reaction

Mrs. Wolowitz ends up in the hospital after Howard tells her he's marrying Bernadette. While there, Leonard stresses over Penny and Priya warming up to one another.

The Roommate Transmogrification

Raj moves in with Sheldon when Leonard and Priya's Star Trek bedroom fantasy is too much for him, and the guys tease Howard when Bernadette gets her PhD, making Howard the only one without a doctorate.

The Skank Reflex Analysis

On the fifth season premiere, Penny worries that she's screwed things up permanently with her friends after her night with Raj, while Sheldon takes command of the paintball team.

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 (Aarti Mann).

The Pulled Groin Extrapolation

Attending a co-worker's wedding, Leonard and Amy (Mayim Bialik) get to know each other better, while Howard and Bernadette spend the weekend with Mrs. Wolowitz!

The Wiggly Finger Catalyst

When Raj is upset he's the only one of the four guys who's not in a relationship, Penny sets out to find the perfect date, introducing him to Emily, a girl he can actually talk to!

The Russian Rocket Reaction

Sheldon and Leonard get invited to a housewarming party at Wil Wheaton's house. Howard gets an out-of-this-world opportunity!

The Rhinitis Revelation

Sheldon craves attention from his visiting mother.

The Good Guy Fluctuation

Sheldon tries to spook his friends on Halloween.

The Isolation Permutation

Bernadette & Penny shop for wedding dresses without Amy.

The Ornithophobia Diffusion

Sheldon must overcome his fear of birds.

The Flaming Spittoon Acquisition

Sheldon becomes jealous when Stuart asks Amy for a date.

The Speckerman Recurrance

Leonard comes face-to-face with his high school bully.

The Shiny Trinket Maneuver

Sheldon gets in trouble with Amy, 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.

The Recombination Hypothesis

Everything might change when Leonard offers Penny a spur of the moment invitation to a romantic dinner for two on the 100th episode of the series.

The Beta Test Initiation

Leonard and Penny "beta test" their relationship.

The Friendship Contraction

Sheldon's selfish demands force Leonard to reconsider their friendship. Meanwhile, Howard tries to pick his astronaut nickname. NASA astronaut Mike Massimino guest stars.

The Vacation Solution

When Sheldon is forced to take a vacation by the university, he goes to work with Amy in her neurobiology lab.

The Rothman Disintegration

When a corner office at the University opens up, Sheldon must compete for it with his office nemesis, Barry Kripke. Meanwhile, Penny receives an unusual gift from Amy.

The Werewolf Transformation

A change in Sheldon's routine forces him to re-evaluate his entire life, when his barber is sick. Meanwhile, Howard rethinks his decision to go into space after astronaut training.

The Weekend Vortex

Sheldon chooses to participate in a guys-only weekend Star Wars gaming marathon rather than go with Amy to her aunt's birthday party -- and gets a lesson from Penny and Amy.

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.

The Hawking Excitation

Sheldon has a chance to meet his hero, Stephen Hawking.

The Stag Convergence

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

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 (Casey Sander).

The Countdown Reflection

When Howard and Bernadette decide they want to be married before his NASA space launch, the gang rushes to put on a wedding, on the fifth season finale.

The Date Night Variable

On the sixth season premiere, Howard discovers that he can't escape his mother -- even in space! Back on earth, meanwhile, Raj turns his existence as a third wheel into an art form.

The Decoupling Fluctuation

When Sheldon learns that Penny is thinking about breaking up with Leonard, he tries to intervene. Meanwhile, Howard is being picked on in space by the other astronauts.

The Higgs Boson Observation

Amy's nervous when Sheldon hires Alex, a female assistant.

The Re-Entry Minimization

Howard returns from space -- without the welcome he wanted.

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.

The Extract Obliteration

Sheldon's friendship 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.

The Habitation Configuration

Bernadette pressures Howard to move out of his mother's house, while Sheldon finds himself caught in the middle of a fight between Amy and Wil Wheaton.

The 43 Peculiarity

Howard and Raj try to solve a mystery about Sheldon.

The Parking Spot Escalation

Sheldon and Howard battle over an assigned parking spot.

The Fish Guts Displacement

Howard bonds with his father-n-law on a fishing trip.

The Santa Simulation

Sheldon unwillingly revisits some Christmas memories during a lively game of Dungeons and Dragons, while Raj joins the girls for ladies night out.

The Egg Salad Equivalency

Sheldon is accused of sexual harassment at the University and winds up dragging Leonard, Raj and Howard into the fray.

The Bakersfield Expedition

Leonard's car is stolen when the guys take a road trip to a comic book convention in Bakersfield, dressed as Star Trek characters.

The Cooper/Kripke Inversion

Outraged that he's being forced to work with his university nemesis, Barry Kripke (John Ross Bowie), Sheldon faces a crisis of conscience.

The Spoiler Alert Segmentation

When Sheldon and Leonard fight, it affects Penny and Amy's living arrangements. Meanwhile, Raj takes care of Mrs. Wolowitz while Howard is away.

The Tangible Affection Proof

Sheldon struggles to find a Valentine's gift for Amy.

The Monster Isolation

Raj vows never to leave his apartment after a horrible date.

The Contractual Obligation Implementation

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.

The Closet Reconfiguration

To open or not to open? When Howard finds a letter from his father, he's forced to confront his past. And Leonard and Penny throw a grown-up cocktail party at the apartment.

The Tenure Turbulence

Leonard, Sheldon and Raj fight for tenure at the University.

The Closure Alternative

After one of his favorite TV shows gets canceled too soon, Sheldon feels lost, so Amy tries to help him get over his compulsive need for closure by retraining his brain.

The Proton Resurgence

Leonard and Sheldon hire Professor Proton (Bob Newhart), the host of their favorite childhood TV show to perform. Raj leaves his dog with Howard and Bernadette.

The Love Spell Potential

When the girls' trip to Vegas falls through, the guys invite them to a Dungeons & Dragons date night that causes Sheldon and Amy's relationship to take an unexpected turn.

The Bon Voyage Reaction

On the sixth season finale, Sheldon and Penny are thrown for a loop when Leonard is offered an exciting new job opportunity overseas.

The Hofstadter Insufficiency

Leonard is away at sea, so Sheldon and Penny spend time together and spill some revealing secrets. Meanwhile, Howard comes to Raj's aid after his breakup with his girlfriend.

The Deception Verification

Leonard returns from the North Sea expedition and finds things chilly between him and Sheldon, while Howard's relationship with his mother opens the door to questions about his masculinity.

The Scavenger Vortex

Raj puts together a scavenger hunt that turns into serious, cutthroat competition among the gang.

The Raiders Minimization

Sheldon is fit to be tied when Amy ruins one of his favorite adventure films, while Leonard finds the key to getting Penny to do his bidding, and Raj and Stuart get creative with their online-dating profiles.

The Workplace Proximity

Amy takes a job at Sheldon's university, putting their relationship to the test.

The Romance Resonance

Sheldon makes a major scientific breakthrough, but he feels it may haunt him for the rest of his career. Meanwhile, Howard makes a grand romantic gesture to Bernadette, which causes Penny to put more effort into her relationship with Leonard.

The Proton Displacement

When Sheldon's childhood hero, Professor Proton, seeks Leonard's help with an experiment, the slighted Sheldon goes nuclear and decides to get revenge by befriending another TV science guy.

The Itchy Brain Simulation

Leonard fails to stop Sheldon from overreacting after a past slight comes to light, and as punishment Leonard must walk a mile in Sheldon's shoes. Meanwhile, Penny has a run-in with Raj's former girlfriend Lucy.

The Thanksgiving Decoupling

Howard's mother has a say when he and Bernadette host Thanksgiving dinner for the gang.

The Discovery Dissipation

When Sheldon's accidental scientific discovery is disproved, Amy and Leonard try to help him deal with the shame and the disappointment. Meanwhile, Howard and Bernadette open their home to Raj for a week.

The Cooper Extraction

With Sheldon in Texas, the gang gathers to decorate for Christmas, and they each contemplate if they would have had a wonderful life had they never met him.

The Hesitation Ramification

Penny turns to Leonard for comfort after her guest appearance on NCIS does not turn out well. She ends up putting Leonard on the spot regarding their relationship. Sheldon works on his sense of humor, and Raj practices talking to girls.

The Occupation Recalibration

There's impactful news on the work front as Penny makes a big step toward pursuing a full-time acting career, and Sheldon is forced to take a vacation.

The Convention Conundrum

Unable to score tickets for Comic-Con, Sheldon decides to stage his own comic-book convention, while the ladies attempt to act like grown ups.

The Locomotive Manipulation

Amy has amour on her mind when she talks Sheldon into a romantic Valentine's Day getaway to Napa Valley wine country. Back at home, Leonard and Penny make an emergency visit to the vet with Raj's dog.

The Table Polarization

Leonard's purchase of a dining-room table for the apartment doesn't sit well with Sheldon, so much so that it forces him to reevaluate his life. Meanwhile, Bernadette isn't quite over the moon about Howard taking another trip to space.

The Friendship Turbulence

Things turn rocky between Sheldon and Wolowitz after a barrage of insults, and Bernadette steps in to mediate a peace. Meanwhile, Penny is offered a movie role that may prove embarrassing.

The Mommy Observation

While Sheldon and Howard continue their bonding, Sheldon's visit to see his mommy forces him to start addressing a new reality. The gang are subjected to a murder mystery party that leads them to speculate where they might be in 20 years.

The Indecision Amalgamation

Raj wrestles with dating two women at the same time, Penny is offered a part in a trashy movie, and Sheldon can't decide between two gaming systems.

The Relationship Diremption

Raj and Howard double-date, and the latter is flushed with embarrassment after Raj's girlfriend reveals a secret she knows about Howard.

The Anything Can Happen Recurrence

Leonard reinstates Anything Can Happen Thursday, and it leads the regimented Sheldon to attempt something spontaneous, which creates friction among Penny, Amy and Bernadette. Raj requests help from Howard in prepping for a date with Emily.

The Proton Transmogrification

Sheldon receives counseling from his childhood TV idol, Professor Proton, while Penny and Leonard reach a relationship milestone and turn it into a competition. Also, Bernadette and Amy turn Star Wars Day into a special event for the guys.

The Gorilla Dissolution

A trying day at the movie shoot leaves Penny with questions about her life choices, so she decides to act on it. Caring for a bedridden Mrs. Wolowitz proves a challenge for Howard and Bernadette.

The Status Quo Combustion

Sheldon gets caught up in all the life-altering changes going on around him and considers a monumental move.

The Locomotion Interruption

Amy and Leonard take a surprise road trip to Arizona, while Penny goes on a job interview at Bernadette's company, and Howard has problems wrapping his head around Stuart's relationship with Mrs. Wolowitz.

The Junior Professor Solution

Sheldon is ordered to teach a class, and the gang is surprised when Howard signs up to take it, and tensions between Penny and Bernadette afford Amy an opportunity to play one against the other.

The First Pitch Insufficiency

A nervous Wolowitz is thrown for a loop when NASA asks him to toss out the first pitch at a Los Angeles Angels baseball game. Meanwhile, Sheldon brags that he and Amy are a better couple than Leonard and Penny.

The Hook-Up Reverberation

Raj's girlfriend, Emily, gives Penny the cold shoulder after he reveals some info about their past history; and the guys contemplate buying into Stuart's comic-book emporium.

The Focus Attenuation

Amy and Bernadette accuse former party girl Penny of becoming a party pooper when she lets an email from work impact their girls' weekend in Las Vegas. Meanwhile, the guys brainstorm about inventing something cool.

The Expedition Approximation

Sheldon and Raj undertake an underground research expedition that turns into a test of how long before they get under each other's skin. Meanwhile, Leonard and Penny argue about money.

The Misinterpretation Agitation

Penny's flirtatious sales pitch leaves a doctor-client smitten and the guys must pitch in to help her deal with him, while Bernadette and Amy debate whether female scientists ought to play the sexuality card.

The Prom Equivalency

Amy and Bernadette organize a prom to be held atop the guys' apartment complex but Sheldon is leery of all the prom pomp, circumstance and romancing that goes with it.

The Septum Deviation

Leonard needs surgery for a deviated septum, and Sheldon gets his nose out of joint because he feels an operation is too dangerous and that his roommate may not make it out alive.

The Champagne Reflection

It's a banner day for Sheldon as he bids a sad farewell to his Fun With Flags podcast. Meanwhile, Leonard, Howard and Raj probe a late professor's research in search of some hidden significance.

The Clean Room Infiltration

On Christmas Eve, Amy plans a traditional Victorian dinner, while Raj, Leonard and Howard scramble to remove a pigeon that flew into the clean room at the university.

The Space Probe Disintegration

While Raj eagerly awaits data from a space probe in which he was involved, Howard keeps distracting him. Later, dress shopping with Penny and Amy doesn't exactly prove to be a good fit for Leonard and Sheldon.

The Anxiety Optimization

Sheldon becomes concerned that his cushy lifestyle is impacting his professional progress and keeping him from achieving scientific renown, so he asks the gang to make life more difficult for him.

The Troll Manifestation

An online troll rips Leonard and Sheldon's published physics paper, so the guys rally to defend the two and expose the bully, while a girls night out leads to Penny, Amy and Bernadette dishing about embarrassing past events.

The Comic Book Store Regeneration

Amid the excitement of Stuart reopening his comic-book store, Howard gets some unsettling news; and after teaching Sheldon how to "let it go," Penny doesn't practice what she preaches when she learns something maddening about Amy.

The Intimacy Acceleration

An experiment designed to make participants fall in love piques Penny and Leonard's interest, so they decide to put it to the test. Meanwhile, Leonard, Amy, Raj and Emily have an encounter with a "zombie."

The Colonization Application

There's trouble in paradise when Amy discovers Sheldon signed up for a one-way mission to colonize Mars, and the two get into a dogfight at a pet store. Meanwhile, Leonard makes a very "adult" purchase for Penny.

The Leftover Thermalization

An electrical short thaws the last meal that was cooked by Mrs. Wolowitz, and the gang ponders what to do with it, while Sheldon and Leonard's work is featured in a magazine, but only one receives credit.

The Skywalker Incursion

A speaking engagement at UC Berkeley puts Leonard and Sheldon in a galaxy not too far, far away from their idol George Lucas' Skywalker Ranch, and they considrer dropping by.

The Fortification Implementation

When Sheldon and Amy build a fort, they come to a crossroad in their relationship. Wolowitz is shocked when a man claiming to be his half-brother shows up. When Penny is invited to be on Wil's podcast, she and Leonard have an argument.

The Communication Deterioration

In the event of alien contact, NASA asks Raj to craft a message for the extraterrestrials, and the guys battle over how it should be handled. Meanwhile, Penny must decide between auditioning for a film role or keeping her job in pharmaceutical sales.

The Graduation Transmission

Wolowitz questions his abilities when he and Sheldon can't get a drone to fly. A canceled flight nearly prevents Leonard from giving the commencement address. Raj pits his parents against each other when his father cuts him off financially.

The Maternal Combustion

Leonard and Sheldon's mothers come to town to celebrate their sons getting an award, but the opinionated women engage in an altercation over religion.

The Commitment Determination

In the Season 8 finale, Leonard and Penny are pressured to set a wedding date by Sheldon, whose relationship with Amy has taken an interesting turn.

The Matrimonial Momentum

Season 9 premiere, Penny has a problem dealing with Leonard's confession about having kissed another woman, while Sheldon is confused about Amy calling a timeout on their relationship.

The Separation Oscillation

To ease Penny's mind, Leonard pays a visit to the woman he kissed during his expedition to the North Sea, while Sheldon's breakup with Amy leads him to retaliate by shooting a special episode of "Fun with Flags".

The Bachelor Party Corrosion

The guys surprise Leonard with a belated bachelor-party weekend in Mexico, but their plans hit a bump in the road when they get a flat tire on the way. Meanwhile, the girls lean on Penny to tell her family that she and Leonard eloped.

The 2003 Approximation

Sheldon reverts back to 2003 when he learns that Leonard and Penny are moving in together. Meanwhile Howard and Raj form a band to play at the comic book store.

The Perspiration Implementation

When Barry Kripke gives the guys fencing lessons, he makes a point of letting Sheldon know he's interested in dating Amy. Stuart has trouble getting female customers at the Comic Book Store, so Penny, Amy and Bernadette stop by to help out.

The Helium Insufficiency

A helium shortage leads Sheldon and Leonard to do business with a dealer in the black market in order to acquire some of the element for an experiment they need to complete.

The Spock Resonance

Sheldon's interview for a "Star Trek" documentary focusing on Spock turns up a shocking revelation about his breakup with Amy. Meanwhile, the Wolowitzes haggle over the remodeling of his family home.

The Mystery Date Observation

When Leonard, Penny and Bernadette learn that Amy is going out on a dinner date, the trio set out to spy on her and the guy. Meanwhile, Sheldon recruits Raj and Howard to find a woman for him.

The Platonic Permutation

Now just friends, Sheldon and Amy spend Thanksgiving at the aquarium, a reluctant Wolowitz volunteers at a soup kitchen with Bernadette, Raj and Emily, and Penny realizes that Leonard knows a bit more about her than he's let on.

The Earworm Reverberation

God only knows what song is constantly playing in Sheldon's head, but it reminds him of Amy and leads to a surprising revelation. Meanwhile, she is back in the dating game.

The Opening Night Excitation

Professor Proton visits Sheldon in a dream and gives him Obi-Wan Kenobi-like advice about whether to go see the new "Star Wars" film or spend the time with newly reunited girlfriend Amy on her birthday.

The Sales Call Sublimation

Penny entices Leonard to meet with a psychiatrist and the results are surprising, Stuart moves out of the Wolowitz house, and Howard and Bernadette find themselves at a loss.

The Empathy Optimization

Dealing with an under-the-weather Sheldon is so draining for Penny, Leonard, and the gang, that they decide to treat themselves to a Sheldon-less weekend.

The Meemaw Materialization

Sheldon's grandmother, aka Meemaw, visits and there's friction between her and Amy, which intensifies after the elderly woman blurts out a secret about Sheldon.

The Valentino Submergence

Sheldon and Amy celebrate Valentine's Day with an episode of Fun With Flags, Leonard and Penny feel the pangs of aging, and Howard and Bernadette are surprised by what they find in their hot tub.

The Positive Negative Reaction

The gang learns Bernadette is pregnant and celebrates by singing karaoke. Meanwhile, Wolowitz freaks out over the pregnancy announcement and becomes convinced he must make more money to provide for the baby.

The Celebration Experimentation

Sheldon and the gang celebrate his birthday and he's surprised by a special guest.

The Application Deterioration

Howard reconsiders entering into a legal partnership with Leonard and Sheldon regarding the patent for the infinite persistence gyroscope. Also, the women offer Raj dating advice after Emily reaches out to him following their breakup.

The Solder Excursion Diversion

Sheldon shocks Amy with a startling revelation after she buys him a new laptop. Meanwhile, Raj throws Leonard and Howard under the bus after they lie to their wives and sneak off to an early screening of a movie.

The Big Bear Precipitation

Sheldon shares a secret about Leonard when the two go on a weekend trip with Penny and Amy; Raj goes all out with pregnancy gifts.

The Viewing Party Combustion

During a group get-together, a minor argument between Sheldon and Leonard turns into a heated debate, leaving the rest of the gang to choose sides.

The Fermentation Bifurcation

Sheldon stays behind to spend quality time with the pregnant Bernadette when the rest of the gang toddles off to a wine-tasting event where they run into Penny's former boyfriend, and Raj introduces his new girlfriend.

The Line Substitution Solution

When Sheldon decides he'd rather go to a movie screening than hang out with Amy, he hires Stuart to spend the day with her. Meanwhile Leonard's mother visits, and Penny just can't seem to connect with her.

The Convergence Convergence

In the Season 9 finale, Leonard's recently divorced parents roll into town, as does Sheldon's holy-roller mother, and all hell breaks loose.

The Conjugal Conjecture

In the Season 10 premiere, the gang deals with the awkward aftermath of an overnight liaison between Sheldon's mother and Leonard's father. Meanwhile, Penny's dysfunctional family is in town for the wedding.

The Military Miniaturization

The guys heads are in a spin when an Air Force bigwig approaches them about their revolutionary gyroscope invention, and Bernadette is upset with Penny after she accidentally leaks a secret to the mom-to-be's coworkers about her being pregnant.

The Dependence Transcendence

Howard and Leonard are putting in late nights at work and Sheldon is having trouble keeping up, Raj and a pregnant Bernadette spend a day together, and Penny and Amy take in a faculty party.

The Cohabitation Experimentation

Sheldon and Amy decide to move in together when her apartment floods. Meanwhile, Howard and Bernadette become upset when Raj learns the gender of their baby before they do.

The Hot Tub Contamination

Amy and Sheldon's live-in relationship may be in the toilet after he accuses her of not following the bathroom schedule. Meanwhile, Howard and Bernadette's secret staycation is interrupted by interfering interlopers who are sneaking into their hot tub.

The Fetal Kick Catalyst

Feeling his fetal offspring kick sends Howard on a baby-items buying binge with Raj, Sheldon and Amy host a brunch in their new digs, and Penny, by virtue of her virtuoso performance in "Serial Apist," is invited to a sci-fi convention.

The Veracity Elasticity

In order to remain Sheldon's roomie, Amy fibs about repairs being made to her apartment. Later, they present a episode of "Fun with Flags" in Penny's apartment.

The Brain Bowl Incubation

A successful gene experiment leaves Sheldon excited to procreate with Amy, and he pulls out all stops to get her on board. Meanwhile, Raj is reluctant to reveal what the new woman in his life does for a living.

The Geology Elevation

A geologist coworker's MacArthur Genius fellowship award leaves Sheldon stone cold jealous. Meanwhile, Howard stumbles upon a remote-control Stephen Hawking action figure that he invented. Hawking appears as himself.

The Property Division Collision

A great divide develops between Sheldon and Leonard when it comes time to divvy up their shared belongings. Meanwhile, with Bernadette heading into her pregnancy homestretch, Raj and Stuart battle to be the one providing her the most help.

The Birthday Synchronicity

The Wolowitz baby arrives, while Sheldon and Amy celebrate Amy's birthday.

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.

The Romance Recalibration

After a marital disagreement, Penny takes off for a spa weekend with Amy, and Sheldon steps in to play peacemaker for the squabbling newlyweds. Meanwhile, Howard and Raj do battle with a noisy floor in the baby's room.

The Emotion Detection Automation

Sheldon decides to test an MIT invention that can help read people's emotions. Meanwhile, Leonard has trouble hiding his emotions when Penny announces her brother is going to visit, and Raj gathers former girlfriends to ask for their dating advice.

The Locomotion Reverberation

With Sheldon hindering progress on the guidance-system project, Leonard and Stuart figure the only way they can get back on track is to engineer a distraction by getting him tickets to a historic railroad.

The Allowance Evaporation

Amy is incensed when she discovers Sheldon has shared intimate relationship information with people at the University, and Raj is knocked for a loop when his father stops sending financial support.

The Comic-Con Conundrum

Without financial backing from his father, Raj finds himself in a cash crunch and turns to Sheldon to help him get his head above water. Meanwhile, Penny considers crashing the guys' annual Comic-Con getaway.

The Escape Hatch Identification

Leonard and Penny offer Sheldon's old room to Raj after he moves out of his apartment.

The Collaboration Fluctuation

Raj moves in with Leonard and Penny and a period of adjustment begins for the three, while usually self-centered Sheldon shows surprising interest in Amy's work.

The Recollection Dissipation

Sheldon is working overtime and pushing himself when he collaborates on projects with Leonard and Howard, and another one with Amy, all on the same day. Bernadette's maternity leave is running out and she must face going back to work.

The Separation Agitation

Leaving baby Halley in day care proves to be tough for Bernadette after she starts back to work, and geologist Bert digs up a girlfriend, but some of his colleagues think she's a gold digger.

The Cognition Regeneration

Penny's job offer from a former boyfriend doesn't sit well with Leonard.

The Gyroscopic Collapse

Leonard, Sheldon and Wolowitz celebrate the successful completion of their top-secret military project, until an unpleasant surprise leaves their heads spinning. Amy considers an offer of a summer position as a visiting researcher.

The Long Distance Dissonance

On the Season 10 finale, Sheldon's former admirer, Dr. Ramona Nowitzki, turns up while Amy is visiting Princeton, and the gang is extremely concerned.

The Proposal Proposal

Season 11 begins with Amy giving Sheldon an answer to his marriage proposal. Meanwhile, Howard and Bernadette struggle with some unexpected news.

The Retraction Reaction

Leonard angers the university and the entire physics community when he gives an embarrassing radio interview. Meanwhile, Amy and Bernadette bond over having to hide their success from Sheldon and Howard.

The Relaxation Integration

Amy records Sheldon talking in his sleep and tries to convince him that he has a more laid-back side. Meanwhile, Raj and Stuart compete to win the heart of Bernadette's new co-worker.

The Explosion Implosion

Wolowitz and Sheldon bond over their relationships with their disappointing fathers when they drive to the desert to shoot off a model rocket. Leonard's mom finds a new best friend in Penny, much to Leonard's dismay.

The Collaboration Contamination

Sheldon and Raj confide in Bernadette when they can't handle Amy and Howard working together. Penny and Leonard learn new tactics on how to deal with Sheldon and they come from an unlikely source.

The Proton Regeneration

Sheldon goes head-to-head with Wil Wheaton for the role of the new Professor Proton. Penny steps in and takes care of Halley when Bernadette and Howard both wind up on bed rest.

The Geology Methodology

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

The Tesla Recoil

Leonard and Howard are furious after they learn Sheldon went to work with the military behind their backs. Bernadette is on bed rest, and she asks Raj to do some digging when she suspects Ruchi is trying to steal her job.

The Bitcoin Entanglement

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

The Confidence Erosion

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

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.

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. Also, Penny reveals her true feelings about Amy.

The Solo Oscillation

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

The Separation Triangulation

Raj learns the woman he's dating has a very upset husband. Sheldon rents his old room for a quiet place to work.

The Novelization Correlation

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

The Neonatal Nomenclature

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

The Athenaeum Allocation

Leonard jumps through hoops to help secure the perfect wedding venue for Sheldon and Amy. Bernadette and Howard have a hard time deciding who should stay home with the kids and who should go back to work.

The Gates Excitation

Penny gets the opportunity to host Bill Gates at work when his company wants to partner with her pharmaceutical company. Leonard, Raj and Howard do everything in their power to meet him, while Sheldon thinks he is the victim of an April Fools' prank.

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.

The Reclusive Potential

Reclusive scientist, Doctor Wolcott, invites Sheldon to his cabin in the middle of nowhere, and Leonard, Raj and Howard go along. Penny and Bernadette improvise after Amy doesn't like the tame bachelorette party they planned for her.

The Comet Polarization

Sheldon's comic book store experience changes when writer Neil Gaiman puts Stuart's store on the map. Raj takes credit for Penny's astronomical discovery, and friendships are threatened.

The Monetary Insufficiency

Sheldon goes to Vegas to win money for science. Penny and Bernadette take Amy wedding dress shopping, but her terrible choice entangles them in a web of lies.

The Sibling Realignment

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

The Bow Tie Asymmetry

In the Season 11 finale, when Amy's parents and Sheldon's family arrive for the wedding, everybody is focused on making sure all goes according to plan -- everyone except the bride and groom.

The Conjugal Configuration

Sheldon and Amy's honeymoon runs aground in New York, while Penny and Leonard discover they are uncomfortably similar to Amy's parents, Mr. and Mrs. Fowler. Raj insults physicist Neil deGrasse Tyson and starts a twitter war.

The Wedding Gift Wormhole

Sheldon and Amy drive themselves crazy trying to figure out what "perfect gift" Leonard and Penny gave them for their wedding. Raj decides he wants to settle down and asks his father to arrange a marriage for him.

The Procreation Calculation

Howard's life gets complicated when Stuart starts bringing his new girlfriend home. Penny and Leonard talk about starting a family while Raj explores an arranged marriage.

The Tam Turbulence

Sheldon won't tell anyone why he's never mentioned Tam, his childhood best friend, so Leonard takes matters into his own hands. Bernadette and Penny take out Raj's fiance, Anu, for dinner to get the skinny on her.

The Planetarium Collision

Amy doesn't have time to work on a project, so Sheldon goes to great lengths to ensure she can work with him even if it means sabotaging her career in the process. Raj doesn't want Howard to join him in hosting a show at the planetarium.

The Imitation Perturbation

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

The Grant Allocation Derivation

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

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. Raj and Anu try to get physical for the first time.

The Citation Negation

Sheldon and Amy are devastated learning from a Russian paper that Super Asymmetry has been discovered and disproven. Ultra-competitive Bernadette asks Stuart's girlfriend, Denise, to teach her how to beat Howard in a popular videogame.

The VCR Illumination

Sheldon and Amy are still down about their theory being disproven, but a VHS tape from Sheldon's past inspires him not to give up. Bernadette turns into a pageant mom when she tries to help Howard ace his Magic Castle audition.

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.

The Propagation Proposition

Penny's ex-boyfriend, Zack, and his wife want a baby, but when Zack is infertile, they ask Leonard to help. Raj attempts to mend things with his ex-fiancée, Anu.

The Confirmation Polarization

Sheldon and Amy's super asymmetry theory is proven by two physicists, Dr. Pemberton and Dr. Campbell from Chicago, who then try to kick Amy off the Nobel nomination. Bernadette has a big success at work, and Penny's going to be a part of it.

The Meteorite Manifestation

Sheldon is thrilled to help Bernadette and Howard navigate bureaucratic paperwork, until he discovers they are breaking the law. Leonard is disappointed when his friends exclude him from a scientific project.

The Donation Oscillation

Penny tries to seduce an abstaining Leonard to ruin his "donation" for her ex-boyfriend, Zack, and his wife, Marissa. Howard, Bernadette, Anu and Raj turn Raj's canceled bachelor party into a couple's trip aboard the "vomit comet."

The D & D Vortex

The gang finds out Wil Wheaton hosts a celebrity Dungeons and Dragons game involving William Shatner, Joe Manganiello, Kareem Abdul-Jabbar and Kevin Smith. Deception and betrayal are the path to make it to the one open seat.

The Conference Valuation

Penny and Bernadette go to San Diego for a pharmaceutical sales convention, leaving Howard in charge of the kids. Sheldon finds a book on experimenting on kids, and the guys plus Amy make a day of it.

The Laureate Accumulation

Pemberton and Campbell charm America on a publicity tour, so Sheldon and Amy bring Nobel laureates Kip Thorne, George Smoot and Frances Arnold to their side. Halley's fear of the dark leads to conflict for Howard, Bernadette and Stuart.

The Inspiration Deprivation

Amy has a meltdown due to the pressure associated with winning a Nobel Prize. Raj and Howard try to relive the good old days after Howard buys a scooter that looks like the one he had years ago.

The Decision Reverberation

Raj is worried people won't take him seriously in his own field after publishing a paper that suggests he may have discovered alien life. Leonard wants to be the principal investigator on a plasma physics study.

The Plagiarism Schism

Kripke has proof that Dr. Pemberton plagiarized his thesis, and Sheldon and Amy aren't sure whether they should turn him in or not. Howard is surprised to learn that Bernie wasn't the only waitress at the Cheesecake Factory who had a crush on him.

The Maternal Conclusion

Leonard is pleasantly surprised when Beverly comes to visit and she's genuinely kind to him, until he finds out the real reason she's there. Denise and Stuart overstay their welcome at the Wolowitz house.

The Change Constant

Amy and Sheldon wait for the news. Howard and Bernadette leave their kids. Leonard and Penny keep a secret.

The Stockholm Syndrome

Bernadette and Howard leave their kids for the first time, Penny and Leonard 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.