The Lunar Excitation

"The Lunar Excitation" is the twenty-third episode and the final episode of the third season of the  sitcom The Big Bang Theory. This episode first aired on May 24, 2010.

Summary
The gang meets Penny's dim-witted new guy Zack while performing a experiment on the apartment building roof. Raj and Howard sign up Sheldon for online dating and find him a match.

Extended Plot
The guys set up an experiment on the building's roof to bounce a laser off the moon and back to Earth using the laser reflector left by the crew of. Leonard thinks Penny might enjoy that, so he goes to get her only to find she has male company. Zack Johnson, Penny' date, wants to see the experiment and Penny joins them. Zack demonstrates himself to be extraordinarily dim witted thinking that they might blow up the moon. The guys fire the laser and get a return 2.6 seconds later successfully hitting their target. Leonard explains they proved that there are man-made objects left on the moon by a species that only 65 years before learned to fly. Zack wants to know what species that was. Later that night Penny gets drunk, bangs on Leonard's door waking him up and berates him because he has ruined her ability to date stupid men. She then has a one night stand with Leonard, but realizes it was a mistake the next morning. Leonard gets the idea that he can walk up to women and have casual sex with them with it meaning nothing. So he goes to ask Leslie Winkle to do the same, but gets turned down. After getting drunk, Leonard visits Penny's apartment telling her that she ruined him and asks to sleep with her, which she quickly turns him away leaving Leonard confused.

Meanwhile, Howard and Raj submit an site profile for Sheldon that surprisingly results a match. Sheldon believes dating sites to be "hokum" and refuses to meet the woman the site found for him. After Raj Sheldon by hiding a dirty sock in his apartment, they meet his match Amy Farrah Fowler (Mayim Bialik). She acts exactly like Sheldon and they connect upon their aversion to dirty socks and their mothers' personalities. Sheldon offers to buy her a drink. Amy appears to like her date. Afterwards Howard comments "Good God, what have we done?"

Critics
"As we end season three I thought the writers addressed the Penny-Leonard relationship in a nice way. For both the relationship has changed their perspective on their future partners. The point was made in a somewhat subtle way that they both now have higher standards thanks to the other...It's a familiar refrain but the writers still don't handle Penny and Leonard's situation with the skill they need to...A passable end to a really decent season from The Big Bang Theory . "Really decent" might sound like damning with faint praise but the show has got better this season. The writing went to new places and did on occasion flesh out its characters." - The TV Critic's Review

Quotes

 * (Howard. Sheldon and Raj are at the café waiting to meet Amy Farrah Fowler.)
 * Amy Farrah Fowler: Excuse me, I'm Amy Farrah Fowler, you're Sheldon Cooper.
 * Sheldon: Hello, Amy Farrah Fowler. I'm sorry to inform you that you have been taken in by unsupportable mathematics designed to prey on the gullible and the lonely. Additionally, I am being blackmailed with a hidden dirty sock.
 * Amy: If that was slang, I'm unfamiliar with it. If it was literal, I share your aversion to soiled hosiery. In any case, I am here because my mother and I have agreed that I will date at least once a year.
 * Sheldon: Interesting. My mother and I have the same agreement about church.
 * Amy: I don't object to the concept of a deity, but I am baffled by the notion of one who takes attendance.
 * Sheldon: Well then, you might want to avoid East Texas.
 * Amy: Noted. Now before this goes any further, you should know, that all forms of physical contact, up to, and including coitus, are off the table.
 * Sheldon: May I buy you a beverage?
 * Amy: Tepid water, please.
 * (Both go to the counter, while Raj and Howard just stare.)
 * Howard: Good God, what have we done?

__________________________________________________________________________________

(Sheldon notices Penny taking Leonard to his bedroom)
 * Sheldon: What's going on?
 * Penny: Get your noise-cancelling headphones, 'cause it's gonna get loud.
 * Sheldon: Oh, not this again!

__________________________________________________________________________________


 * Sheldon: That's not afternoon. That's prevening.

__________________________________________________________________________________


 * Penny: Damn you, you rat bastard! In the olden days, I never would have known he was that stupid!

__________________________________________________________________________________


 * Zack: Is that the laser? It's bitchin'.
 * Sheldon: Yes. In 1917, when Albert Einstein established the theoretic foundation for the laser in his paper "Zur Quantentheorie der Strahlung", his fondest hope was that the resultant device be bitchin'.

Zack: Well, mission accomplished. __________________________________________________________________________________


 * Leonard: *Explaining the significance of the experiment to Zack* Think about what this represents. The fact that we can do this is the only way of definitively proving that there are man-made objects on the moon, put there by a member of a species that only 60 years before had just invented the airplane.
 * Zack: *Astonishingly* What species is that?

__________________________________________________________________________________


 * Zack: One question. How can you be sure it won't blow up?
 * Leonard: The laser?
 * Zack: The moon.

Trivia

 * The gang's lunar laser ranging experiment utilizes a, as is referenced on the whiteboard near Sheldon and Leonard's apartment door. crystal lasers typically emit light with a wavelength of 1064 nm, in the . However, the high-intensity pulses may be efficiently  to generate green laser light at 532 nm. Both of these wavelengths are written on the lower half of the whiteboard, along with the chemical formula Y3Al5O12 for the yttrium aluminum garnet crystal structure and the atomic transition 4F3/2 → 4I11/2 in the neodymium ion, after being "pumped" into excitation. The upper half of the whiteboard calculates the round-trip travel time of a light pulse bouncing off lunar retro-reflectors as 2.56 seconds, based on the ratio of the semi-major axis of the lunar orbit to the speed of light.
 * Sheldon refers to Albert Einstein establishing the theoretic foundation for the laser in his paper Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation) in 1917.
 * Sheldon mentions that he only drinks in months with an "r" in them. Thus, his quirk doesn't allow him to drink hot chocolate in the consecutive months of May, June, July, and August, which spans the summer season in the . It makes perfect sense; in, it would be much too hot in the summer months to drink hot chocolate.
 * This is Amy Farrah Fowler's first appearance in this series; interestingly, her full name is revealed even before her first appearance.
 * This episode is also Sara Gilbert's final appearance as Leslie Winkle. Interestingly enough, Leonard's final line in her scene- "She's not coming back" refers to both Leslie not taking him back and not returning to the series.
 * In "The Barbarian Sublimation", Sheldon described on-line dating algorthms as "Hokum" which is the same answer used by Raj and Howard for the question "How do you feel about online dating services?"