NOTE: You guys know I don't own these characters. They are property of the creators of The Big Bang Theory. However, there will be a few characters that are my own creations interwoven throughout. Enjoy!

*The Compatibility Constant*
Chapter 1: The Parallel Possibility

"So you see, Amy, there's no way to go beyond a 10th dimension. That's all there can be… at least, so far as we understand it."

Sheldon was trying to explain the intricacies of string theory to Amy. While she grasped the basics of quantum physics, she was by no means an expert. She had dedicated her life to neurobiology.

Sheldon didn't care much for biology - so other than key updates in the advancements of the nicotine addiction study she had previously been involved with, Amy tried to avoid conversations about her own work. However, Sheldon could go on for hours about bosons and quarks… about space-time and the multiverse. She'd gladly let him jabber on, so long as they were spending time together.

"And Parallel universes are a key part of M-theory, which is sort of an encompassment of other versions of string," Sheldon continued.

If she was being completely honest, Amy did find his work fascinating. But she mostly just wanted to spend time with her boyfriend. It made him happy to go on and on. And if he was happy, she was happy. Amy leaned in towards Sheldon to show her interest.

Sheldon was comfortably seated in his spot; his hands waving as he attempted to help her visualize the expanse of the universe.

"In theory, there could be an infinite number of parallel universes. Which means that literally anything you can think of actually is happening in a parallel universe. There could be infinite numbers of you and me out there, Amy. Slightly different, of course, but there nonetheless."

Interesting, Amy thought to herself. So that means… in an alternate universe an alternate version of her could be dating an alternate version of Sheldon. The Amy and Sheldon in the parallel universe could be just like any normal love-struck couple in this universe. They would touch… hug… kiss.

Interesting, indeed. She was beginning to see string theory's appeal.

It was fun to think about, but she wouldn't trade what she had with this Sheldon in this moment for anything. Their relationship may not be conventional, and - sure - she wished that it was progressing a bit faster, but she knew what they had was real.

"See, Amy, isn't physics so much better than biology?" Sheldon nudged.

Amy smirked. "'Better' is a relative term, Sheldon. While I admit that physics - specifically string theory - is intriguing… biology is just as in-depth and has arguably more real-world application than an unproven theory that involves multiple universes and dimensions."

Sheldon let out an offended gasp, but didn't have time to retaliate. The moment was interrupted as his roommate walked through the door, followed closely by his own girlfriend.

Leonard smiled at Amy as he closed the door. Penny waved at them and made a beeline for the fridge to grab a bottle of water.

"Hi, Amy! I didn't know you would be over here. How has work been going?" Leonard asked.

"To be honest, it could be better," she frowned. She had been kicked off the addiction study after an unfortunate incident with one of the primates. She truly missed the project. Not to mention, she had already devoted so much time and energy to it that it felt like a big piece of her life had been stolen away.

"Oh, that's right," Leonard remembered. "Any new projects on the horizon?"

"Nothing yet," Amy replied.

Penny plopped down next to Amy on the couch and put a consoling arm around her.

"Oh, Ames, something good will come along soon, I'm sure of it!"

Amy couldn't help but smile at her bestie. Her optimism was contagious.

"Thanks you two."

Sheldon sighed and walked over to his computer, obviously annoyed that the focus had been shifted away from his work. The others ignored him, and Amy shifted into Sheldon's vacant spot to give Penny some more room on the couch.

"Well, I have some good news!" Penny exclaimed.

Amy was eager to grab onto anything to help lighten the mood, which had taken an abrupt nose-dive while discussing her work.

"What's that, bestie?"

"I got a part in another play!"

"Really?! That's amazing! What's the part?"

"She's going to be Maggie from Cat on a Hot Tin Roof!" Leonard interrupted. Penny glared at Leonard for stealing her opportunity to deliver the news herself. Leonard immediately wandered to the kitchen to avoid being hit by his girlfriend.

"Wow, Penny!" Amy exclaimed. Penny's good mood quickly returned when she noticed her friend's huge grin.

"Apparently, they saw my performance in A Streetcar Named Desire and thought I would be perfect for the part!"

"Well, that's no surprise. You were amazing in that play."

Amy glanced over at Sheldon - feverishly clicking away at his mouse. It looked like he was playing some kind of simulated city game.

"Sheldon - did you hear what Penny said? Aren't you going to congratulate her?"

"Of course I heard her, Amy. I hear everything." Sheldon paused his game and turned around in his chair. "But is it really Penny that deserves congratulating? She's merely doing her job. The people you should be congratulating are the casting managers who were able to recognize her talent. Penny is obviously a good actress, though her singing ability leaves a lot to be desired."

Penny's eyes began to tear up.

"I'm merely stating a fact, Penny. No need to get emotional." Sheldon rolled his eyes and returned to the game.

Penny and Amy exchanged their own eye rolls, but both knew that even though Sheldon's compliment was buried inside of a somewhat-insult, it meant a lot coming from him.

Standing up, Amy reached down and gave her friend a huge hug.

"You'll do great," Amy said. "Be sure to save me a ticket for opening night."

"Of course! Are you leaving?"

"Yes. I need to get home and do some laundry."

Sheldon paused his game again and turned back around. "You're going home?"

"Yes, Sheldon. I've been here for hours. You of all people know the importance of laundry night."

Sheldon gave an understanding nod, but Amy noted a hint of dejection in his eyes.

"Very well," Sheldon said. "I'll talk to you tomorrow and give you the details of our date night." He turned back to his computer game.

Amy smiled and waved at Leonard and Penny before heading out the door.

As she scaled down the four flights of stairs to the lobby, Amy pondered her boyfriend. Despite his obvious social awkwardness, he had moments of true - albeit typically accidental - sensitivity. Unfortunately, they were often masked by his inability to pick up on social cues, and his habit of coming off to the unknowing onlooker as, well, an ass.

I can't fault him for his idiosyncrasies, she thought. They're what make him special. After all, not too long ago Amy had a very similar attitude. Over the past couple years, though, she had opened herself up to her friends, and they had helped her slowly break out of her shell. She knew she still had a ways to go, but she was becoming increasingly comfortable in social situations, and had over the past few months really begun feeling an urge to move forward in her relationship with Sheldon.

Of course, Sheldon had to be ready to progress too, and he had yet to put even a tiny hole in his shell… though, he was getting closer every day. He was softly tapping away at it, and Amy knew the shell would eventually crack.

This is when a parallel universe Sheldon would make it so much easier, Amy laughed to herself.

Chapter two coming soon!

Notes: This is my first fan-fic, so I am very open to reviews and constructive criticism. Thank you in advance!

Also, please note that I am by no means a physicist OR a biologist. I have a very limited understanding of string theory, so if it's not entirely accurate – I apologize. I will do my best with my basic knowledge of the field whenever it appears in this story. :o)