"The Recombination Hypothesis" is the 13th episode of the fifth season, as well as the 100th episode overall, of the American television sitcom The Big Theory. 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.
All that said, the writers have said that one of their ideas had been to not have Penny and Leonard end up together. But, at some point they knew they couldn't keep putting them together and then breaking them up. In the end, they kept them together.
The Staircase Implementation - The Big Theory (Season 3, Episode 22) - Apple TV.
"The Big Theory" The Romance Recalibration (TV Episode 2017) - IMDb.
So in The Big Theory season 7, episode 12, The Hesitation Ramification," Penny haphazardly proposed to Leonard while she was reeling about being cut from NCIS.
In Season 3 of The Big Theory, Penny and Leonard break up primarily due to the challenges in their relationship stemming from their differing expectations and emotional maturity. The breakup occurs in the episode titled ``The Lunar Excitation'' (Season 3, Episode 23).
Roommate agreement with apartment flag logo. The Roommate Agreement was written by Sheldon and was signed by Leonard when they first became roommates. These events were shown during a flashback in "The Staircase Implementation".
It dictates what Leonard has to eat each day of the week, what TV shows he is allowed to watch, whether he has a girlfriend stay over, that he has to drive Sheldon everywhere he wishes to go, whenever he wishes. It even dictates when Leonard is allowed to use the bathroom.
Frank and Alicia are some friends of Sheldon, who are only mentioned in "The Fermentation Bifurcation". Sheldon mentions them as alternatives to his regular friends whom he figuratively likes to keep under his sink and have to maintain a little mystery with his regular friends.