"The Change Constant" is the twenty-third and penultimate episode of the twelfth season of the American sitcom The Big Bang Theory. This episode is the penultimate episode of the entire series. It aired on Thursday, May 16, 2019 immediately prior to the series finale.


Sheldon and Amy await big news.[1]

Extended Plot

Early in the morning Leonard, Penny and Amy are falling asleep while Sheldon sings about the half-life of radium waiting to hear if they had won the Nobel Prize. Penny and Amy jump up to make coffee. Sheldon doesn’t need any since the anticipation is enough drug for his brain to produce endorphins. Amy corrects him that its dopamines, but she realized that he’s been up all might. Then Sheldon falls asleep. Leonard gets excited because Sheldon had told them to slap him if he did fall asleep. Leonard feels that he’s paid enough dues with Sheldon to get the honor. Before he has a chance, the phone wakes Sheldon up. It’s only Kripke tricking them into thinking he is the Nobel committee. The phone rings again, but its only Howard and Bernadette checking in on them. Sheldon suggests that they play a number guessing game, when Amy’s phone rings. She quietly answers it, thanks them and then quietly tells everyone that that they won. Penny gets excited. Amy asks if Sheldon believes it, so Sheldon says that he should be slapped so that he knows that he isn't dreaming. Leonard slaps him. Sheldon shouts that they won the Nobel Prize and all four make an excited embrace.

Coming down the stairs, Sheldon and Amy discuss winning as Sheldon gets congratulatory texts from Meemaw, his mother, Missy, George and both of his brother's ex-wives. Amy gets a text from CVS and from her father, who also sends one to Sheldon. Sheldon tells Amy that their names will be linked forever. Amy reminds him that they are already married. Sheldon explains that that is a piece of paper and the Nobel is a piece of paper and a medal. Again they feel their lives will never be the same, however; Sheldon said that they’ll still go to work and put their pants on one leg at a time. He is proven wrong when a large group of reporters are waiting for them outside of the building. Sheldon is spooked and runs away. Amy is asked whether Dr. Cooper is returning. She replies no and asks for the next question.

At the Caltech cafeteria, the guys are asking Leonard about how he struck Sheldon. President Siebert joins them and he wants their friend to describe the new superstars of physics as “quirky”. Howard jokes that they shouldn’t call them “Mr. and Mrs. Wackadoodle.” The President calls him a bitter and envious little man. The Coopers enter the cafeteria and are applauded though Sheldon quickly leaves. And the President leads the guys in describing his behavior as “quirky”.

Howard walks by Sheldon’s office and finds a reporter knocking on his door. Howard looks in and finds Sheldon hiding behind the desk shaking his head no that he doesn't want to see him. Howard tells the reporter he isn’t in and then leads him to the cafeteria to talk and give his prospective as Sheldon’s “best friend”.

Raj passes by the ladies’ room and hears Amy crying. He checks in on her and she tells him that she looks so terrible in the photos posted on the Internet. She realizes that it is stupid and shallow, but doesn’t like looking so frumpy. Raj calls her a beautiful woman and if she doesn’t like it, she can make some changes. New clothes and a new haircut. Amy thinks that that sounds expensive, but Raj reminds her that she is getting a substantial cash prize with the Nobel. Raj is going to help her, so they head off to Beverly Hills.

Howard comes into the kitchen asking about dinner. On her computer Bernadette asks about the article that talks more about him instead of his “best friend” Sheldon. Howard reacts that Leonard was more of Sheldon’s "monkey butler" rather than his best friend. The reporter also wanted Howard to put him in touch with Amy’s best friend. Bernadette says that that is Penny. Howard adds that it doesn’t have to be as they smile at each other.

Sheldon and Leonard are having tea together as Sheldon laments all the changes that make him feel unmoored from reality. Leonard suggests Earl Grey tea, but they don’t have any. Sheldon has wanted a Nobel Prize all his life, but never really thought about the consequences. Raj comes in wanting to show Sheldon his latest creation, the new and improved Dr. Amy Farrah Fowler. In comes Amy in a classy sleeveless dress and coat wearing larger glasses and a shorter haircut looking very happy. Leonard thinks that she looks amazing, but Sheldon prefers the old Amy. Amy looks disappointed as Sheldon runs out with Leonard following. Out in the hallway Leonard calls him rude. Sheldon explains that Amy was the one thing he could count on that didn’t change. Sheldon claims that that is the last straw as the elevator doors open and out walks Penny. “Can you believe it? They finally fixed the elevator.” Sheldon calls it a nightmare and runs down the steps. In the lobby he is scared as he finds Penny waiting for him. The elevator is really fast. Sheldon has to be alone, but he doesn’t mind Penny providing transportation.

Back in Apartment 4A, Amy says that she should have seen this coming and that she should have changed her hair slowly over ten years. Also she realizes she has had a big day and should be able to enjoy it without worrying about how it affects Sheldon.

Penny is having a drink at the Cheesecake Factory with Sheldon who is complaining about all the changes which include Amy. Penny is taking a drink every time Sheldon uses the word “change”. Penny then tells him that he’s the only person in the world who could win a Nobel Prize and still be upset about it. She reminds him how much he has changed having friends, being married, living in a new apartment, wearing a baseball cap and having had sex almost as many times as Penny has fingers. Actually he’s had it two more times than that number. Penny adds that she used to be the bartender. Sheldon comments that there is someone new that also gets his drinks wrong. Sheldon adds that Penny no longer dresses like she is trying to attract sailors on the wharf. Penny concludes that since changes keep occurring, then the fact that things change is a constant. Sheldon interprets that as that the inevitability of change might be a universal constant. Then on the television they see Howard and Bernadette talking about the Coopers and she is claiming to be Amy’s best friend. Penny goes back to drinking. Sheldon then joins her as Howard claims to be his best friend.

Still back in 4A, Amy likes how her hair looks. All of them are going to stop tip-toeing around Sheldon just so he won’t get upset. They feel like they were being enablers. Leonard mentions both Sheldon’s spot and the thermostat setting as examples. He is always cold and that is why is keeps wearing hoodies. Then Leonard mentions the DNA model that has been there since Leonard moved into the apartment, which Sheldon forbade anyone to touch. Amy suggests that he put it in the closet. Leonard agrees, but as he tries to move it, hundreds of balls (atoms) fall off of it.

Penny and Sheldon enter the lobby as Sheldon heads up the stairs. Penny asks Sheldon if he wants to try the elevator. Sheldon mentions that it did work when he moved into the building. The repaired elevator is a return to the status quo. Penny just pushes him into the elevator. She smiles not having to walk up and Sheldon calls the ride “wild”.



  • Title Reference: Penny pointing out to Sheldon that the only constant in life is change.
  • Taping date: April 23, 2019
  • This episode was watched by xx.xx million people with a rating of xx.xx (adults 18-49).
  • Total viewers including DVR users xx.x million.
  • This episode aired in Canada on May 16, 2019.
  • Chuck Lorre's vanity card.


  • To be entered.
  • IMDb user review


  • Ninth episode of the last ten episodes.
  • On the final night of TBBT, CBS aired two episodes. This is the first episode that aired that night and the penultimate episode of Season 12 and of the entire series.
  • The elevator is finally fixed.
  • The last night of new episodes of The Big Bang Theory.
  • Leonard wears hoodies because it is always cold in the apartment; Sheldon forbade him to touch the thermostat even after he moved out.
  • Sheldon and Amy have had sex 12 times.
  • Sheldon forbade Leonard to touch the DNA sculpture in the apartment, which was present when Leonard moved in. The reason for this is because it is actually fragile; when Leonard picks up the sculpture to move it into a closet, it instantly breaks into pieces.
  • Amy gets a makeover, which might have occurred after her wedding. In the unused tribute to Stephen Hawking, the newly married Amy was not as classy as in this episode, but did have a new hairdo and had ditched her plaids and patterns.


To be entered.