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"The Large Hadron Collision" is the fifteenth episode of the third season of the American sitcom The Big Bang Theory. The episode first aired on Monday, February 8, 2010.


Leonard is going to Switzerland to observe the Large Hadron Collider and is planning to take Penny for a romantic Valentine's Day experience, but Sheldon has other ideas about who should be going with him.

Extended Plot[]

It's nearly Valentine's Day, and Howard is excited to announce his plans since he has a girlfriend. Sheldon wonders why Howard would celebrates a 3rd-century saint who was stoned and beheaded. That still beats Raj who is spending his night with a rotisserie chicken. Leonard is going to Switzerland to observe the Large Hadron Collider at the CERN Laboratory and taking Penny as his “Plus One”. Sheldon is beyond ecstatic, so much so that he didn't bother questioning why Leonard would get such an honor. Sheldon is assuming that Leonard will take him since Penny has no interest in subatomic particle research while Leonard has been dreaming of spending Valentine's Day with a girl since he was 6.


Guessing game with Penny.

Leonard has assembled for Penny clues on where they're going, but apparently the Swiss Cheese cut by the Swiss Army Knife and the fondue set aren't enough. She is not excited about the CERN Lab Super Collider in Switzerland, but she is excited about going to ski in Switzerland. And then Sheldon whips out their Roommate agreement. There is a clause stating one roommate must take the other if one of them gets invited to the CERN Supercollider. It doesn't contain any clauses about girlfriends because that seemed too far-fetched when the contract was signed.

Sheldon has lived up to his part of the roommate agreement including asking how Leonard is doing at least once a day, not staging mock biohazard drills after 10 P.M. and not practicing Tuvan throat singing which he demonstrates. To Sheldon, Leonard is a bigger traitor than Judas, who did hang himself, Darth Vader, Benedict Arnold, and Rupert Murdoch, who owns Fox network, the network that canceled "Firefly."

In the morning, Sheldon makes Frodo-shaped pancakes and serves Leonard in bed and suggesting they watch "Babylon 5" with director's commentary, even though he hates it. Leonard doesn't change his mind so Sheldon takes the pancakes away.

Sheldon then approaches Penny. In the laundry room, Penny is shown a PowerPoint presentation for her about why he is the more appropriate choice to go. He has images of himself and Penny, and of the Super Collider and Bath & Body Works. She has to match the person to where they should be. Penny tells him that it's Leonard's decision and he chose her. Sheldon walks away telling her that it's his dream to go and then she says she'll talk to Leonard. Sheldon thanks her, and even hugs her while asking her when to stop.

Leonard is angry that he went to Penny behind his back and says Sheldon isn't going, even admitting if Penny didn't exist, he'd go alone rather than take him. Thus ends the "friendship clause" in their roommate agreement and Sheldon will never take Leonard as his guest when Bill Gates invites him to go swimming.

The morning they are leaving, Penny catches the flu. Now Sheldon can go, and he'll pack as soon as he's done vomiting.


Penny and Sheldon sick together.

Sheldon is perplexed on how he got the flu...until he remembered he hugged Penny. She made him sick and they end up taking care of each other spending Valentine's Day together. 

In Switzerland, Leonard and Raj get a beautiful room. The chocolates and the champagne Leonard bought for Penny make the day for Raj the best Valentine's Day ever!



  • "Sheldon has his moments including a witty retort to Penny calling him an alien: “Extraordinary intelligence might well appear extra-terrestrial to you..." The conclusion of the plot had a kind of justice to it with Raj getting a good Valentine's Day for once and Sheldon not being rewarded for his bad behavior...The plot could have focused on Penny and Leonard's relationship and how they were going to cope on their first holiday together. But no, instead we got Sheldon trying to enforce rules, to butter Leonard up and then to convince Penny not to go in to the room...Sheldon is unlikable all the time but he is funny. Leonard comes across as an irritable coward most of the time which isn't likable. I believe the whole show would benefit from addressing these character flaws. Otherwise we will get more episodes like this where there is no one to like." - The TV Critic's Review
  • IMDb user reviews


  • Title Reference: The dispute between Leonard and Sheldon over who gets to be Leonard's guest for the trip to the Large Hadron Collider.
  • Chuck Lorre's vanity card [1]
  • This episode was watched by 16.26 million people with a rating of 6.0 (adults 18-49).
  • This episode aired in Canada on February 8, 2010 with 2.05 million viewers and a weekly ranking of #15.
  • Episode transcript [2]

Costume Notes[]

Aquaman II Astrosmash Purple crew neck


  • There are no more guest appearances by Melissa Rauch as Bernadette until she starts to be featured as a main cast member in "The Hot Troll Deviation" of Season 4 in The Big Bang Theory. The first of nine Season 3 episodes where she doesn't get featured in as a guest star anymore.
  • After Leonard informs his roommate he would not be joining him in Switzerland, Sheldon explains, "I’ve been dreaming about going to the Large Hadron Collider since I was nine years old". Although the LHC was not under construction at that time (ca. 1989), technical planning for the high-energy particle accelerator had already begun.

    Another rare hug from Sheldon.

  • While the 3.8-meter (12 ft) wide concrete-lined tunnel containing the collider was constructed between 1983 and 1988, it was formerly used to house the Large Electron–Positron (LEP) collider. Back in the early 1980s, when the Large Electron-Positron collider was being designed and built, groups at CERN were already busy looking at the long-term future. After many years of work on the technical aspects and physics requirements of such a machine, their dreams came to fruition in December 1994 when CERN's governing body, the CERN Council, voted to approve the construction of the LHC. Between 1996 and 1998, four experiments—ALICE, ATLAS, CMS and LHCb—received official approval and construction work commenced on the four sites. The Large Hadron Collider was built by the European Organization for Nuclear Research (CERN) from 1998 to 2008 and went live for the first time on 10 September 2008.
  • Sheldon believes Leonard's betrayal is worse than Judas Iscariot for the heinousness of his betrayal, an allusion to Sheldon's religious upbringing. On the other hand, Sheldon says Judas had the decency to hang himself after what he did. As Judas was paid with 30 pieces of silver, Sheldon slaps down a tray with 30 pieces of silverware in front of Leonard.
  • Leonard mentions "one giant marble horse," in reference to Howard and Bernadette going to P. F. Chang's China Bistro. P.F. Chang's was also linked to Howard's mom as well as a double date for Howard and Bernadette and Leonard and Penny in the previous isode.
  • Sheldon gives out one of his rare hugs for Penny. He later blames his illness on the physical contact associated with the hug, and not knowing she may have had the flu at that time.
  • In the commitments under the Roommate Agreement, Leonard can't kill Sheldon if he turns into a zombie, but there is a reciprocity clause; that is, he gets to pull the plug on him, as revealed "The Roommate Transmogrification".
  • When Sheldon quotes the Roommate Agreement, Penny asks, "Is there anything in there about if one of you gets a girlfriend?" Sheldon replies, "No, that seemed a little farfetched"; however, in "The Vartabedian Conundrum" (S2E10), after Leonard begins to live together with Stephanie Barnett, Sheldon immediately quotes terms about girlfriends from the Roommate Agreement. He may have most likely referred to the clauses regarding the Hadron Collider trip in this episode.
  • The song Sheldon plays to Leonard on his recorder is "Morning", composed by Edvard Grieg for the play Peer Gynt.
  • Bernadette is mentioned one time by each guy (Leonard and Howard) in each cafeteria scene during this episode, but she is not seen with an actual appearance in any of the scenes in this episode.
  • Marcus Folmar thrice played a guard/policeman on The Big Bang Theory.
  • After learning that Leonard was going to Switzerland, Sheldon immediately took off to start packing at home; however, it's not clear how he got home, given that he needed someone to drive him. It could be that he took the bus.
  • The first of many Valentine's Day episodes.
  • This is the second episode where Sheldon hugs Penny; the first was in "The Bath Item Gift Hypothesis".
  • An easier solution would have been to take both Sheldon and Penny. Sheldon could have merely purchased his own plane tickets and hotel reservation and given that Penny has no interest in the Super Collider just taken Sheldon to that particular aspect.


  • In this episode, Sheldon states that there is nothing in The Roommate Agreement about girlfriends, as it seemed unfathomable. This contradicts a statement made in "The Vartabedian Conundrum" (S2E10) about parameters which deem a girlfriend to be "living with them".
    • This might be in relation to this specific clause.


Sheldon: Alright, this game is called Traitors. I will name three historical figures and you will name them in order of the heinousness of their betrayal. Benedict Arnold, Judas, Dr. Leonard Hofstadter.

Sheldon: Given that Saint Valentine was a third century Roman priest who was stoned and beheaded, wouldn’t a more appropriate celebration of the evening be taking one’s steady gal to witness a brutal murder?

Penny: Okay, what’s the big surprise?
Leonard: Just a minute. This tray contains clues as to what you and I are going to be doing on Valentine’s Day.
Penny: Oh. Wow. Okay. Let’s see. We’ve got, uh, milk chocolate, Swiss cheese, fondue. My lactose-intolerant boyfriend is going to eat all this; then I’m going to climb on his back and rocket to the moon?
Leonard: No. But it does involve air travel. Okay, um, let me slice this Swiss cheese with my Swiss army knife, and then you can wash it down with a cup of Swiss Miss instant cocoa.
Penny: Okay, I’m starting to think Swiss is key here.
Leonard: Uh-huh.
Penny: We’re going to Disneyland and ride the Matterhorn?
Leonard: How does that involve air travel?
Penny: We’re going to Disney World and ride the Matterhorn?
Leonard: No.
Penny: Okay, sweetie, this started out fun, but I’m over it.
Leonard: We’re going to Switzerland to see the CERN supercollider! And ski. We’ll also go skiing.
Penny: We’re going skiing in Switzerland?!
Leonard: Well, you’ll ski, I’ll fall, but, yeah, we will be in Switzerland for Valentine’s Day.
Penny: Oh, my God, Leonard! That’s incredible!

Sheldon: Since I rarely hug, I am relying on your expertise regarding duration.
Penny: I think we're there.

Sheldon: It's you. I touched you!
Penny: Happy Valentine's day.