<Tr> <Td> ← Previous "The Shiny Trinket Maneuver" </Td> <Td> Next → "The Beta Test Initiation" </Td> </Tr> <Tr> <Td_colspan="2"> The Big Bang Theory (season 5) List of The Big Bang Theory episodes </Td> </Tr> <P> "The Recombination Hypothesis" is the 100th episode of the American sitcom The Big Bang Theory and the 13th episode of the series' fifth season . It premiered on CBS in the United States on January 19, 2012 . In this episode, Leonard impulsively asks Penny out for dinner on a date . </P> <P> The story and concept of the episode was written by series co-creator Chuck Lorre . The teleplay was written by co-creator Bill Prady and writer Steven Molaro . "The Recombination Hypothesis" was directed by Mark Cendrowski . The episode received good reviews from television critics who spoke positive about Leonard and Penny trying to rework their relationship . Upon airing, "The Recombination Hypothesis" garnered 15.71 million viewers in the United States and 5.3 rating in the 18--49 demographic, according to Nielsen ratings . </P>

When do leonard and penny start dating again