In the season eight finale, Sheldon and Amy get into a fight about commitment on their fifth anniversary. Amy tells Sheldon that she needs to think about the future of their relationship, unaware that Sheldon was about to propose to her. Season nine sees Sheldon harassing Amy about making up her mind until she breaks up with him. Both struggle with singlehood and trying to be friends for the next few weeks until they reunite in episode ten and have sex for the first time on Amy's birthday.
The Canadian alternative rock band Barenaked Ladies wrote and recorded the show's theme song, which describes the history and formation of the universe and the Earth. Co-lead singer Ed Robertson was asked by Lorre and Prady to write a theme song for the show after the producers attended one of the band's concerts in Los Angeles. By coincidence, Robertson had recently read Simon Singh's book Big Bang, and at the concert improvised a freestyle rap about the origins of the universe. Lorre and Prady phoned him shortly thereafter and asked him to write the theme song. Having been asked to write songs for other films and shows, but ending up being rejected because producers favored songs by other artists, Robertson agreed to write the theme only after learning that Lorre and Prady had not asked anyone else.
Amy enthusiastically accepts Sheldon's marriage proposal. However, when dining with Amy's colleagues later that night, Sheldon is offended that they are more impressed with Amy's work than his own. With help from Stephen Hawking, Sheldon later comes to grips with the fact that he will not always be the center of attention in the marriage. Bernadette is shocked to realize that she is pregnant again. She and Howard are not thrilled at the idea of having another baby so soon after their first. They attempt to convince Leonard and Penny to have a child as well, but are rebuffed.
I read through the article and all the comments (which makes me miss TBBT even more and it hasn’t been off the air a week yet) and noticed that 3 of my favs aren’t mentioned. (1) episode where a bully (Todd Sornecki) steals Sheldon’s online trophies and Penny kicks him in the nuts for Sheldon; (2) the episode where they reveals each others secrets (Leonard slept with Priya; Raj used Sheldon’s tooth brush; Howard told Raj foreigner give gifts to Americans for certain holidays and Sheldon put moths in Leonards food “for science”; (3) the episode where Amy and Sheldon go to the aquarium “as friends”, when Sheldon tells Amy “I can handle a lot of things Amy but getting over you isn’t one of them, I think we should just be friends” it breaks my heart everytime; (4) the episode where Priya buys Leonard glass and he walks into the cafeteria and causes mass chaos, that’s a classic; (5) the episode where Priya ruins the roommate agreement between Sheldon and Leonard, when Leonard buys Sheldon Greek food it’s hilarious. Sheldon gets back at Leonard & Priya by threatening to send an email to Priya’s parents telling that “she’s in a relationship with the whiter than marsmellow fluff Leonard Hofstedter”. Ok just one more, when they all take a road trip to speak at the science convention and Bernadette runs into her former professor/lover played by Rick Foxx and Sheldon banished Penny to the “love car” and Bernie and Howard sing Sonny & Cher “I got you Babe” is funnier than hell. I still crack up when I see Raj look down at Howard’s junk to measure Howard’s junk against Rick Foxx’s, I can’t believe the sensors let that through.
The show originally centered on five characters living in Pasadena, California: Leonard Hofstadter and Sheldon Cooper, both physicists at Caltech, who share an apartment; Penny, a waitress and aspiring actress who lives across the hall; and Leonard and Sheldon's similarly geeky and socially awkward friends and co-workers, aerospace engineer Howard Wolowitz and astrophysicist Raj Koothrappali. Over time, supporting characters were promoted to starring roles, including neuroscientist Amy Farrah Fowler, microbiologist Bernadette Rostenkowski, physicist Leslie Winkle and comic book store owner Stuart Bloom.
Getting called into Human Resources for Amy's outburst, Mrs. Davis tells her and Sheldon they are blowing their chances at the Nobel Prize. Amy would be the fourth woman to win in Physics, pressuring her to be a role model for women everywhere. To calm down, they try a sensory deprivation tank, which Sheldon loves, but Amy's mood only worsens. Sheldon does not know how to help and ends up holding her while singing "Soft Kitty". A newly confident Amy goes back to Human Resources to be allowed to campaign again and shares a drink with Mrs. Davis. Meanwhile, Howard buys a scooter to ride with Raj like in the old days. Bernadette finds out and makes him sell it since it's too dangerous. Bert buys it and ends up meeting a nurse after he dislocates his arm in a wreck.
After Sheldon reminds the guys about the time they mined Bitcoin without him, the guys go on a quest to find their suddenly valuable missing cryptocurrency. They realize the currency is on a laptop which Leonard gave to Penny when they dating, which she then gave to her ex-boyfriend Zack. After Leonard and Penny go to Zack's apartment, he shows them a seven-year-old video that Penny recorded on the laptop soon after she broke up with Leonard. Leonard is touched by the video which shows a drunk Penny lamenting the break-up of her relationship with him.