So, this chapter may be a little confusing, but I think it was getting necessary for me to explain some things.

Let me point out that this is by no means the only theory involving time travel, or even the correct one (or maybe it is...I don't know), but it is the theory used on the show, so that's what we're going with here.

Enjoy! And please review! (But please don't gripe at me about what an idiot I am. I'm not a scientists, guys.)

OoOoOoOoOoOoOoO

The days went by slowly, and Jade O'Neill began worming her way, little by little, into the hearts of the SGC personnel. Of course, Jack and Sam were both won over after the first couple of days, and it wasn't an uncommon sight to see the three of them sitting together in the mess hall, talking and laughing as if they'd been together for years.

General Hammond kept Jade restricted to her quarters, only allowed out with an escort, so when her parents were busy, Teal'c or Daniel would come down to visit with her. Teal'c took her to the gym and began teaching her a few basic lok'nel moves, which she picked up quickly. He was so pleased with her eagerness to learn that he was moved to tell Jack, "In time, your daughter will become a skilled warrior, O'Neill."

Jack replied that he would prefer they not send her off into combat just yet, but Carter seemed delighted, remarking that she had always intended to make sure, if she had a daughter, that the girl was schooled in martial arts.

Daniel occasionally brought Jade down to his office, and she eagerly pored through the books on his shelf. He sometimes had to set his work aside, not able to resist the opportunity to explain his research to her as she thumbed through notebooks and sketches.

"She definitely didn't get that from me," Jack whispered to Sam one evening. They had peeked into Daniel's office to see him and Jade sitting cross-legged on the floor, Daniel gesturing wildly as the girl ran her fingers over a large map on the floor, both of them caught up in eager conversation and surrounded by stacks of books on South American mythology.

Jade saw Janet often also, as General Hammond had ordered frequent checkups. By the end of the first week, she began coming in "just for fun", calling herself Janet's intern and trying to find little ways to help out around the infirmary. Jack overheard one airman in the locker room bragging to his team member that he'd had his sprained wrist wrapped by "O'Neill's little girl".

Of course, Jade was far from perfect. Despite their common interests, she frequently lost her temper with Daniel, their arguments usually ending with Jade storming out of his office and demanding to be escorted back to her room. Daniel learned to be patient with her, since she always appeared in his doorway a short time later, tearfully apologizing for her behavior and, occasionally, her harsh language.

The General grew frustrated for a different reason, as the girl tended to sneak away from her escort and find herself in places that she was not allowed. He once found her in the control room, trying to convince Walter to let her announce the next incoming wormhole, and she disappeared several times from Jack's side to be found later in the mess hall, usually with a large slice of cake.

In spite of her faults, it was amazing the way the entire base seemed to fall in love with the girl. She made friends with the SG teams, the technicians, the nurses…she was even seen occasionally chatting with the janitor. Jack joked with Daniel that it was her impressive parentage that made her so popular, but the truth was, despite Sam's assurances that the girl was very much like her father, Jack didn't see very much of himself in Jade. She certainly had some of his looks, and she often used his expressions and mannerisms, but her intelligence, her eagerness to try new things, her friendliness and high spirits…these were all things that he attributed to her mother.

Carter had been hesitant about the girl at first, but the more time they spent together, the more Jack noticed her practically glowing whenever the two were together. He almost felt a little jealous. Up until now, he had inwardly prided himself in being the only one who could get her to smile that way. Still, it made him happy to see her happy, and he was usually content to sit and watch the two of them, almost able to pretend they were a real family.

One evening, before he went home for the day, Jack wandered into Sam's lab to find her typing hurriedly on her computer, her eyebrows furrowed in concentration. She saw him step into the room and smiled, finishing her notes and pushing her chair away from the desk.

"Hi, sir. I was just finishing up my report."

Jack nodded and fiddled with one of the strange devices on her desk, thinking a moment before he spoke.

"I have a question, Carter."

Sam settled forward in her chair and folded her hands beneath her chin.

"Okay."

Annoyed with the distance between them, Jack walked around to the other side of the desk and leaned up to sit on its edge.

"Well, I've been thinking." Sam raised her eyebrows at him, and Jack gave her a blank look.

"It does happen occasionally."

She just laughed and gestured for him to go on.

"I've been thinking about this whole…future thing. I mean, I won't pretend I understand it all, but if we do complete this mission, and we fix things up all nice and tidy for the future, then what happens to Jade?"

Sam looked surprised by his question. "What do you mean?"

Jack shrugged his shoulders. "I mean, what happens to her? If we've screwed things up as badly as you guys say we have, then she's not ever going to be born, right?"

"Well, sir," Sam replied with a thoughtful expression. "If you combine what we know of time travel with the laws of quantum physics, we get a better understanding of the possible results of-"

"Carter…"

She paused and gave a sheepish smile. "Sorry, sir. What, exactly, do you want to know?"

"Will she disappear or something if we change her future?" He blinked and shook his head. "Her past, I mean. Our future. Whatever. You know what I mean."

Sam grinned up at him. "No, sir, she won't disappear." Looking as if she'd had an idea, she reached across the desk and picked up a sheet of paper, slipping a pencil out of her pocket and gesturing for him to watch.

"Look. I'll show you."

Jack hopped off of the desk and leaned over her shoulder, trying to focus on something other than the smell of her hair and the nice view from his position above her.

She drew a line across the sheet of paper, with two stick figures together on the left, and one by itself on the right. "Here's our timeline. This is you and me, and that's Jade."

Jack took the pencil out of her hand and sketched a baseball cap on his figure, smiling proudly as Sam snatched the pencil back and continued, trying unsuccessfully to hold back a smile.

"Okay, so she comes back to our time…" Sam drew an arrow to indicate Jade's travelling through time. "…and ends up with us. Now, when the timeline is altered…" She drew a branch off of the first line, starting a separate, but connected, timeline beneath. "…then it, in effect, creates a parallel universe."

Jack squinted at the paper in front of him. "Okay," he said slowly.

"Okay," Carter repeated. "The point is, she was sent here." She tapped her pencil on the alternate timeline she'd drawn. "So the future she came from…" She tapped the first line. "…is no longer our future. Thus, it has no bearing on what happens in our universe, and we can't have any effect on it. Jade was still born there, so she'll still exist here."

She smiled brightly up at Jack, clearly pleased with her own explanation. Jack frowned and tried to concentrate.

"So…not going to disappear."

"No, sir." Sam replied, laughing quietly.

A sudden thought occurred to him, and Jack looked back down at the paper on the table.

"She can't go back."

Carter shook her head slowly.

"No, sir. She can't. Even if we had a way to send her to the future, it would no longer be her future."

This was a distressing thought to Jack, for more than one reason.

"We're not going to have her in our future, are we? As a baby, I mean."

He expected Sam to blush again, to give one of her nervous smiles and stare down at her feet. It was a bit surprising to him when she looked up and met his eyes, a sadness evident in hers.

"No, sir. We can't. At least, the odds make it nearly impossible."

It took a minute for Jack to understand. Carter glanced back down to the paper on her desk, and he leaned back, trying to think of a way to cheer her up.

"Oh, right," he finally replied. "Because we'd have to…you know…at the exact same time that the other us…well, you know…"

His awkwardness was enough to break the intensity of the moment, and Sam laughed, her blush returning. Jack couldn't help himself. He rubbed his hand over the back of his neck and gave her a grin.

"Of course, if she told us her birthday, we could just…you know…calculate it up and try as many times as-"

"Colonel…"

Sam gave him a warning glance, but Jack was pleased to see that there was amusement in her eyes. He decided not to push her any further, and he stepped away, running his fingers over the side of her desk as he headed towards the door.

"Either way, sir," Sam added, gathering her things to follow him out of the room. "We've got her now, and that's good enough for me."