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.
When Leonard receives a braggy Christmas letter from his brother, he feels bad about how little he and Penny have achieved in the past year. Leonard wonders if he and Penny should be thinking about the next step after two years of marriage, like buying a house or having a baby. Penny tells him she wants to do all those things someday, but she has a bunch of stuff she would like to do first.
Science has also interfered with the characters' romantic lives. Leslie breaks up with Leonard when he sides with Sheldon in his support for string theory rather than loop quantum gravity.[70] When Leonard joins Sheldon, Raj, and Howard on a three-month Arctic research trip, it separates Leonard and Penny at a time when their relationship is budding. When Bernadette takes an interest in Leonard's work, it makes both Penny and Howard envious and results in Howard confronting Leonard, and Penny asking Sheldon to teach her physics.[71] Sheldon and Amy also briefly end their relationship after an argument over which of their fields is superior.[72]
"The Locomotive Manipulation" is the first episode in which Sheldon initiates a kiss with Amy. Although initially done in a fit of sarcasm, he discovers that he enjoys the feeling. Consequently, Sheldon slowly starts to open up over the rest of the season, and starts a more intimate relationship with Amy. However, in the season finale, Sheldon leaves temporarily to cope with several changes and Amy becomes distraught. However, in "The Prom Equivalency", he hides in his room to avoid going to a mock prom reenactment with her. In the resulting stand-off, Amy is about to confess that she loves Sheldon, but he surprises her by saying that he loves her too. This prompts Amy to have a panic attack.

The Big Bang Theory premiered in the United States on September 24, 2007 on CBS. The series debuted in Canada on CTV in September 2007.[152] On February 14, 2008, the series debuted in the United Kingdom on channels E4 and Channel 4.[153] In Australia the first seven seasons of the series began airing on the Seven Network and 7mate from October 2015 and also gained the rights to season 8 in 2016, though the Nine Network has rights to air seasons nine & ten.[154][155] On January 22, 2018, it was announced that Nine had acquired the rights to Season 1–8.[156]
"The Plagiarism Schism" -- Pictured: Howard Wolowitz (Simon Helberg) and Bernadette (Melissa Rauch). Kripke (John Ross Bowie) has proof that Dr. Pemberton (Sean Astin) plagiarized his thesis in college, and Sheldon and Amy aren\'t sure if they should turn him in or not. Also, Wolowitz is happily surprised to learn that Bernadette wasn\'t the only waitress at the Cheesecake Factory who had a crush on him back in the day, on THE BIG BANG THEORY, Thursday, May 2 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Photo: Michael Yarish/Warner Bros. Entertainment Inc. © 2019 WBEI. All rights reserved. (Photo: Michael Yarish, Warner Bros.)
With Leonard, Howard, Raj, and Amy accomplishing so much on their respective projects, Sheldon is forced to admit he has nothing important upon which to work. He makes Amy leave the apartment for a few days so he can focus, but cannot come up with any ideas and calls his mother as a distraction. Leonard and Amy have fun recreating experiments from when they were growing up, boring Penny, so she eats with Sheldon as he mulls over his scientific studies. Penny helps him realize that his study of dark matter is his rebound science from string theory, which Sheldon admits he never truly disregarded, but explaining string theory to her inspires Sheldon, helping him discover a potential breakthrough in the field. Meanwhile Howard is too busy with his family to be in the band with Raj, so Raj brings in Bert. But, when Howard annoys Bernadette by writing an astronaut-themed musical while she is on bed-rest, she makes him rejoin the band. The three are poorly received at a Bar mitzvah after singing Bert's original song about the boulder from Indiana Jones .
Sheldon and Amy struggle to choose a best man and maid of honor from their friends. They secretly decide to test and score them, allowing everyone to have an equal shot at either role. Once the gang finds out, none of them apart from Bernadette and Stuart want to be in the wedding. Sheldon settles for Stuart as best man but, once Leonard tells Sheldon that, as the groom, the decision is his alone, he picks Leonard. Amy is set to call Bernadette but, once Penny realizes Amy is her best friend, she immediately pitches herself for the position and Amy enthusiastically chooses her. Amy later makes Penny tell Bernadette the bad news.

Star Trek in particular is frequently referenced and Sheldon identifies strongly with the character of Spock, so much so that when he is given a used napkin signed by Leonard Nimoy as a Christmas gift from Penny he is overwhelmed with excitement and gratitude ("I possess the DNA of Leonard Nimoy?!").[73] Star Trek: The Original Series cast member George Takei has made a cameo, and Leonard Nimoy made a cameo as the voice of Sheldon's vintage Mr. Spock action figure (both cameos were in dream sequences). Star Trek: The Next Generation cast members Brent Spiner and LeVar Burton have had cameos as themselves,[74][75] while Wil Wheaton has a recurring role as a fictionalized version of himself. Leonard and Sheldon have had conversations in the Klingon language.
The first and second seasons were only available on DVD at their time of release in 2008[197] and 2009.[198] Starting with the release of the third season in 2010[199] and continuing every year with every new season, a Blu-ray disc set has also been released in conjunction with the DVD. In 2012, Warner Bros. released the first two seasons on Blu-ray,[200] marking the first time that all episodes were available on the Blu-ray disc format.
Warner Bros. Television controls the online rights for the show.[159][160] Full episodes are available at tv.com, while short clips and recently aired full episodes are available on cbs.com.[161] In Canada, recent episode(s) and pictures are available on CTV.ca.[162] Additionally in Canada, the first six seasons are available for streaming on Bell Media's CraveTV.[163] After the show has aired in New Zealand the shows are available in full online at TVNZ's on demand web service.
Kaley Cuoco's life after The Big Bang Theory is going to be animated. Cuoco has signed on to voice and executive produce DC Universe's new Harley Quinn series. She'll play the titular character in the new streaming series targeted toward mature audiences. In 2017, she got the rights to The Flight Attendant, a miniseries based on the book of the same name, which she was poised to star in. The Flight Attendant follows Cassandra Bowden, a flight attendant, who wakes up, hungover, in her hotel room with a dead body next to her. She goes about her day and heads back to New York. is she the killer? That's what she wonders. "This is the first time I have a project that I'm kind of nurturing from the beginning, so it's been a really interesting experience," she told PopSugar in March. "It's got a lot of aspects. It's very sexy. It's a really well-written book, which is why I wanted to option it. I'm ready to bring the character to life."
Raj hooks up with a recently separated woman, Nell, after one of his lectures at the planetarium. Her husband, Oliver, confronts Raj at the planetarium and then breaks down over the end of his marriage. After comforting Oliver, Raj talks to Nell and convinces her to give her husband another chance. Meanwhile, after diving once again into string theory and sprawling his work across his and Amy's apartment, Sheldon approaches a reluctant Leonard and Penny and convinces them to let him use his old room to study for a three-day trial period with an agreement to be quiet and stay out of their way. Sheldon surprisingly sticks to this agreement, being a reasonably good guest, which shockingly frustrates Leonard to no end. After Leonard lets out his frustrations, Sheldon then renegotiates the guest tenancy agreement for an extra few days and resumes being his normal demanding self, much to Leonard's relief.
Sheldon cannot find the perfect wedding date and begins talking in his sleep, adopting the persona of a laid-back person who goes with the flow. Amy and Penny believe that his subconscious mind is trying to tell him to be more relaxed; his attempt to be so while wearing flip-flops ends in disaster. He decides to leave all the wedding planning to Amy while he wears a Star Trek uniform underneath his tuxedo. Meanwhile, Raj and Stuart both become interested in Bernadette's new coworker Ruchi. While she likes them both as friends, she does not want a relationship with anyone.
The Big Bang Theory started off slowly in the ratings, failing to make the top 50 in its first season (ranking 68th), and ranking 40th in its second season. When the third season premiered on September 21, 2009, however, The Big Bang Theory ranked as CBS's highest-rated show of that evening in the adults 18–49 demographic (4.6/10) along with a then-series-high 12.83 million viewers.[94] After the first three seasons aired at different times on Monday nights, CBS moved the show to Thursdays at 8:00 ET for the 2010–2011 schedule, to be in direct competition with NBC's Comedy Block and Fox's American Idol (then the longest reigning leading primetime show on U.S. television from 2004 to 2011).[95] During its fourth season, it became television's highest rated comedy, just barely beating out eight-year champ Two and a Half Men. However, in the age 18–49 demographic (the show's target age range), it was the second highest rated comedy, behind ABC's Modern Family. The fifth season opened with viewing figures of over 14 million.[96]
When Mayim Bialik first learned she had to say goodbye to neurobiologist Amy Farrah Fowler, she opened up about the show ending in a blog post, asking, "And now I start to figure out what next. Where will life take me? Where will this career go? What do I want?" Up next she has a voice role in The Inspector Chronicles, a quasi-parody of Doctor Who making the leap from short to feature film. She'll reprise her role as the voice of the Inspector's time machine, known as B.O.O.T.H. Aside from that, she doesn't have any major projects lined up, aside from preparing to not see her close-knit cast the way she'd grown accustomed to. "We'll have to see what our lives look like," she told Us Weekly in early May about the chance they'll remain close. "I mean, we're all going to be on different schedules now; it's very different." 
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