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For the pilot episode of Young Sheldon please see Pilot (Young Sheldon).

The Pilot is the series premiere of the American sitcom The Big Bang Theory. This episode first aired on Monday, September 24, 2007.


Leonard and Sheldon are two brilliant physicists who live together and work together at Caltech. Upon returning home one day, they spot their gorgeous new neighbor Penny, whom Leonard immediately develops a crush on and becomes friends with.

Extended Plot

Leonard and Sheldon go to a High I.Q. sperm bank to make donations and earn some money. To get the attention of the receptionist,

Penny First Look

Leonard's first view of Penny.

Leonard very quickly solves all her crossword puzzle for her, which does not please her. She has them fill out their forms, but they back out after Sheldon informs Leonard that "there is no guarantee that our sperm is going to generate high I.Q. offspring", ergo, they are committing genetic fraud. (This scene is not usually aired on reruns.)

Upon returning to their apartment, they climb the stairs while Sheldon tells Leonard that if the stairsteps are off by two millimeters most people will trip. Doing his experiment he tripped his father and broke his clavicle. At the top of the stairs, they spot Penny, who is moving into the apartment across the hall from them. Leonard and Sheldon agree that she is an improvement over their old neighbor, Louie/Louise, who, according to Sheldon, was a 200-pound transvestite with a skin condition. After Penny spots them, they exchange two rounds of "hi". Penny learns that they are her neighbors from across the hall. She offers to have coffee with them later.

Back home, Leonard thinks they should invite her over for lunch though Sheldon tells him that, except for Howard and Raj, people don't come over. Penny is invited over to their apartment after a round-about invitation that includes mentioning the health of one's colon.


First time in their apartment.

Penny enters their home and looking over Sheldon's whiteboard, she is impressed by their work. It includes some quantum mechanics, a little string theory doodling around the edges and a joke on the Born-Oppenheimer approximation. Sheldon agrees on Penny's suggestion that he is one of those "Beautiful Mind genius guys". Leonard also shows her his whiteboard which Sheldon says should not impress her. Penny is introduced to Sheldon's obsessiveness when she accidentally sits in Sheldon's spot on the couch. Sheldon gives his first rendition of how that spot is perfect based upon the temperature, air currents and television visibility. She is also told that they like to play their game of Klingon Boggle.

Penny begins her story that she is a Sagittarius that tells them a lot about her. Sheldon concludes that she participate in the mass cultural delusion that the sun's apparent position relative to arbitrarily defined constellations and the time of your birth somehow affects your personality. She is a vegetarian except for fish and an occasional steak, which she loves. Also is from Nebraska, worked at the Cheesecake Factory, and is writing a screenplay about a sensitive girl who moves from Nebraska to be an actress. She also fell in love with a jerk that she has been living with for four years. Even though he lied and cheated, she still loves him and breaks into tears which the guys don't know what to do about. Leonard describes her dilemma as a paradox using as example the physics understanding of the light simultaneously as a wave or a particle (although, as postulated that the Bohr's principle of complementarity, only one of natures can be detected each time). Penny doesn't really understand, but then she mentions that she feels so dirty and gross and her shower doesn't work. Leonard offer her to use their shower.

Periodic Table Towel

Penny's towel. She's naked in there.

As she is taking a shower, Howard and Raj arrive with a video of Stephen Hawking from 1974, which excites them because it was before the time that he uses a computerized voice simulator. Howard says that phrase while doing his famous Stephen Hawking impersonation. Penny exits the shower only wearing a towel because she can't get the water to go from tub to shower, and she is introduced to them. Howard, thinking he is a professional ladies' man, hits on Penny while Raj is rendered silent since he can't speak in front of women due to his selective mutism, which was unknown at the time.


Can you speak English?

Leonard returns with her to the bathroom and gets the shower to work. She then steps into the shower and throws the towel over the curtain to an amazed Leonard. Penny then asks Leonard a favor, asking him to pick up her television from her ex-boyfriend, Kurt who lives across town. Due to his crush on Penny, Leonard agrees and drags Sheldon along. During their ride to Kurt's apartment, we discover that Leonard's last girlfriend was a North Korean spy named Joyce Kim.

Kurt in pilot

Sheldon and Leonard meet Kurt.

Upon their arrival, they are denied access to the building, but by observing two clever girl scout types get into the building, they quickly slip in behind them. Penny's ex-boyfriend, who turns out to be a tall and very muscular man, refuses to give up the TV, and apparently finds Leonard and Sheldon so irritating that for that he robs them of their pants.



They return to their apartment, pants-less and TV-less. Penny feels sorry for Leonard and Sheldon after their incident and decides to make it up to them by paying for their dinner (along with Howard and Raj). While looking at Penny's apartment Sheldon tells Leonard that this thing with Penny isn't over. Leonard tells him that their children will be both smart and beautiful, to which Sheldon adds, "Not to mention imaginary."

Pilot - Penny, Leonard, Howard, Raj, and Sheldon in car

The 5 friends in the car near the end of the episode.

In the car, the episode ends with Sheldon telling Leonard that despite the low chances of him starting a relationship with Penny, in comparison to the other males in the car; he is a "veritable Mac Daddy".



Vanity Card 182

Chuck Lorre Productions, #182, the vanity card shown at the end of the Pilot.

  • The TV Critic: "Penny is a brave new world for Sheldon and Leonard and it’s a fun start to The Big Bang Theory. The show will have to work hard to maintain the delicate balance between geek jokes and real characters. I wish them luck."[1]
  • Scott Tobias of the AV Club, gave the episode a D+[2]
  • IMDB user reviews


  • Title reference: Only episode that had no individual title.
  • This episode was not the first pilot. The first one was unaired because it was not approved.
  • The name of the High-IQ sperm bank receptionist its never said on screen, although the name "Althea" its written on her tag and its present in the credits.
  • This episode was watched by 9.52 million people with a rating of 3.7 (adults 18–49).[3]
  • Chuck Lorre's vanity card.
  • Episode Transcript

The Earlier "Final Sales Version"

There is a "Final Sales Version" of the "Pilot" which predates the generally known broadcast version. The date displayed in the sales version is March 21, 2007. The two versions are largely the same. Most of the scenes in the earlier version have been preserved in the later aired version, except the following two:

  1. The opening scene in the sperm bank: This scene in the sales version is somewhat between the one in the aired version and the one in the "Unaired Pilot". In the sales version scene, both Leonard and Sheldon have made their sperm deposits like in the "Unaired Pilot" scene. But Sheldon thinks they are committing fraud, so he really changes his mind and asks the receptionist Althea for his sperm back. Therefore, the two do not sell their sperm in the end, a bit similar to the scene in the aired "Pilot". The scene in the aired version is a reshoot, evidenced by Althea's longer hair. They all wear the same clothes for the reshoot so that it will match the later scenes in the guys' apartment.
  2. The scene of Leonard driving to see Kurt with Sheldon: The one in the aired version is again a reshoot and slightly longer than the sales one. And the main difference is that Leonard's ex-girlfriend Joyce Kim and her defection to North Korea is only mentioned in the later aired version.

Other differences include:

  • The name of the show and some other information are displayed in text at the start of the sales version.
  • The sales version has no opening and closing credits, vanity card and company logo.
  • The sales version does not have a theme song. Instead, it displays the title "The Big Bang Theory" with an animation of an atom on a yellow background. Two similar animations of an atom without the show title are used between scenes as well.

Costume Notes


Capsaicin t-shirt


Flashy Safari


Converse shoes

The Euclid Alternative 12 - Nintindo

Nintendo buckle

Leonard is sporting a t-shirt featuring the capsaicin molecule (the stuff that makes chili peppers hot, makes pepper spray a great defense agent, and, ironically, has pain-relieving and numbing qualities). He wears Jack Parcell shoes.

Sheldon's t-shirt is the "DC Flashy" shirt, on safari brown.

The pilot also exposes Raj's penchant for bad sweater vests, and Howard's love of alien pins (almost always worn on the collar of his dickey or turtleneck) and his unique belt buckle collection, this episode featuring one in the design of a vintage Nintendo controller.

In her debut, Penny is wearing classic Ugg boots.


  • This episode and the unaired pilot are the only ones to be filmed on 35-mm film. Everything after that was shot on digital video.
  • When aired in syndication, the sperm bank scene is not shown, likely because it contrasts with the nearly asexual Sheldon that would be established in later seasons' episodes.
  • Penny is forced to do a favor for Leonard in "The Killer Robot Instability" (S2E12) after he loses his pants to Kurt.
  • Sheldon wears briefs and Leonard wears boxers.
  • Sheldon reveals that he has 212 friends on MySpace.
  • Sheldon has the first line in the series.
  • Sheldon has the last line in the episode (except for Howard, who is still singing).
  • There were 6 magazines on the table in the high-IQ sperm bank.
  • In this episode, Leonard states that the combined IQ of Sheldon and himself is 360. (Sheldon's IQ is mentioned in “The Pancake Batter Anomaly” (S1E11) to be 187, making Leonard's 173.)

Leonard drinks a bottled orange soda.

  • In this episode, Sheldon and Leonard are seen drinking bottled orange sodas, which sparked controversy over whether it was beer or not, due to Sheldon's incredibly low alcohol tolerance.
  • When the guys first notice Penny, her boombox is playing the song "Smile" by Lily Allen.
  • The scene where Sheldon and Leonard observe Penny through her open apartment door would be repeated as an homage in the series' 100th episode, Season 5's "The Recombination Hypothesis" (S5E13). The characters would even be dressed similarly, right down to Penny wearing the exact same blue top that she wears here.
  • Penny's clothes change after her shower, but she didn't have another set with her and it appears she didn't return to her apartment since Raj and Howard were there.
    • It's possible that one of the guys got her a change of clothes from her apartment as a favor.
  • Sheldon refers to a window in the kitchen, which is there, but is usually obscured by a whiteboard. This statement implies apartment 4A is along a corner of the building.
  • Darth Vader Shampoo and Luke Skywalker Shampoo actually exist, but there isn't a conditioner, so it's likely Leonard reuses Darth Vader as shampoo and Luke Skywalker as a conditioner.
  • While Penny has a pleasant outgoing personality, Katie from the unaired pilot opening was meaner and mocked them. Penny does have a temper and some of these personality traits came over from the woman in the first pilot when Penny is really mad.
  • The family names of Howard (Wolowitz) and Rajesh (Koothrappali) were revealed in this episode, while Sheldon's (Cooper) and Leonard's (Hofstadter) were not.
  • The experiment discussed by Sheldon at the very beginning of the episode is a quantum version of the well-known "double-slit experiment." Sheldon thinks this would be a good idea for a t-shirt and, ironically, such an observed photon t-shirt now exists.
  • The only episode where Raj was seen with a baseball cap.
  • When Penny left after Howard suggested that she should have her own game character, Raj was seen talking for a brief moment in the same room with Penny saying "smooth" to Howard. This makes it the first time Raj has been seen talking in the same room with Penny.
  • The song that Howard sings to Penny at the end is "Don't Get Hooked on Me" by Mac Davis.
  • The Pilot was rewritten and filmed twice.
  • Even though Leonard thinks that his and Penny's offspring will be smart and beautiful, genetically they could also be dumb and plain. 
  • In "The Focus Attenuation" (S8E5), Sheldon verified that Penny moved in 9/24/2007, the date of the premiere of the series pilot.
  • Penny asks Sheldon if he is one of those 'Beautiful Mind' geniuses. Her actress Kaley Cuoco appeared alongside 'Beautiful Mind' star Russell Crowe in the film 'Virtuosity'.
  • In a later episode, Sheldon tells Penny that Howard had found her movie "Serial-Apist" online right after they had met her, the minute she had walked out the door. This means that they saw it between this episode and "The Big Bran Hypothesis" (S1E2).
  • The episode mentions Sheldon's twin sister Missy who works as a hostess at Fuddruckers and appears in the next 14 episodes ("The Porkchop Indeterminacy") and is heard screaming in the eleventh episode of Season 7 ("The Cooper Extraction").
  • Leonard mentions that his grandmother was there for Thanksgiving, had Alzheimer's and got naked. Later it is established that he was from New Jersey making his ill grandmother traveling all the way across the country implausible unless she happened to live in California
  • In the pilot promo that shows all the computer companies and why nerds are taking over and why you have to be nice to them. The Big Bang Theory - Official Trailer (HD) - YouTube



Unaired Pilot

Quantum Mechanics with a little String Theory doodling around the edges. Unaired pilot.

  • Sheldon: Yeah, well, it’s just some quantum mechanics with a little string theory doodling around the edges. That part there's just a joke. It's a spoof of the Born-Oppenheimer approximation.
Top Quark Decay

Top quark decay.

    • Sheldon's dialogue is incompatible with the work presented on the whiteboard. This one (left) describes the decay of the top quark. For more detail, see the blog here.
    • Sheldon's dialogue was meant to accompany the whiteboard seen in the Unaired Pilot (right).


Sheldon: So if a photon is directed through a plane with two slits in it and either slit is observed, it will not go through both slits. If it’s unobserved, it will. However, if it’s observed after it’s left the plane, but before it hits its target, it will not have gone through both slits.
Leonard: Agreed, what’s your point?
Sheldon: There’s no point, I just think it’s a good idea for a T-shirt.
Leonard: Excuse me?
Receptionist: Hang on.
Leonard: One across is Aegean, eight down is Nabakov, twenty-six across is MCM, fourteen down is… move your finger… phylum, which makes fourteen across Port-au-Prince. See, Papa Doc’s capital idea, that’s Port-au-Prince. Haiti.

(Leonard and Sheldon are going upstairs to their apartment after an unsuccessful visit to the "High IQ" sperm bank. They have to use the stairs since the elevator has been broken for at least four years.)
Sheldon: Are you still mad about the sperm bank?
Leonard: No.
Sheldon: You wanna hear an interesting thing about stairs?
Leonard: Not really.
Sheldon: If the height of a single step is off as little as 2 millimeters, most people will trip.
Leonard: I don't care... 2 millimeters? That doesn't seem right.
Sheldon: No, it's true, I did a series of experiments when I was 12; my father broke his clavicle.
Leonard: Is that why they sent you to boarding school?
Sheldon: No, that was a result of my work with lasers.
(The guys are about to go in their apartment, but they soon realize there is a new neighbor across the hall who has just moved in. She is a young and attractive blonde woman and is reading a magazine.)
Leonard: New neighbor?
Sheldon: Evidently.
Leonard: Significant improvement over the old neighbor.
Sheldon: 200-pound transvestite with a skin condition? Yes, she is.
(The woman notices the guys.)
Woman: Oh, hi.
Leonard: Hi.
Sheldon: Hi.
Leonard: Hi.
Sheldon: Hi.
Woman: Hi?
Leonard: We don't mean to interrupt, we live across the hall.
Woman: Oh, that's nice.
Leonard: Oh, w..., a..., w..., we don't live together, we..... We live together, but in, separate, heterosexual bedrooms.
Woman: Oh, OK, guess I'm your new neighbor. Penny.
Leonard: Uh, Leonard, Sheldon.
Penny: Hi.
Leonard: Hi.
Sheldon: Hi.
Penny: Hi.
Leonard: Hi.
(There is a short silence.)
Leonard: Well, uh, oh, welcome to the building.
Penny: Thank you, maybe we can have coffee sometime.
Leonard: Oh, great.
Penny: Great.
Sheldon: Great.
Leonard: Great (silence). Well, uh, bye.
Penny: Bye.
Sheldon: Bye.
Leonard: Bye.
(Penny closes her door.)

(The guys have decided to invite Penny over for lunch.)
Penny: So, what do you guys do for fun around here?
Sheldon: Well, today we tried masturbating for money.

(Penny gets her first look at Sheldon's work on his white board.)
Penny: This looks like some serious stuff, Leonard, did you do this?
Sheldon: Actually, that's my work.
Penny: Wow.
Sheldon: Yeah, well, it’s just some quantum mechanics, with a little string theory doodling around the edges. That part there, that’s just a joke. It’s a spoof of the Bourne-Oppenheimer approximation.
Penny: So you’re like, one of those, beautiful mind genius guys.
Sheldon: Yeah.

Howard: Wait till you see this.
Raj: It's fantastic. Unbelievable.
Leonard: See what?
Howard: It's a Stephen Hawking lecture M.I.T. in 1974.
Leonard: This isn't a good time.
Howard: (imitating Stephen Hawking) It's before he became a creepy computer voice.

(After Penny has just met Howard and Raj, she slumps down on the couch next to Rajesh.)
Penny: (to Raj): So, you guys work with Leonard and Sheldon at the university?
(Raj doesn't answer and just continues to eat his food.)
Penny: I'm sorry? Do you speak English?
Howard: Oh, he speaks English; he just can't speak to women.
Penny: Really? Why?
Howard: He's kind of a nerd. (starts talking smooth) Juice Box?

(Leonard and Sheldon are about to get Penny's T.V. from her ex-boyfriend, Kurt. They're about to talk to the intercom.)
Leonard (To Sheldon): Now let me do the talking.
Kurt (via intercom): Yeah.
Leonard: (via intercom): Hi, I'm Leonard and this is Sheldon.
Sheldon (To the intercom.): Hello.
Leonard (To Sheldon muttering a few random words): Ah! Uh, just... (To Kurt via intercom) We're here to pick up Penny's T.V.
Kurt (via intercom): Get lost.
Sheldon (To Kurt via intercom.): OK, well, thanks for your time.

(After being refused entry into the building by Kurt, Sheldon and Leonard manage to get into the building after some girl scouts selling cookies enter and the guys sneak in after them before the door closes. They then arrive at Kurt's door. When the two see what Kurt looks like (a big, strong, and tough guy), they get nervous.)
Kurt: Yeah.
Leonard: Hi. I'm Leonard and that's Sheldon.
Sheldon: From the intercom.


Kurt: How the hell did you get in the building?
(Leonard is frightened and lost for words)
Leonard: Uh...we're scientists.
(Kurt is just staring at him, Sheldon whispers to Leonard)
Sheldon: Tell him about our IQ.
(A short time later, Leonard and Sheldon come out the building robbed of their pants.)
Sheldon: Leonard.
Leonard: Yes?
Sheldon: My mom bought me those pants.
Leonard: I'm sorry.
Sheldon: You're gonna have to call her.

Raj: Smooth.

Penny: (after seeing Leonard and Sheldon pantsed): I'm so sorry. I really thought if you guys went instead of me, he wouldn't be such an ass.
Leonard: No, it was a valid hypothesis.
Sheldon: That, was a valid hypo--what is happening to you?

Sheldon: You're not done with her, are you?
Leonard: Our babies will be smart and beautiful.
Sheldon: Not to mention imaginary.

Sheldon: I don't know what your odds are in the world as a whole, but as far as the population of this car goes, you're a veritable Mac Daddy.



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