The Lunar Excitation

The Lunar Exitation is the twenty-third episode and the final epiosde of the third season of the CBS 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 laser 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 Apollo 11. Leonard thinks Penny might enjoy that, so he goes to get her only to find she has male company. Penny and her date accompany them to the roof to observe the experiment. However, in the course of doing so Penny's date demonstrates himself to be extraordinarily dim witted thinking that they might blow-up the moon. Later that night Penny gets drunk and berates Leonard because he has ruined her ability to date stupid men. She sleeps with Leonard, but realizes it was a mistake the next morning. Leonard goes to ask Leslie Winkle to do the same, but gets turned down. After getting drunk, Leonard visits Penny's apartment and asks to sleep with her, which she declines leaving Leonard confused.

Meanwhile, Howard and Raj submit an online dating 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 and Howard blackmail Sheldon by hiding a dirty sock (an acute fear of his) in his room, 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. Afterwards Howard comments "Good God, what have we done?"

Quotes

 * (Howard, Sheldon and Raj are at the cafe 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?

Trivia

 * The gang's lunar laser ranging experiment utilizes a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, as is referenced on the whiteboard near Sheldon and Leonard's apartment door. Nd:YAG crystal lasers typically emit light with a wavelength of 1064 nm, in the infrared. However, the high-intensity pulses may be efficiently frequency doubled 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 retroreflectors 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 hot chocolate 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 Northern Hemisphere. It makes perfect sense; in California, it would be much too hot in the summer months to drink hot chocolate.
 * This is the Amy Farrah Fowler's first appearance in this series; interestingly, her full name is revealed even before her first appearance.
 * This is Sara Gilbert's final appearance as Leslie Winkle in this series.