Leonard tells Zack and Marissa he will father their child, but Penny tries to seduce him despite knowing he has to be abstinent for a few days. Her visiting father, Wyatt, points out her actions suggest she is more conflicted over having kids than she lets on, which she admits. Wyatt says he will support her no matter what. Meanwhile, Sheldon and Amy warn that he will not be allowed to raise a child that is not his. Leonard decides not to go through with it; he tells Zack to have Sheldon be the donor, but Amy forbids it. Meanwhile, Howard turns Raj's cancelled bachelor party into a couples' trip into a zero-gravity aircraft, though he's convinced that Bernadette would hate it. Bernadette tries to get out of it so Howard sits out, forcing Bernadette to go through with it just to prove him wrong, though she does not enjoy it.
Howard and Raj are still fighting, so Howard dis-invites Raj to Halley's birthday party. However, when Stuart pulls out as party planner at the last minute, Raj agrees to plan the party, which doesn't turn out too well due to Halley being asleep, Bernadette being on bed rest, and no people turning up. When Howard and Raj get into a shoving match in the party's bounce house, they end up letting out their frustrations, but also having fun and reconciling. Leonard is depressed upon receiving his successful brother's Christmas card and attempts to make a list of what he and Penny accomplished this year, not coming up with much. This prompts them to think about their plans for the future, so they decide to go on trips and achieve more out of life together before starting a family. Sheldon cooks Amy a Little House on the Prairie-themed birthday dinner, which gives them both food poisoning. They eventually recover enough to attend Halley's birthday party with the others, where they have fun in the bouncy castle and then have sex in Howard and Bernadette's house.
As the theme of the show revolves around science, many distinguished and high-profile scientists have appeared as guest stars on the show. Famous astrophysicist and Nobel laureate George Smoot had a cameo appearance in the second season. Theoretical physicist Brian Greene appeared in the fourth season, as well as astrophysicist, science populizer, and physics outreach specialist Neil deGrasse Tyson, who also appeared in the twelfth season.
As Sheldon and Amy start to plan their wedding, they use decision theory to limit the stress of choosing between their competing visions for the big day. After they begin to question each other’s decisions and make deliberately provocative choices, they decide to have a simple wedding at City Hall. As they wait their turn, Sheldon changes his mind and decides he wants a first dance with Amy at a real wedding.
The CBS sitcom said goodbye on Thursday night after a storied 12-season run — and now that it’s really over, we’re feeling super nostalgic. Having already revisited the pilot episode, highlighted classic “Shamy” moments and ranked our favorite recurring characters, we’re closing out our retrospective coverage with a list of the 10 episodes that we feel are a cut above the rest.
^ "Editor's Note: With final Monday ratings in, The Big Bang Theory has now reached a new series high in viewers (16.32m) and was the night's top program in adults 18-49 (5.9/15), up a tenth from this morning. -- "Two and a Half Men" Soars to Its Best Adult 18-49 Rating in Three Years". CBS. March 9, 2010. Archived from the original on January 8, 2014. Retrieved January 5, 2013.