"The 43 Peculiarity" is the eighth episode of the sixth season of the American sitcom The Big Bang Theory. This episode first aired on Thursday, November 15, 2012.
In this episode, Sheldon has a daily 20-minute time period between 2:45 and 3:05, where Howard and Raj determine to find out what he is doing. Meanwhile, Leonard is jealous over Penny's (male) college class partner.
Sheldon mentions one day in the cafeteria that he could, in theory, build a containment field to open a wormhole to another dimension the size of a Frisbee. When Sheldon leaves, he hands the napkin, on which he has been doodling some thought on a wormhole generator, to Howard. Howard wants to know if he wants to build it. Sheldon says that he wants him to wipe his chin; he has food on it. After Sheldon leaves, Howard notices that Sheldon's pristine schedule has a lapse of 20 minutes every afternoon where no one knows where he goes or what he does. Raj guesses that he heads to the men's room, while Leonard corrects him since that is not on Sheldon’s pristine schedule. Raj and Howard corner him in the hallway by his office, and Sheldon denies that anything is unusual. They then ask his assistant Alex, and she reveals that even she doesn't know where he goes.
Later, Penny and Leonard are hanging out in her apartment. Penny is texting a fellow English student named Cole, who's working with her on an oral class project. Jealous, Leonard asks if he and Penny are still dating and is convinced that Cole is flirting with Penny, but Penny denies it and says that he's just being nice. Leonard begins chatting with Alex in the Cafeteria about it, and she mentions that it is probably nothing. She then coyly adds that Leonard might even be flirted with without really knowing it. He the walks out with his coffee laughing hysterically while Alex looks disappointed. Elsewhere at Caltech, Raj and Howard follow Sheldon down to an old storage room in the basement. Unable to hear what he's doing, Howard and Raj break in later that night and find an almost empty room with a blackboard that has the number 43 written on it. Given Sheldon's apparent obsession with order and numbers, Raj and Howard spend all night trying to figure out what the significance of the number 43 is. Howard's mom has 43 inches of neck fat.
Later, when Cole comes over to Penny's to work on the project, Leonard spies on him from his apartment. Leonard follows him down the stairs and tells him to watch out for "Penny's boyfriend", saying that he was a gang member. When Cole says that Penny told him that her boyfriend was a scientist, Leonard makes the excuse that "The Scientists" was the name of his gang. Penny witnessed his stunt and is upset with Leonard and the two later meet in the hallway and have an argument. Penny tells him that she cannot believe that he cannot trust her and that he embarrassed her in front of Cole who knew who he was since his picture is on her refrigerator. Penny continues to tell him that he is the one she is with and accidentally mentions that he knows that she loves him. Leonard is stunned and tells her that that is the first she ever said that. Penny rushes off to work to avoid crying in front of him. Leonard gets a text from Alex, inviting him for coffee sometime, and Leonard smiles, mentioning that she is such a friendly girl.
Unable to solve what 43 means, Howard installs a spare camera from the Mars rover project so they can spy on Sheldon in the storage room. The next day, Howard and Raj watch the video feed, and are stunned when they see Sheldon use an unknown machine to create a small wormhole in the room. Sheldon mentions aloud into a recorder that he hasn't found life in 43 parallel universes, and thrusts his head through the wormhole. Sheldon backs out, screaming as a reptilian creature eats his face. The creature is suddenly dropped on their laptop from behind them, it was Sheldon. He had found the camera and created a phony video to cover up what he was really doing. Sheldon reprimands Howard and Raj for their nosy businesses and explains that what he did with his spare time was none of their business, but was centered around giving his mind a break from his struggles with understanding social behavior and the mental bombardment caused by his work. He then leaves telling them that they'll never know.
Later, Sheldon is seen in the storeroom playing with a Hacky Sack, telling himself that he'll never reach 43 consecutive hits again.