Everfree Forest, October 9
11:58 PM — 3 hours after the Fracture in Time
“You did something,” Serene said flatly. “What?”
Starlight took a step back. “I-I don’t know wh-”
“Yeah, you do,” growled Serene. “I don’t know how, but-” She rubbed her head. “I’m seeing things. I’m remembering things that never happened. I… I remember capturing you, plain as day. You-” She pointed at Sunburst, who twitched and backed up. “-had an arrow sticking out of you leg. But…” She shook her head and glared at Starlight. “Something happened. Right now, everything that’s happening is happening because of you or me. It wasn’t me. So it was you. I’ve been dilating time for hours to search this blasted forest and find you. Because I need to know: What. Did. You. Do?”
Starlight’s mind raced for half a moment before she realized nothing she could come up with would be convincing. Of course, knowing Serene, the truth probably wouldn’t be convincing either. “I went back in time and changed the past.”
Serene stared at her for a moment before getting overtaken by the shakes. It looked like she was laughing silently. “No,” she said softly, “no, no, no. That’s impossible, you ca-”
“You told me this already,” said Starlight. “You told me about the filly.”
Serene froze. Her jaw dropped a little. She blinked. Twice. Thrice. Then she whispered, “The filly?”
Starlight nodded. “With the carriage. Hearth’s Warming.”
Serene blinked again. Her eyes were distant, as if her mind was a million miles away. “I…” she muttered. “I never… I’d know, I…” Her eyes narrowed. “How?” she asked. “How’d you do it?”
“Star Swirl’s time travel spell. I used it, I came back to a point where I hadn’t been before, kept you from capturing us. Then it ran out, and I… I sorta…”
“She’s both future Starlight,” said Sunburst, “and present Starlight at the same time. A living quantum superposition. Maybe. I think. It’s, I don’t know.”
Serene blinked yet again, then started pacing. “How?” she growled. “How did I miss this? This shouldn’t be possible.”
“I don’t know either,” said Starlight. And if she was being honest with herself, if she hadn’t seen herself change time all those moons ago, she probably wouldn’t have tried it. But Serene didn’t need to know that. “Maybe… maybe it’s because the method of time travel is different?”
“That shouldn’t have mattered,” said Serene, “because the Neigher-Joy field can’t interfere with itself, an-”
“THAT’S IT!”
Starlight and Serene looked at Sunburst. He had the largest grin possible painted on his face and he looked like he was about to explode.
“What’s it, Sunny?” asked Serene quietly. “Small words, remember.”
“Okay, okay,” said Sunburst, pushing his glasses up, “it’s, this is, this is good. Real good.” He clapped his front hooves together. “Why can’t time paradoxes happen?”
Serene rolled her eyes. “Because the Neigher-Joy field can’t interfere with itself. Like I’ve been saying.”
“Right, right. Now, what’s special about, about you and Starlight?”
“We got dosed with chronon radiation.”
“Which meeeeaaaans…”
Serene scowled and cocked her head. “Sunny, I’m in no mood for this. Spit it out.”
“Sorry,” Sunburst said quickly, taking a step back. “It’s just, I thought, sorry.” He swallowed. “Which means that you and Starlight aren’t in the Neigher-Joy field.” He pointed at Starlight. “When she went back in time just now, she was only using her own magic, so the Neigher-Joy field had nothing to do with her return. She could, she could do whatever she wanted without having to worry about paradoxes because the, uh, the Neigher-Joy field wasn’t interfering with itself. She couldn’t change things earlier, at, at the core, you couldn’t change things, because your going back then was, it was dependent on the time machine core, which was in the Neigher-Joy field. But since Starlight’s magic, it comes from her, and she’s not in the, in the Neigher-Joy field, so it…”
Starlight got the gist and began tuning Sunburst out. That… that actually made sense. A lot of it. She and Serene were the only chronon-active ponies in the world, after all, and Serene wasn’t a unicorn. She was the only pony in the world in a position to change the timeline, and this was the first time she’d thought about it. Serene probably would’ve ignored magical versions of time travel because of her experience studying it in Project Promenade, so the idea never would’ve come up.
Starlight examined Serene. She looked some combination of confused and thoughtful. Like she’d realized the implications of everything and was following them to a conclusion. Starlight wasn’t sure whether that was a good thing or a bad thing. They were technically on the same side — they both wanted to close the Fracture — but their methods couldn’t be more opposed to each other.
Sunburst was still talking. “-and Star Swirl’s spell works by temporarily displacing you in the Neigher-Joy field, but, but you come back because your point of origin, it, it yanks you back when the magic runs out. But Starlight changed time, so she didn’t have a point of origin, not anymore, so she decohered when the magic ran out instead of going back, and, and due to what I think are quantum effects similar to entanglement, she merged with the version from the changed timeline, and-”
Serene suddenly coughed. “Starlight… why’d you come here?”
“Huh?” asked Starlight. “Well, I, I wanted to make sure Sunburst and I were safe, so-”
“That’s not what I meant. You came back certain you could change things,” whispered Serene, “and you DIDN’T TRY TO FIX THE FRACTURE THAT CAUSED THIS MESS IN THE FIRST PLACE?” She slapped Starlight in the face, too fast for her to dodge. “Idiot,” she growled.
“Sorry!” yelped Starlight, taking a step back. “I wasn’t thinking! I just-”
“You weren’t thinking.” Serene rolled her eyes. “Well, of course you weren’t, why should you start then?”
Starlight switched gears, folded her ears back, and took a step forward. “Look,” she snapped, “I’d already tried that and it didn’t work.”
“Yeah, and because Star Swirl’s spell is one-time use, you just ruined our best chance at fixing this mess. Way to go, Starry! You real-”
“Um…” Sunburst coughed. “Actually, I think…” He looked away. “It, it’s stupid,” he muttered, “but…”
“Sunburst,” Starlight began.
Sunburst started talking again before she could say anything more. “Technically, yes. Starlight, she has used Star Swirl’s spell. But if she’s in a, a quantum superposition of a version of herself that hasn’t, she also hasn’t used the spell at the same time. She… Hypothetically, she, she might be able to use it again. Maybe. Possibly. I don’t know.” He grinned halfheartedly and looked away again.
Starlight and Serene stared at Sunburst. Starlight blinked. “What?”
“Gah!” Sunburst threw up his hooves. “Starlight. Let’s just assume you’re in a quantum superposition. You are two versions of yourself at the same time. You used the time travel spell, yes. But that’s just one version. The other version didn’t. At the same time, you did not use the time travel spell. You both did and didn’t. But the didn’t means you still can. In short: you can use the spell again.” He dropped to his rump and crossed his forelegs, scowling at the two of them. “That make sense?”
Starlight had barely given it any thought (except that, yes, that explanation did make sense) when Serene whipped her head towards her. “Do it.”
“W-what?”
“Do it!” yelled Serene. “Take us back! We have a one-in-a-million chance to fix the Fracture before it happens, and you’re just standing around with that moronic look on your face!”
“Serene, don’t you think-”
“I’ve been thinking for seven years, Starry! Seven years, I’ve been thinking about this! The one thing that always comes up is that if I could stop the Fracture from starting, I would!”
“Well, it’s- I don’t know-”
“You’ve already tried it! It didn’t work then because things were different then! Please! I just want to end this stupid thing and the one pony who can do anything about it is sitting there hemming and hawing and I want to-” Serene cut herself short and glared fiercely at Starlight. “You don’t want to know.”
“She, she’s got a point,” mumbled Sunburst. “There’s really no reason to not do it now. Might as well just, just get it over with, you know?”
Starlight didn’t know. Everything was happening too fast, and she wanted some time to just think. But Serene was glaring at her, nostrils flared, with an “I don’t want to wait a single second longer” face. Trying to stall for a little, Starlight grabbed at the last straw. “But what if we try to change things and it doesn’t work? I mean-”
“We’ll still have changed the, changed the past,” said Sunburst, pushing his glasses up his muzzle, “so you’ll still decohere, and you’ll still be in a superposition with a version of yourself who hasn’t, hasn’t used the spell, so we’ll just go back a little further and try again.”
And, of course, there was an incredibly simple reason why that wouldn’t work. But Starlight had suspected there would be, and she’d mostly used the time to assemble her thoughts on going back.
Yeah. Might as well do it now. She’d heard the idea, she suspected it would work, and there was pretty much no way she was not going to do it eventually. Sunburst’s explanation had even said she could try again if she failed. “Fine,” she said. “Let’s do it. Right now. Failsafe room at the time of the Fracture. We’ll talk you out of breaking the machine.”
Serene grinned a devil-may-care grin, and for an instant, Starlight was reminded of the original Serene. “Alright,” she said. “You coming with us, Sunny?”
“Well, it’s, I might as well,” said Sunburst, batting at his ear. “It, it’ll help your past self to not do things if, if I’m there, too, probably.”
“Nice. Let’s go. Hooves crossed, amIright?”
She was definitely right. Starlight called on her magic again, trying to bring forth the spell. For a single second, she was terrified it wouldn’t work, that Sunburst had been wrong.
Then the spell clicked and they were gone.
Streamhaven University, October 9
8:12 PM — 5 minutes until the Fracture in Time
“-while ‘time apocalypse’,” said the Doctor, “is a bit vague as to the… the, um…”
The spell deposited Starlight, Serene, and Sunburst right in the middle of the failsafe room. Starlight remembered the Doctor’s little speech; this was right before Serene — Past Serene — entered the failsafe room and broke the time machine. As the trio gathered themselves up, they stared at Past Starlight and the Doctor, who stared back.
Nopony said anything for a moment. Then the Doctor coughed and muttered, “This is a new one.”
Serene smiled, one of the more genuine smiles Starlight had seen on her since the whole thing started. “Hi there! We’re gonna save the world.”
“That’s, um, that’s what we’re doing,” said Past Starlight.
“It won’t work,” Serene said, waving a hoof. “You’re doing it wrong.”
Past Starlight’s eyes narrowed. “And just how are-”
The door opened, and in walked Past Serene and the Monarch soldier. Past Serene actually tripped when she saw who was in the room. She looked between everypony, slightly agape. “Just what in-”
“Listen,” Serene said calmly, stepping forward, “you don’t want to do this.”
Past Serene blinked. “But… but this…” She looked around the room. “This is…”
“I’m from the future.” Serene grinned. “You don’t want to do this. It’ll keep the Fracture from happening.”
“Even-”
“Yes, even in spite of everything you’ve done and seen.”
“There’s a variable that, that you didn’t account for,” said Sunburst. “Magical time travel and mechanical time travel, they, they work differently.”
“But…” Past Serene chewed her lip and looked back and forth between Serene and Sunburst. “You’re sure?”
Serene froze. Starlight could imagine what was going on in her head: technically, she wasn’t sure. She was just going on with a wing and a prayer. If she was wrong, Past Serene would… Starlight wasn’t sure what she would do, but it couldn’t be anything good. Serene was staking an awful lot on things going right if she said, “Yes.”
She still said, “Yes.”
Past Serene opened her mouth. Closed it. The Monarch soldier next to her shuffled his hooves. Past Starlight looked at Starlight in confusion. Starlight just shrugged and muttered to her, “It’ll all make sense eventually.” She didn’t add, Hopefully.
“Positive?” asked Past Serene.
A dim light, slowly glowing brighter, began shining around Starlight, Serene, and Sunburst. The spell was nearing its end.
“Of course,” said Serene.
“Trust us,” piped up Sunburst. “We’re from the future.”
“She already said that.” Still staring at the rack, Past Serene raised her hoof, then lowered it. Scowling, she said, “All right. But you better be right about this.”
“Of course I’m right,” said Serene as the light built up. “I’m the same as you, but smarter.”
The time spell collapsed.