The Big Bang Theory is centered on five characters living in Pasadena, California: roommates Leonard Hofstadter and Sheldon Cooper. A waitress and aspiring performer who resides across the hallway , penny. And Sheldon along with Leonard 's equally geeky and co workers and embarrassing friends , mechanical engineer Howard Wolowitz and astrophysicist Raj Koothrappali. Those four guys' geekiness and intellect is contrasted together with the social skills and good sense of Penny for effect.