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"The Hofstadter Isotope" is the twentieth episode of the second season of the American sitcom The Big Bang Theory. This episode first aired on Monday, April 13, 2009.


Penny needs a present for her nephew's birthday, so she accompanies the guys to the comic book store. There she meets the owner, Stuart, who manages to ask her out on a date. Feeling jealous about the situation, Leonard demands that Howard and Raj "take (him) to a bar with women."

Extended Plot[]

During Anything Can Happen Thursday, Sheldon suggests they go to the the comic book store even though they only went to it yesterday, prompting Howard to suggest going to a bar to meet hot women. Leonard and Raj decide it's a good idea, but go in favor of finishing their Thai food and then going to the comic book store.

The Hofstadter Isotope 11

In the hallway.

As the boys are leaving for the comic book store, Penny runs into them and asks if they can pick up a few comic books for her nephew's birthday. After much pestering by Sheldon, Penny goes with them. Once at the comic book store, Penny meets Stuart, the guy who owns the store, and a good friend of the guys'. Meanwhile, Sheldon and Howard get into a fight over a comic book (All-Star Batman and Robin the Boy Wonder #8 variant), (Sheldon needing it for his Robin collection and Howard needing it for his Batman collection). After Howard is distracted by Penny talking to Stuart, Sheldon wins and gets the comic book. Penny agrees to go out with Stuart as long as Stuart gives Penny the sketch he just drew of her.


Stuart's sketch of Penny.

The following night, Leonard sees Stuart and Penny leaving for Stuart's opening at a local gallery and immediately becomes jealous, while they are about to embark on "Friday night the way it was meant to be" featuring the buggy beta version of Zork (much to Sheldon's pleasure). Leonard tells Howard to take him to a bar to meet women.

The Hofstadter Isotope 14

Raj and his friend.

Once they arrive at the bar, Raj annoys Howard by ordering drinks that Howard considers unmanly, including a Chocolate Martini, a Brandy Alexander, and his signature Grasshopper. Howard leaves Raj at the bar, and he and Leonard strike out by themselves. Leonard quickly learns that Howard isn't the ladies' man he claims he is. He insists on letting the "important men" (lawyers, jocks, etc.) thin the herd so they can pick at whoever is left. He also tries to pick up women with silly party gags, instead of just talking to them. Not surprisingly, no women want to talk to them. When Leonard questions Howard about it, Howard states that Leonard is weighing him down. Leonard doesn't believe it. Howard decides they should give up and go, when they spot Raj making out with an overweight woman. Both are stunned, and Howard is especially baffled, unable to understand how Raj got a woman and he couldn't.

Meanwhile, as Stuart and Penny return to her apartment for a cup of coffee. Stuart thinks that a "cup of coffee" means the beverage and not making out together. Sheldon runs into them in the hallway. Sheldon and Stuart get into a slightly heated debate over rather Dick Grayson or Jason Todd would be Batman II if the original Batman's death proved permanent. Sheldon declares himself the winner after Stuart gets tired and they find Penny has fallen asleep on the couch.

Finally, Raj wakes up in the bed of the woman he was making out with at the bar the previous night looking very pleased with himself.




  • Title reference: Leonard claims that Stuart is essentially the same person as he is.
  • Chuck Lorre's vanity card [1]
  • This episode was watched by 10.13 million people with a rating of 3.9 (adults 18–49).
  • Episode transcript [2]

Costume Notes[]

The Hofstadter Isotope 18

Flash Lightning

The Hofstadter Isotope 17

AV Club

The Hofstadter Isotope 19


The Hofstadter Isotope 21

Red Cassettes

Sheldon wears a blue Flash Lightning shirt by CTRL; it's been discontinued and the closest I've found is a knockoff at Next the AV Club shirt by Heavy Rotation. Leonard wears a green shirt with green amorphous shapes and the red cassette tapes shirt, originally sold at Target, now a knock off from CafePress.

Set/Props Notes[]

The Hofstadter Isotope 20

All-Star Batman & Robin #8 Variant A

At the comic store, Sheldon and Howard argue over a comic they both want for their collections. The comic is All-Star Batman and Robin, Issue #8, from January 2008. The issue they hold in the episode is actually a "variant" (Variant A, to be exact, there were several for this issue), an alternative cover to the one published in the regular run of the issue. Mint copies of this baby run over $100. Reading copies can be had for under $20. 


  • First appearance of Stuart Bloom in the series. He is much more normal initially then he would go on to be.
  • Howard says his name is Sanjay Wolowitz, possibly based on Raj's cousin who is named Sanjay.
  • Howard's calculations of potential women that they could pick up is based on the Drake Equation, which attempts to calculate odds of finding intelligent alien life in the Milky Way galaxy. Dr. Frank Drake came up with an equation to examine factors of: the rate of star formation (R), the number of stars with planets(fp), the number of planets per solar system suitable for life(ne), the number of those with ACTUAL life(fl), the number of those with INTELLIGENT life(fi), the number of those whose activities emit detectable signs of their life into space where we could find it (fc), and the length of time that those signals are emitted (L).
    • Thus:
  • Howard's modified version of Drake's Equation to calculate the chances of them having sex is based on the number of single women in LA (sw_LA), the number of those who might find them attractive (fa) and the Wolowitz Coefficient (W), where W is neediness (n) times dress size (ds) squared.
    • Thus: , where
    • All combined:
  • This episode marks the first appearance of Stuart Bloom, who would go on to become a recurring character and later main character. He was also a tool to help advance the Lenny and Shamy couples when he went out with each of the girls.
  • Stuart and Sheldon argue over who would succeed Bruce Wayne as Batman. Though, they might both be wrong in terms of the Robins, as Dick Grayson became Nightwing while Jason Todd was "killed off" before returning as Red Hood.
  • First episode where the scene transition wipes of atoms also appear at the beginning of the episode. It stays for the rest of the series, only absent in the next episode. 
  • Sheldon refers to the Star Trek DS9/Original Series crossover as "The Trouble with Tribbles" while talking to Leonard on the couch. This was the title of the original 1967 episode, but the amalgam into which DS9 elements were woven in 1996 was "Trials and Tribbl-ations."


Howard: Yeah, that one. You can modify it to calculate our chances of having sex by changing the formula to use the number of single women in Los Angeles, the number of those who might find us attractive, and what I call the Wolowitz Coefficient.
Raj: The Wolowitz Coefficient?
Howard: Neediness times dress size squared. Crunching the numbers, I come up with a conservative 5,812 potential sex partners within a 40-mile radius.

Sheldon: Well, I’ve spent the last three hours in an online debate in the DC Comics Batman chat room, and I need your help.
Stuart: Oh yeah. Those guys can be very stubborn. What’s the topic?
Sheldon: I am asserting, in the event that Batman’s death proves permanent, that original Robin, Dick Grayson, is the logical successor to the Bat Cowl.
Stuart: Ooh, Sheldon, I’m afraid you couldn’t be more wrong.
Sheldon: More wrong? Wrong is an absolute state and not subject to gradation.
Stuart: Of course it is. It’s a little wrong to say a tomato is a vegetable, it’s very wrong to say it’s a suspension bridge. But returning to the original issue, Dick Grayson became Nightwing, a superhero in his own right. Batman 2 has to be the second Robin, Jason Todd.
Sheldon: Has to be? Has to be? I hope you’re being deliberately provocative

Penny: Hi. What would you recommend as a present for a 13-year-old boy?
Stuart: A 13-year-old girl. But if you’re dead set on a comic book, try this.
Penny: Oh, Hellblazer. What’s this about?
Stuart: A morally ambiguous confidence man who smokes, has lung cancer and is tormented by the spirits of the undead.
Penny: Well, if that doesn’t make me the favorite aunt, I don’t know what will. (sees Stuart's drawing) Is this me?
Stuart: Depends. Do you like it?
Penny: It's really good.
Stuart: Yes, that's you.
Penny: That's so sweet. But what if I didn't like it?
Stuart: It'd still be you, but I'd feel like an idiot.