Amy and Howard begin collaborating on a neuroprosthetics project, upsetting Sheldon and Raj, who feel they are not spending as much time with them. When they seek solace with an annoyed Bernadette, she exploits the situation to trick Sheldon into doing Howard's chores. Penny successfully employs the approaches recommended in one of Bernadette's parenting books to deal with Sheldon, but Leonard believes she is coddling Sheldon too much. Sheldon and Raj resolve the issue of missing their significant others by spending time together. 

David Saltzberg, a professor of physics and astronomy at the University of California, Los Angeles, checks scripts and provides dialogue, mathematics equations, and diagrams used as props.[4] According to executive producer/co-creator Bill Prady, "We're working on giving Sheldon an actual problem that he's going to be working on throughout the [first] season so there's actual progress to the boards ... . We worked hard to get all the science right."[5] David Saltzberg, who has a Ph.D. in physics, has served as the science consultant for the show for six seasons and attends every taping.[23] He sees early versions of scripts which need scientific information added to them, and he also points out where the writers, despite their knowledge of science, have made a mistake. He is usually not needed during a taping unless a lot of science, and especially the whiteboard, is involved.[24]
"Big Bang" thrived with the addition of new characters, including scientists Amy (Bialik) and Bernadette (Rauch) and comic-book-store owner Stuart (Kevin Sussman), says Helberg, part of the original cast with Galecki, Parsons, Cuoco and Nayyar. (The show eventually spawned a hit prequel spinoff, "Young Sheldon," which heads into its third season in the fall, most likely in the "Big Bang" time slot.)
While Jim Parsons was the one who'd had enough with The Big Bang Theory, opting not to renew his contract to play socially awkward theoretical physicist Sheldon Cooper and bringing about the demise of the show in the process, he won't be escaping the show's orbit entirely. He's still attached as both executive producer and narrator of prequel series Young Sheldon, returning for a third season on CBS this fall. "There was no factor; there was no situation that I was like, 'Well, I've had enough of that.' No. There was nothing like that. It was just…when you know, you know," he explained to The Hollywood Reporter in mid-May. 
In the apartment building where Sheldon, Leonard and Penny (and later Amy) live, the elevator has been out of order throughout most of the series, forcing characters to have to use the stairs. Stairway conversations between characters occur in almost every episode, often serving as a transition between longer scenes. The Season 3 episode, "The Staircase Implementation" reveals that the elevator was broken when Leonard was experimenting with rocket fuel.[89] In the penultimate episode of the series, the elevator is returned to an operational state, causing Sheldon some angst.

Showrunner Steve Molaro, who took over from Bill Prady with the sixth season, credits some of the show's success to the sitcom's exposure in off-network syndication, particularly on TBS, while Michael Schneider of TV Guide attributes it to the timeslot move two seasons earlier. Chuck Lorre and CBS Entertainment president Nina Tassler also credit the success to the influence of Molaro, in particular the deepening exploration of the firmly established regular characters and their interpersonal relationships, such as the on-again, off-again relationship between Leonard and Penny.[103] Throughout much of the 2012–13 season, The Big Bang Theory placed first in all of syndication ratings, receiving formidable competition from only Judge Judy and Wheel of Fortune (first-run syndication programs). By the end of the 2012–13 television season, The Big Bang Theory had dethroned Judge Judy as the ratings leader in all of syndicated programming with 7.1, Judy descending to second place for that season with a 7.0.[104] The Big Bang Theory did not place first in syndication ratings for the 2013–14 television season, beaten out by Judge Judy.[105]
Raj meets with the woman his father set up for him, Anu. Her commanding personality and practical approach to marriage startle Raj but he agrees to go ahead with it. Howard criticizes him but apologizes; he just never expected Raj to give up on romance. Raj admits this to Anu so she proposes to him, and he says yes. Raj also sends out a relationship questionnaire to Leonard and Penny, which soon reveals that Penny does not think she ever wants kids, upsetting Leonard, who would like to have kids someday, and their friends selfishly badger them on the issue. After telling her father Wyatt who is also upset, Leonard tells Penny that he'll be okay with it, as he never thought he'd have her in his life. To get his mind off of it, Penny rents Leonard a Batmobile to drive in and have fun with for the day. Meanwhile, Stuart starts bringing home Denise at night, which is very uncomfortable for Howard and Bernadette. When they also try to have time to themselves, they wake up their kids.
Amy and Howard begin collaborating on a neuroprosthetics project, upsetting Sheldon and Raj, who feel they are not spending as much time with them. When they seek solace with an annoyed Bernadette, she exploits the situation to trick Sheldon into doing Howard's chores. Penny successfully employs the approaches recommended in one of Bernadette's parenting books to deal with Sheldon, but Leonard believes she is coddling Sheldon too much. Sheldon and Raj resolve the issue of missing their significant others by spending time together.
Well done! Really great final episode writing. The characters we have enjoyed for 12 seasons went on with their lives. . .but reached a happy place at that moment of time. Amy and Sheldon recognized for their brilliance. Penny and Leonard growing into a family. Bernadette and Howard being concerned about the children. Raj having someone fun to attend the ceremony with. Way to tie things up on a pleasant note.
Keith Carradine has appeared in three episode as Penny's father, Wyatt, first in Season 4. Katey Sagal, who played the on-screen mother of Kaley Cuoco's character in the 2002-2005 sitcom 8 Simple Rules, has appeared as Penny's mother in one episode of The Big Bang Theory. Jack McBrayer has appeared in one episode of The Big Bang Theory as Penny's brother, Randall.
For the first three seasons, Galecki, Parsons, and Cuoco, the three main stars of the show, received at most $60,000 per episode. The salary for the three went up to $200,000 per episode for the fourth season. Their per-episode pay went up an additional $50,000 in each of the following three seasons, culminating in $350,000 per episode in the seventh season.[33][34] In September 2013, Bialik and Rauch renegotiated the contracts they held since they were introduced to the series in 2010. On their old contracts, each was making $20,000–$30,000 per episode, while the new contracts doubled that, beginning at $60,000 per episode, increasing steadily to $100,000 per episode by the end of the contract, as well as adding another year for both.[35]
Turning to total viewers, “Manifest” was the biggest gainer overall, on average adding 6.1 million viewers per episode. ABC’s “The Good Doctor” was second with an average viewer lift of just under 6 million. “New Amsterdam” (5.2 million viewer lift) and “A Million Little Things” (3.5 million viewer lift) were also among the top gainers in this measure, as was ABC’s “Whiskey Cavalier” (3.2 million viewer lift).
Howard and Bernadette's new neighbor Andy begins using floodlights mounted on his balcony that encroaches on their rear deck and hot tub. Investigating whether the lights comply with city code, they enlist Sheldon to help them with the paperwork, but Sheldon finds out Howard and Bernadette's own deck is also not code-compliant. He considers turning them in, but ultimately chooses friendship over the rules. He does report Andy though for violating property lines, allowing Howard and Bernadette to enjoy their deck again. Meanwhile, Bert wants to cut into a meteorite with Raj's help, rejecting Leonard's idea to use his laser to do so. Leonard dreams that he opens the meteorite with his laser, becomes possessed by an alien intelligence and eats Bert, Raj and Penny. He later apologizes to Raj and Bert, admitting he was jealous. The possibility of the meteorite unleashing a plague scares Stuart and Denise, who use it as foreplay for procreation, Stuart closing the store on Sheldon when he tries to browse.
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. 
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