The Bat Jar Conjecture - S1-E13
Trivia: When Leonard, Howard and Raj are contemplating who to have as the fourth member of their Physics Bowl team, Raj says, "You know who's apparently very smart is the girl who played TV's 'Blossom'. She got a Ph.d in Neuroscience or something." The girl he's referring to is actress Mayim Bialik, who plays Amy Farrah Fowler in later episodes of The Big Bang Theory. Interestingly, she is the only recurring cast member on the show that actually does have a Ph.d in real life.
Chosen answer: The song is called "Dark as a Dungeon" and was written and first performed by singer-songwriter Merle Travis in 1946. It has been performed by a wide array of artists, including Tennessee Ernie Ford, Harry Belafonte, Dolly Parton, Queens of the Stone Age, Kathy Mattea and Amy Grant. But it was made most famous when it was performed and recorded by Johnny Cash during his concert at Folsom Prison in 1968. According to Wikipedia: "It is a lament about the danger and drudgery of being a coal miner in an Appalachian shaft mine. It has become a rallying song among miners seeking improved working conditions."
Michael Albert