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"The Change Constant" is the twenty-third episode of the twelfth season of the American sitcom The Big Bang Theory series. This is the 278th episode total, also being the penultimate episode of the series. It aired on Thursday, May 16, 2019, immediately prior to the series finale.


Sheldon and Amy await big news,[1] Sheldon has to deal with the attention and Amy decides to make some changes.

Extended Plot[]

The episode starts with flashbacks of many past episodes. 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 night. 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 and Leonard gets excited. Amy asks if Sheldon believes it, so Sheldon says that he could be dreaming. Leonard slaps him and then Sheldon shouts that they won the Nobel Prize and all four make an excited embrace.


Last scene of Kripke

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.


President Siebert's Last scene in the last episode Caltech appears

At the Caltech cafeteria, the guys are asking Leonard about how he struck Sheldon. President Siebert joins them and he wants their friends 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 Sheldon isn't in and then leads him to the cafeteria to talk and give his prospective as Sheldon's “best friend” and to tell outer space stories.

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.


Amy's new look.

Howard comes into the kitchen asking about dinner. On her computer Bernadette asks about the article on Sheldon 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. What kind of tea goes with that mood? 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 Penny 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 styled 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 surprised as he finds Penny waiting for him. She took the elevator down and she says it 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.


"Can you believe it? They finally fixed the elevator!"

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 is also married with a successful career and she 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 Apartment 4A, Amy likes how her hair looks. All of them are going to stop walking on eggshells with Sheldon. Leonard mentions both Sheldon's Spot and controlling the thermostat setting as examples. He is always cold and that is why he 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. It's suddenly become clear as to why Sheldon wanted no one to touch the model.


Out drinking with Sheldon talking about his problem with change.

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: The title refers to Penny pointing out to Sheldon that the only constant in life is change.
  • Taping date: April 23, 2019
  • This episode was watched by 18.52 million people with a rating of 3.2 (adults 18–49).
  • This episode aired in Canada on May 16, 2019.
  • Chuck Lorre's vanity card. [1]


  • Caroline Preece at Den of Geek! - The simplest thing to say about The Change Constant and The Stockholm Syndrome (which function well as a single episode) is that they do what they need to. No more, no less...That's not to say there isn't plenty to get annoyed about in this finale alone. Penny being pregnant is a massive insult to her character and doesn't play at all well considering the current news cycle...On the flip-side, I’ve actually come full circle on my feelings regarding a single Raj...Kripke and Bert get their victory laps, Leonard reveals that he's been chilly for 12 years because he still hasn't dared change the thermostat, and the elevator finally gets fixed...That final zoom-out was perfection. [2]
  • IMDb user review [3]


  • Last appearances of Barry Kripke, President Siebert, and Caltech, as well as the only post-Season 7 appearance of The Cheesecake Factory.
  • CBS aired this episode as the first half of a one-hour series finale, followed by "The Stockholm Syndrome." As such, it did not include the usual end credits or a Chuck Lorre vanity card. However, when the episode is aired separately in syndicated runs, or in the Blu-Ray/DVD releases of Season 12, both are included.
  • The elevator is finally fixed after being out of order for 16 years. The only other time the elevator was shown to be working was in "The Staircase Implementation," which was a flashback episode to 2003 when Leonard and Sheldon first met and became roommates (and showed why the elevator became inoperative in the first place).
  • The mystery of why Leonard wears hoodies frequently is finally revealed: it's always cold in the apartment, as 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 the closet, it instantly breaks into scores of pieces.
  • Amy gets a makeover in this episode after lamenting how "frumpy" she looks when she sees her pictures in the media. Unlike the partial makeover seen in the unaired, post-wedding tribute to Stephen Hawking, this one is permanent, as Amy states that she is done tiptoeing around Sheldon's insecurities.
  • Sheldon finally accepts that change is a universal constant (see episode title) and that things must change around him.
  • Penny gets pregnant on this night after she goes out drinking with Sheldon, though this was not revealed until the cold open of the next episode.
  • This is the last episode where we actually see any of the characters walk down all three flights of stairs (Sheldon and Amy after the first commercial break, then Sheldon by himself after the second break), as the elevator is now working. The characters do take the stairs one final time (while their massive amount of luggage rides the elevator) in the next episode, but we don't actually witness it (we only see them walk down the last few steps into the lobby).


Sheldon: Six times ten to the eight atoms of radium in a lead jar, six times ten to the eight atoms of radium in a lead jar. If the half-life of radium should happen to pass, three times ten to the eight atoms of radium in a lead jar.
Penny: Really hope you’re almost to zero.
Sheldon: No, see, that’s the beauty of half-lives. It’s impossible to determine when you’ll arrive at zero. It’s like “The Wheels on the Bus” if the bus had an unknowable number of parts.
Amy: Yeah, we’re going to need some coffee.
Penny: Yeah, I’m with you. Leonard, coffee?
Leonard: Black and strong like Luke Cage.
Penny: I’m too tired to be disturbed by that. Sheldon?
Sheldon: Hmm, absolutely not, no. The Nobel Committee will be making the calls to inform the winners at any minute, so the only drug I need is the endorphins pumping in my brain in anticipation of our victory.
Amy: Well, technically anticipations wouldn’t be mediated by endorphins as much as dopamine, but, you know, you’ve been up all night so I’ll give you that one. Really? The second he stops talking?
Penny: Well, should we wake him up?
Leonard: Well, he did say if he fell asleep, we were allowed to slap him awake.
Penny: Oh boy.
Leonard: Wait a minute. Why do you get to do it?
Penny: Cause I called it.
Leonard: Well, you can’t just call it. You have to earn it.
Penny: Oh, and you earned it?
Leonard: No one has earned it more than me.
Amy: Umm.
Leonard: You have your whole life to smack him around. This is my time.
Penny: Fine. Don’t miss.
Leonard: It’s not volley ball. I can handle it.
Penny: Oh, wait, hang on. When you’re old, you’ll gonna want a record of this.
Leonard: Oh, oh yeah. Do it in slow-mo. I want to see his cheeks wrinkle.
Penny: Ready, go.
Sheldon: [Phone rings.] It’s happening! Unknown caller. It has to be them.
Amy: Okay, put it on speaker.
Sheldon: Hello?
Amy: Hi?
Amy: Yes.
Sheldon: Yeah.
Kripke: Congratulations! It is my pleasure to inform that you have just won the Nobel Prize in being suckers!
Sheldon: His Swedish accent was very convincing. [Phone rings.] This is it! What do you want Howard?
Howard: We were just calling to see if you’d heard.
Sheldon: We Haven’t.
Amy: But thank you for getting up so early to call. That was very thoughtful.
Bernadette: Oh, please. We have two little kids. We’ve been up for an hour.
Howard: Did anyone get to slap Sheldon?
Leonard: No.
Bernadette: Okay, well call us when you hear.
Penny: All right, now what?
Sheldon: Oh, why don’t we play a game to pass the time? Here. I’m thinking of a number. Hint: It’s a cube of a cube of a prime.
Leonard: There’s an infinite number of possibilities.
Sheldon: So, you got somewhere else to be?
Amy: [Phone rings.] Oh, that’s me. Hello? Yes, this is Dr. Fowler. I see, Okay, thank you. We won.
Penny: [Gasps] Congratulations!
Leonard: Oh, my God!
Sheldon: We did it!
Amy: I know. Can you believe it?
Sheldon: That a good point. What if I’m dreaming? [Leonard slaps him.] We won the Nobel Prize! [Everybody screaming.]

Amy: And how does it feel to be married to a Nobel Prize winner?
Sheldon: You tell me. Oh, Amy-centric. What a fun way to look at it.
Amy: I think so.
Sheldon: You would, that makes sense. [Phone keeps ringing.] Oh, aww. It’s a congratulation text from my Meemaw. Oh, oh. And there’s one from my mom. Any my sister. Oh and my brother. And my brother’s ex-wife. My brother’s other ex-wife. Boy, they don’t tell when you win a Nobel it chews up your battery life.
Amy: [Phone keeps ringing.] Oh, that’s me. It’s CVS. My prescription’s ready. Oh, and also it’s my dad. He says congratulations and he loves me.
Sheldon: Nothing about me? [Phone rings.] Oh, it’s your dad. I’m good. You know, when you think about it, now that we’re Nobel Prize winners, our names will be linked together forever.
Amy: We’re married. Our names are already linked together.
Sheldon:Oh please, that’s just a piece of paper. This is a piece of paper and a medal.
Amy: It’s weird. I don’t really feel different, but I guess our lives will never by the same.
Sheldon: Oh, I don’t know. We’re going to work like always. I still put my pants on both legs at a time.
Amy: One day that’s gonna end very badly. [Leaving the building they are surrounded by reporters.]
Reporter1: Congratulations. How does it feel?
Amy: Okay, we’re happy to answer your questions, just one at a time please. [Sheldon runs away.]
Reporter2: Dr. Cooper?
Reporter3: Is Dr. Cooper coming back?
Amy: No. Next question.

Raj: Was it your left hand or your right hand?
Leonard: Right. Spit actually flew out of his mouth.
President Siebert: Hey, fellas. Can you do me a favor?
Raj: Do we have a choice?
President Siebert: Ha-ha. No. Sheldon and Amy are now officially superstars and the press will be reaching out to their family and friends for comment. So that we’re all on the same page the word we’re going to use to describe them is “quirky”. And not “quirky”, more like “quirky” [Squeaky.].
Howard: So not Mr. and Mrs. Wackadoodle?
President Siebert: Ho-ho-ho. You bitter envious little man.
Amy: [Sheldon and Amy enter to a round of applause.] Thank you so much. [Sheldon run out.]
President Siebert: And now we call that. Quirky.
Raj: Quirky.
Leonard: Quirky.
Howard: Quirky.

Reporter4: Dr. Cooper, can I have a minute of your time?
Howard: Hello? Hey. Can I help you?
Reporter4: Uh, yeah, actually. Uh, I had an appointment to interview Dr. Cooper about the Nobel.
Howard: Hang on a second. Sheldon? [Sheldon hiding behind his desk shakes his head no.] Sorry he’s not there.
Reporter4: Damn, I’ve got a deadline.
Howard: I don’t know if it helps you at all, but I’m his best friend in the whole world.
Reporter4: Really?
Howard: And an astronaut. Come on, you buy me a cup of coffee and I’ll tell you about both.

Raj: Everyone okay in there?
Amy: [Sobbing.] Go away!
Raj: Amy?
Amy: Raj, please. Not now.
Raj: Hey, what’s wrong?
Amy: My picture’s all over the Internet and I look terrible.
Raj: No. let me see. Well, that is an unfortunate angle. But who cares? You just won the Nobel. You should be proud of this moment.
Amy: I know I shouldn’t care about how I look, and I never thought I did. It’s stupid and shallow, but I just can’t help it. Am I really this frumpy?
Raj: No, you are a beautiful woman. By the way, if you are not happy with those pictures then make some changes. Get a haircut, new clothes, new glasses, bigger glasses, no glasses. Then you won’t be able to see those pictures.
Amy: Sounds expensive.
Raj: excuse me, if I’m not mistaken, the Nobel comes with a substantial cash prize. What were you gonna spend it on?
Amy: Hadn’t really thought about it. Sheldon got his eyes on some new Dockers.
Raj: Come on. Do something for yourself.
Amy: Well, I suppose I could get a haircut.
Raj: And some makeup and a new wardrobe and a little thank you gift for your shopping buddy if we see something he likes. Come on.
Amy: Where are we going?
Raj: Beverly Hills, where the things he likes are.

Howard: Dinner ready?
Bernadette: Not unless you cooked. Why is this article about Sheldon all about you?
Howard: Let me see. Oh, good, they used my NASA picture.
Bernadette: Why does it say you’re his best friend? Leonard’s his best friend.
Howard: No, Leonard has always been kind of a monkey butler. Whenever Sheldon got into a scrape I was his go-to guy.
Bernadette: When did he get into a scrape?
Howard: You’re kidding, right? Remember when he had a panic attack ‘cause his hand got stuck in a jar of olives? I was the one who told to let go of the olives.
Bernadette: Please, that doesn’t make you his best friend.
Howard: You know that reporter asked me if I could put him in touch with Amy’ best friend.
Bernadette: That’s Penny.
Howard: Doesn’t have to be.

Sheldon: Hmm. What kind of tea is appropriate for winning a Nobel Prize and now everything is changing and you feel unmoored from reality?
Leonard: I don’t know. Earl Grey?
Sheldon: You know, this is something I wanted my whole life. But I guess I never considered how everything would be different.
Leonard: Buddy, I know it all feels overwhelming right now, but I promise you it’ll settle down.
Sheldon: There’s no Earl Grey. You filthy liar!
Raj: Hey, is Penny here?
Leonard: No, why?
Raj: I wanted to show her my latest creation. I give you, Dr. Amy Farrah Fowler.
Leonard: Wow Amy, you look amazing.
Amy: Thank you. Well, Sheldon what do you think?
Sheldon: I liked you better the way you were.
Raj: But she looks beautiful. Classic lines, colors that complement her skin tones, and hair that goes from “office” to “on the town” in minutes.
Sheldon: I don’t care. Put it back.
Amy: I like the way I look.
Sheldon: Well, I don’t.
Leonard: My fault. I was out of Earl Grey. Sheldon, that was really rude.
Sheldon: I’m sorry. Amy was the one constant I could count on, and now she’s changing.
Leonard: It’s just a haircut and some clothes.
Sheldon:: No, it’s the last straw. [Elevator rings and Penny appears.]
Penny: Can you believe it? They finally fixed the elevator.
Sheldon: This is a nightmare! [Runs down the stairs.]
Penny: What’s with him?
Leonard: He won a Nobel Prize and his wife looks amazing.
Penny: Oh, yeah. Got it. [Sheldon runs into Penny in the lobby.]
Sheldon: [Panting.] How did you get down here?
Penny: The elevator. It’s really fast.
Sheldon: I need to be alone right now. Don’t try to follow me.
Penny: All right. Need a ride?
Sheldon: That would be great. Thank you.

Amy: I should’ve seen this coming.
Raj: Oh stop, you’re allowed to get a haircut.
Amy: I know. But I should’ve done it gradually. You know, like maybe 300 tiny haircuts over a ten-year period.
Leonard: Okay, you need to focus on the positive. You won a Nobel Prize. I slapped Sheldon. A lot of dreams came true today.
Amy: You know, you’re right. This is a huge day for me, and I’m allowed to enjoy it without how it’s going to affect my husband.
Raj: Is it me or did it just get fierce in here?

Sheldon: All this change is just too much. The reporters, the attention at work, and now even Amy’s changed. Whoa, whoa, whoa. Slow down.
Penny: I’m playing a drinking game. Every time you say the word “change” I’m taking a slug.
Sheldon: Are you gonna be able to drive me home?
Penny: Hmm. Not unless you change the subject. Huh. Now I said it. Meh. Hmm. You know, you’re the only person who could win the biggest prize in science and still be upset about it.
Sheldon: It’s just all the times I thought about winning I never thought how it would ch….affect my life. I’m sorry. I’m genuinely concerned about your liver.
Penny: Okay. Fine. I’ll stop playing. You know, you go on and on about wanting things to stay the same, but you’ve change a lot since I met you.
Sheldon: Oh, you are a mean drunk.
Penny: I’m serious. You have a ton of friends, you got married, moved into a new apartment, you wore a baseball hat that one time. Heck, you had sex almost as many times as I have fingers.
Sheldon: More, by this many.
Penny: You dog!
Sheldon:It was the Avenger’s trailer.
Penny: Oh. Mmm. I’ve grown too. I used to be the bartender back there.
Sheldon: That’s true. And now there’s a completely different woman who botched by drink order. How hard is 65% Coke 35%, Diet Coke?
Penny: Well, judging by the look on her face, it’s at least one percent saliva.
Sheldon:I do take your point. You know, you’re also married, you have a successful career, you no longer dress like your trying to attract sailors by the wharf.
Penny: So I guess the only thing that actually stays the same is that things are always changing.
Sheldon: Interesting. So you’re saying the inevitability of change might be a universal constant.
Penny: Well, there’s a little more to it than that, but, yeah sure.
Sheldon: Hey look, that’s Bernadette.
Bernadette: [on TV] I can’t tell you how many times Dr. Fowler was gonna give up and I would say to her, “Amy, as your best friend, I’m not gonna let you quit.”
Penny: Okay, I’m drinking again.
Sheldon: I’ll join you. Waitress. 95% Hawaiian Punch, 5% vodka.
Howard: [on TV] Let me tell you Mr. Nobel Laureate wanted olives…
Bernadette: [on TV] That was a good one.
Sheldon: You know what. 90/10.

Amy: You know, I like the way my hair looks. I’m done tiptoeing around him.
Raj: We’re all guilty of it.
Amy: But why?
Leonard: Cause we’re afraid to upset him.
Raj: Which happens anyway.
Amy: Well, that’s over.
Leonard: I’m done enabling him. Like, this is his spot, and..and the thermostat has to be set to his comfort level, even though he doesn’t live here anymore, and I’m always chilly.
Raj: Is that why you wear a hoodie all the time?
Leonard: Why would…yes! To accommodate Sheldon! And what..what is this…this thing? Why is it here? I’ll tell you why. Because it was here when I moved it and, for no earthly reason, he forbade me to touch it.
Amy: Well, if you don’t like it get rid of it. Put it in the closet.
Leonard: You know what, I will. [Molecule model collapses.]
Raj: I bet that’s the reason.

Penny: Hang on. What do you think? Want to give it a try?
Sheldon: Well, you know, the elevator did work when I moved into the building. So going up and down the stairs was a change, so this would actually be a return to the status quo. But conversely I think…
Penny: Get in. [Shoves Sheldon into elevator and smiles as the door closes.]
Sheldon: This is wild.