Sheldon considers his origin (0, 0, 0) intransgressible, and beyond his origin certain habitual constants are required to maintain his absoluteness. With difficulty, he can integrate new variables into his sphere, accept with loose limitations some new object or information, but the stress—the effort—required to integrate these new variables is with few exceptions not worth the expenditure of energy, because if those variables are ever removed from Sheldon's closed system of existence, his system will—will surely—
His mother would put it another way. "Shelly," she would say, "what you're afraid of ain't change. What you're afraid of is heartbreak."
Amy moves away.
Sheldon does not miss her.
Amy moves away.
That most of Sheldon's routines remain unchanged is inconsequential.
He takes to invading Penny's apartment again, and she (more or less) lets him. "Bring your own spoon," she tells him one night, and he shows up at her door, confused but obedient, carrying a wooden cooking utensil. "Not that kind of spoon," she says, and sends him back to his apartment, aware that using any of her flatware will require that most of the evening be devoted to sanitation rituals. He returns with a metal teaspoon from his own, separate drawer, the one with the UV lights, the one that Leonard is not allowed to touch. Penny lets him in, shows him the ice cream carton, shows him how it remains sealed, how she's kept it in the freezer at the appropriate temperature, tells him that she bought it at the gas station around the corner and brought it immediately home. "And it was cold outside, so," she says. "No chance to thaw."
"Acceptable," Sheldon says, and then adds, because Amy believed the manners were a droll but necessary social lubricant (in this as in few things she had been in concordance with his mother), "Thank you."
And so it is Penny and not Leonard who fulfills the function of best friend (requirements: ability to drive, flexible sense of morality, affinity for Batman; duties: solace in the face of illness, companionship at midnight releases, driving). Penny says it's okay, that they can get over their broken hearts together, that this is what friends do, that they should make margaritas, that they'll get over it eventually, that Amy and Leonard don't know what they're missing. Penny says...much.
"The common social paradigm dictates that you and I hate one another, though," Sheldon points out. He is on his second carton of Ben and Jerry's, and is feeling dangerously gluttonous. "You, as Amy's best friend, and I, as Leonard's best friend, are under the social contract natural enemies."
"Well, yeah, I guess that's true," Penny says, sucking the last drops of Americone Dream from her spoon (plastic, lime green, of dubious hygiene and origin). "But hey, you and I were friends before I ever went out with Leonard, right? That takes precedence."
"Does it?" Sheldon says. He doesn't intend to be dubious, but some measure of skepticism must express itself on his features, because Penny scowls.
"Yes, Sheldon, it does. Because I say so. Look, who's the expert on break-ups here? And no jokes, okay, I don't need to be reminded that I've been dumped thirty—forty—thirty? Oh god." She looks down into her empty carton with such remorse that Sheldon is driven to remove the tequila from the vee of her legs.
After a moment of consideration, he applies the tequila to his own ice cream. Liberally.
It makes Penny laugh.
He makes Penny laugh.
"It's gonna be fine, okay?" Penny says. "Leonard and I will go back to being friends, and you and Amy—well, god only knows with you and Amy, maybe you'll manage to be friends or maybe you'll be one of those weird couples who is super awkward and pretends they aren't or maybe you'll hate each other or maybe one of you will build a time machine and travel back in time and make it so you were never in a relationship, oh my god, Sheldon, if you built a time machine you have to let me borrow it."
Sheldon's first bite of his ice cream cocktail is biting; after he chokes it down, he feels queasy. "If I build a time machine," he says, "I feel it would be irresponsible to let anyone use it. We can't know what the repercussions of changing the timeline would be."
"Liar," says Penny. "Hey, pass the tequila."
He passes her the tequila. She empties it into her empty carton and says, "Whoops. Didn't think that one through."
"Penny, I'm perfectly serious," he says. (Tequila is alcohol, alcohol a disinfectant. He can share disinfectants, it won't kill him.) "I might change it so I'd never been born—or so Leonard Nimoy had never been born, can you imagine? The smallest interference could have catastrophic consequences."
"Liar," she says again. "You aren't perfectly anything." (Sheldon takes offense at this, but Amy liked to point out that the better part of valor was discretion. Instead of voicing his offense, he takes another bite of his chocolate tequila frozen cream.)
Sheldon seizes that moment to contemplate his failures, both personal and professional. As a man he is not given to (humility) denial of his talents, but even the hardiest of egos is forced to reconsider when he has crashed through so many opportunities with such public and enthusiastic self-destruction. It started when the discovered the new element through error—or, no, perhaps when he lost the esteem of the NSF after that fiasco in the Arctic, 'existence of monopoles' indeed—or earlier, when the government took away his yellowcake uranium—
And Sheldon thinks about how these effects were caused not by the men in black, by his traitorous friends, by the imbeciles who continued to applaud him for a simple numeric mistake, he thinks about how these effects and more like them have only one common trait: Sheldon himself. His wrongdoings are caused by his own limitations as a scientist and as a human being, and now he feels like even more of a waste, like a glory-seeker who squandered all the promise of that little boy from Texas who would sit beneath the eaves of his grandmother's house and watch the stars...
"Whoa, buddy, are you crying?"
"No!" Sheldon says, bolting upright. "I am most certainly not—" He has to break off to sniffle.
"Sheldon, you're totally crying! I didn't even know you had tear ducts—sorry, that was mean." She holds up the empty tequila bottle and gives it a little shake, a little See? Not my fault. "Sorry, sometimes I forget what a lightweight you are. I don't think I've ever seen tequila make someone cry, though."
"There is," Sheldon says, with what he feels is impressive dignity, "a dust mote. In my eye."
"Sure, sweetie. Sure there is. Ready to use that time machine yet?"
"1985," Sheldon says.
"Yeah? What's so great about 1985?"
"I had not yet begun to think," Sheldon says.
"And what if you change something?" Penny says. "Thought you were too noble for time travel. What if you screw up and...oh, I don't know...we all wake up with fish heads?"
"You won't be upset. As far as you'll be aware, you'll always have had a fish head. Really, Penny." He tuts at her.
"What if you change something else by accident?"
She shrugs, slumps further down on her couch cushions. "You could make it so George Lucas never made those, you know. Those other movies with Ewan MacGregor."
"I could. I could prevent Kripke from ever being born," he says, slowly, savoring the taste of that thought. "I could kill everyone who ever bullied me before they were born. I could stop my father from—I could stop my father."
"You could kill Hitler!"
"I could kill J.J. Abrams," he says, with real feeling.
"Oh Christ, you aren't still pissed about that, are you? Star Trek whatever was not a crime against humanity."
Sheldon suspects the new feeling welling up in him is petulance. "I could make it a crime against humanity," he says. "I could travel back in time and make myself the first president and then set the national legal stance on reboots. DC would be almost completely unrecognizable, though," he adds.
"You could make it so Kurt never steals my TV."
"I could. I could make it so you never meet Kurt."
"You could make it so I never meet Leonard," Penny breathes. "Can you imagine? Boom. No more exes ever again."
"I only have one ex," Sheldon says, sadly. His tequila has bled even more thoroughly into his melting ice cream, so the carton between his knees holds only a murky liquid that smells almost sickeningly sweet. A less inebriated Sheldon would be appalled to have his feet on Penny's coffee table.
"Yeah. Yeah, no. Hey, did you ever wonder what would happen if I'd never gone out with Leonard and you'd never hooked up with Amy? Uh, dated. I mean...dated."
"Go on," Sheldon says.
"It's just—I could be way off-base here, but I kind of thought you and I were...that things were heading...that, you know."
"That our friendship was progressing in a less friendly direction," Penny tries.
"You're suggesting that we might have become archenemies?"
"No, sweetie. Just—forget it."
At that moment, either the revelatory powers of tequila or Amy's careful coaching on primate courtship rituals makes itself known.
"Oh," Sheldon says—
—and he leans over—
—and kisses Penny, right on the mouth.
"What the fuck was that!" Penny squeals.
Sheldon regards her solemnly. "I believe it was the tequila," he says, and then he leans past her and vomits in chocolate technicolor all over her rug.
Penny gags in sympathy, claps her hands over her mouth, breathes loudly through her nose.
Pats him on the cheek.
Says, "It would never work out between us anyway."
Sheldon accepts her challenge.
He spends days one through three of his campaign giving her apartment the thorough cleaning it so sorely needs. Her rug still smells, if faintly, of vomit; Sheldon himself woke in the much the same state, albeit with a headache and the lingering memory of being told he couldn't have something. He hydrates, takes the recommended dose of Aspirin, and showers twice. Penny's rug doesn't fit in the shower, but he has a nice store-brand aerosol cleaner and the same powerful sense of smell and primal devotion to cleanliness as Felis catus, the common housecat, which Sheldon has always respected as a paragon of virtue.
Penny works around him—sorting her mail, getting ready for work, getting ready for bed, watching TV in the evenings. She asks Sheldon not to vacuum while she's home. She asks Sheldon what he wants for dinner, and brings home two orders of Thai food. She asks Sheldon an impossible number of questions, and he answers what he can during the quieter moments of scrubbing her bathroom grout.
She does not ask why he invited himself to clean her home. His presence has been accepted, his habits accommodated in this one small way without fuss; in thanks, he arranges her shoes by color rather than by his preferred method of function and style.
On the fourth day, he escorts her to the Cheesecake Factory, his efforts at mannerliness only briefly dampened when he realizes that since she drove him, he'll have to walk home or wait for the end of her shift. He spends the next five hours browsing job classifieds for her on his phone, and the hour after that checking over Penny's homework. "Don't give me the answers, okay? Just...circle the stuff that's wrong, and I'll work it out myself."
"Penny. I think I know how to grade homework."
"Sheldon. I think you don't even know what you don't know."
"That's—what kind of impossible riddle is that? Of course I don't know what I don't know. It's self-evident."
"Whatever, sweetie," she says, but the next time he sees her, she brings him a Diet Cuba Libre on the house.
On day five, when he meets her at the complex door and holds it open for her, she says, "Thanks, Sheldon. Boy, you really do miss Amy, huh?"
"No," Sheldon says. Preposterous thought. He doesn't miss Amy. He occasionally performs his Amy-rituals, dressing in the shirt and slacks she'd bought him, cleaning his hands with the extra-strength sanitizer she kept in her lab, but Penny predates any association with Amy. Penny is projecting her own loss of Amy, perhaps, but Sheldon feels more that the steam engine of his life, after a short diversion through an unfamiliar land, has reverted to its original tracks.
Upon further prodding from Penny, he admits that Amy had become familiar to him and that, in her absence, he felt a disruption that might express itself as missing her—but, he explained, he also valued the time spent with Penny for her own sake, and if Penny would consent to drive him to Radio Shack—
"Ughhh, fine, just let me put these groceries away," Penny says.
"Wouldn't you be more comfortable if you let me do that?" Sheldon says, pointedly. Penny acquiesces; Sheldon arranges her groceries, fetches his jacket, and meets her at the top of the stairs.
"Someday we're getting you a windbreaker that doesn't make you look like an old man," Penny says. "C'mon, race you down!" She thunders away. Sheldon, dumbfounded, bolts to catch up, and by the second floor has regained enough of his breath to defend his jacket (comfortable, possessed of the necessary number of pockets, colored in a pleasingly neutral scheme).
At Radio Shack, he buys a clapper for the fairy lights strung up in her bedroom. He doesn't tell her it's there; she must discover it by accident, because when he delivers a fresh carton of creamer to her kitchen the next morning, he hears her clap twice before she emerges.
When she sees the creamer, she brushes a kiss over his cheek—close enough he can feel her breath, but careful not to touch her lips to his skin.
He leaves a comic book he thinks she'd like on her nightstand.
He rides in her car without upbraiding her driving.
He tells the the Wi-Fi password without prompting.
Penny spends days twelve through fourteen eyeing him suspiciously, avoids him on days fifteen and sixteen, holds a hurried conference in whispers with Leonard on day seventeen, and appears to accept his new behavior as "just another weird Sheldon thing" by day eighteen. On days nineteen through fifty-six, she acts within the normal parameters set by precedent. On day fifty-seven, he finds her waiting in the lobby, jiggling her keys impatiently as she shifts the packages in her arms.
"Mind taking a few of these?" she says. "It's new-shoe Thursday."
"Must I?" Sheldon says, but he takes two bags and a box from her. Fair trade; last week she helped him pack, carry, and transport three of his older model train sets to a second-hand hobby store.
On day sixty-three, rather than simply leaving the creamer, he joins her for breakfast.
On day seventy-seven, they receive the first of a continuing series of postcards from Amy, who has found the tropics don't hold enough excitement for her liking and who has moved on to Siberia.
On day ninety-eight, she doesn't laugh at him when he painstakingly separates his Skittles by color before eating them.
On day ninety-nine, she says, "Sheldon, look, I—make sure this isn't just because you miss Amy, okay? Just...make sure."
On day one-hundred twenty, he attends the opening night of her latest production, claps in the appropriate places, bites back a scathing remark when his seatmate coughs without covering his mouth. He brings Penny flowers, but the plastic kind—daisies. She thanks him and listens to a short lecture on daisy cultivation without protest.
On day three-hundred eighty-one, she asks him out on a date. Two weeks later, she proposes. Sheldon accepts, with the caveat that he'll be in charge of writing their vows.
On day five hundred, they marry; on eight-hundred sixty-five, they celebrate their first anniversary. Amy sends them a scale model of the TARDIS and a football signed by the '95 Cornhuskers; Penny drinks tequila out of the bottle and coaxes Sheldon into sharing.
They move into a house. Sheldon relocates his point of origin. A cat adopts them. Penny runs through a succession of jobs until she lands a spot as a radio host. Sheldon and Wil Wheaton start another web show, this one far more successful than previous efforts, if less enlightening on the topic of flags. CalTech offers Sheldon tenure; he accepts, and Penny takes him out dancing and then to a midnight premiere of Star Trek XV in celebration.
They grow into each other. They talk about children, they drive each other up the wall, they fight and make up and make out and make each other laugh, they tack Amy's postcards up on their refrigerator, they go to the comic book store on Wednesday and to high-school football games on Friday nights—