Episode 20: The Hofstadter Isotope -

"The Hofstadter Isotope," the 20th episode of The Big Bang Theory second season, originally aired on April 13, 2009, featuring Penny's date with Stuart Bloom, the comic book store owner. The episode highlights Leonard's jealousy and marks the debut of Kevin Sussman as Stuart. For more details, visit Apple TV .

"The Big Bang Theory" The Hofstadter Isotope (TV Episode 2009) - IMDb Episode 20: The Hofstadter Isotope