Quantum Starlight

by Rambling Writer


12 - Ouroboros Vomit

Everfree Forest, October 9
11:46 PM — 3 hours after the Fracture in Time

Starlight tripped. Which was quite impressive, considering she was traveling through a void where time and space were essentially meaningless.

“Starlight!” Sunburst hissed. “Come on!” Which was also quite impressive, considering he wasn’t traveling through said void.

As she lay there on the ground (which was equally impressive), the idea that something wasn’t right ran through Starlight’s head. Sho-

“Come on!” Sunburst lightly kicked her in the head. “What’s with you?”

Starlight slowly got to her feet. She wasn’t back in the medical ward or in whatever not-place she travelled through when travelling through time. She was in the Everfree, right next to the Doctor’s lab, and from the sounds of things, it was right after she’d seen herself come back and-

Wait. Seen herself come back? She’d been the one who came back.

Sunburst smacked her again. “Starlight, you, you’re looking weird all of a sudden. We, we’ve gotta move.” He flicked his tail and trotted off, sticking to the wall of the building.

Starlight followed (vaguely noting that they were traveling much faster than they had when Sunburst’s leg was busted), but her mind was a million miles away. She thought back, combing through her memories. Something was wrong. How had she gotten here? A few seconds ago, she’d started walking. Okay. Before that, she’d tripped. Okay. Before that, her future self had-

No. That was wrong. She’d been the one to come back, not the one here, right? She thought back further. Yes, she remembered being in the medical ward with Sunburst, talking about going back. She thought forward a bit. She’d gone back in time. Okay. She’d stopped that soldier. Okay. She’d told herself and Sunburst to avoid Monarch. Okay. The time travel spell had ended. Okay. She’d tripped. Okay.

No, wait, not okay. She distinctly remembered her being here from two perspectives. She thought back again, focusing on the specific memories, and-

She had two different sets of memories from the last minute. One from the Starlight who hadn’t time travelled, and one from the one who had. That was weird enough, but the really weird thing was that they were both perfectly clear. One wasn’t trying to “overtake” or “crowd out” the other. It was like she both simultaneously.

Somehow, this was making her head hurt more than any other time travel shenanigans.

After a few moments of trotting through the forest, Sunburst looked back over his shoulder and frowned. “Something’s up,” he said. “What is it?”

Starlight opened her mouth to tell Sunburst. No, wait, he’d think she was being weird. She closed it. No, wait, he deserved to know. She opened it. No, wait, he’d th- Starlight started talking before her brain caught up with her mouth. “Sunburst, I… I just went back in time and saved us.”

“And… and what’s the problem with that? You’ve already traveled through time with magic.”

“No, I mean I went back.”

Sunburst cocked his head. “Yyyyyeah, that’s what I said.”

“No! It’s…” Starlight kneaded her forehead. “This version of me went back in time. I remember it happening from the perspective of the one going back.”

“Ooooooooh.” Then Sunburst blinked and frowned. “Wait, what? But-”

“I know. And… this isn’t the way it happened the first time.”

Sunburst blinked again and stumbled on a log. “Uh… what? Starlight, y-”

“Last time,” said Starlight, “I never came back. That soldier shot you in the leg. We got captured by Serene — she’s the founder of Monarch — a-”

Serene’s the FOUNDER of Monarch?

Starlight sighed. “Let me start at the beginning.”

As the two of them walked through the Everfree, Starlight told Sunburst everything. Their capture by Monarch. Their imprisonment in the Monarch building. Serene’s involvement in everything. Her decision to go back. Her arrival at now.

“…and I thought the time spell would just take me back to when I left in the changed future,” she finished, “not leave me… here.”

“Huh.” Sunburst cocked his head and flicked his ears. “That’s, that’s rea-”

Mid-sentence, a thought hit Starlight like a ton of bricks and her blood ran cold. “What happened to the future?” she whispered. “My old present? Did I just kill them all?”

“Well, no, you,” said Sunburst, “they don’t exist yet. The future hasn’t happened, so-”

“We’re in the middle of a fiasco involving time travel, and you’re saying the future hasn’t happened yet?”

“Well, okay,” said Sunburst, pushing up his glasses, “it, it’s more complicated than just plain death. Those ponies, they, they will exist eventually, just, you know, different versions of them.”

“But what about the ones I talked to? Those versions? What about the me in the past I… I replaced or merged with or whatever?”

Sunburst sighed. “Starlight. You changed the timeline. Yes, versions of, of ponies are gone. But those particular ponies are still alive, just, just not those specific iterations. You can’t do anything about it. So stop worrying. Please. You’ll just drive yourself crazy.”

Starlight flicked her ears and stared at the ground. Easy for him to say. He hadn’t been there. He hadn’t talked to somepony who knew things from a timeline that didn’t exist anymore. If he’d seen the timeline, he’d see things differently, Starlight was certain. It was kind of hard to judge him, though; this was an incredibly abstract concept. Honestly, she was having trouble believing it herself, and she had seen it.

“Oh, and the term’s quantum suicide.”

Starlight looked up. “What?”

“When the effects of, of quantum theory, particularly within the, uh, the many-worlds interpretation, cause an alternate version of yourself to die while you survive, it’s, it’s called quantum suicide. And you, your continued survival is quantum immortality.”

Starlight blinked. “Scientists already have a term for that? Just wh-”

Sunburst laughed nervously and pushed his glasses up. “W-well, not in the way you’re thinking. See, it’s, it’s from a thought experiment, and- You’ve heard of Haflinger’s Cat, right? Cat’s both alive and dead until you open the box?”

“Yeah?”

“Okay, so there’s a fifty percent chance the cat’s alive once you open the box. Now do it again with the same cat. The probability that the cat will survive both is only twenty-five percent, because they’re independent events, and the odds of both is fifty percent, and when you mul-”

“Sunburst. I don’t need an education in probability theory.”

“Hem. Right. Now, the probability that the cat keeps surviving keeps, it keeps dropping. Specifically, the probability of the cat surviving n boxes is one over two to the nth power, be-”

Sunburst!” yelled Starlight.

“Sorry, sorry. Now, that’s true for a single universe.” Sunburst suddenly broke out in a massive grin. “BUUUUUUUUUUT…”

He paused for effect. Starlight let him have it. Sunburst sometimes liked to go dramatic with his explanations.

“But if you assume the many-worlds interpretation is correct,” said Sunburst, not dropping his grin, “then there absolutely must be a universe out there where the cat survives every single box it’s put into, because there is always a chance, no matter how slim, of the cat surviving.” He wiggled a hoof at Starlight. “That cat that always survives? It has quantum immortality. And when one of its other versions dies, it undergoes quantum suicide.”

“So… so when the time spell collapsed, and I stayed here…” Starlight stared at where she’d come out. “Did I commit quantum suicide?”

“Well, no. Not exactly. It’s, I don’t think so. You can remember you saving me from a perspective that isn’t you saving me, right?”

“Yeah.”

“Then you might be in, uh, be in a quantum superposition of the two different timelines. I don’t know, we’ll have to get the Doctor’s opinion.”

“A quantum what?”

Sunburst groaned. “Sun and stars, I never thought I’d miss undergrads. Sorry, it’s, I forget you don’t know these things. Basically, you, you’re both the come-from-future Starlight and already-in-present Starlight at the same time.”

“How’s that possible?”

“Because of quantum.”

Starlight raised an eyebrow.

“Quantum physics is weird, Starlight,” said Sunburst defensively. “It’s hard to explain this if, if you’ve never taken a single course on it. Trust me, when you study it, it, it all makes sense. Usually.”

“I’ll take your word for it.” Starlight and Sunburst walked through the forest for a few more moments before she asked, “So… every time a crossbow bolt missed my head by a millimeter… did some other version of me die?”

“Oh, sure,” Sunburst said with far too much nonchalance. “If there was a, a chance of you dying, then yeah, definitely. In the many-worlds interpretation, anyway.”

Starlight’s voice was very quiet as she said, “…Oh.” All of a sudden, luck looked like some kind of sick joke. She might’ve lived, but only because nine other versions of herself died in alternate timelines. Super. Just plain super.

Sunburst picked up on it. “Don’t, don’t worry about it, Starlight,” he said. “It, that sort of thing happens all the time.”

The bottom dropped out of Starlight’s stomach. “What?

“Well, it has to,” Sunburst replied, still sounding way too calm. “I mean, if, if there’s a chance, no matter how tiny, that, that a meteor will fall from the sky and, and squish us flat-” (Starlight looked up purely on reflex and tensed, ready to cover her head.) “-then, in some timeline, it, it will.”

“So,” Starlight said slowly, “you’re saying that, that no matter what I do, some alternate-timeline me is going to die?”

“Yeah.” Sunburst looked over his shoulder and smiled. “Doesn’t that make you feel better?”

“…No, Sunburst, somehow, the fact that my mere continued existence may be constantly killing off versions of myself in alternate universes is NOT making things any better.”

Sunburst just shrugged. “Then go with the Clopenhagen interpretation. No alternate universes. Or at least, at least not from quantum physics. Clean slate and no quantum suicides.”

Starlight snorted. She still didn’t like the idea of it.

The two of them continued through the forest for a little while longer before Sunburst coughed and said, “S-so, um, now what? It, it sounds like we weren’t in that bad of a position back there.”

“Not really,” admitted Starlight, “but now we’ve got leverage. If we get to the Doctor, maybe we can make a plan of some kind and show that plan to Serene. Then once she knows we’ll have something that can work, she’ll probably let us go and use the thing when the time comes.”

“There, there’s more ‘maybes’ and ‘probablies’ in there then I’m comfortable with.”

“At the very least, we’re not prisoners.”

Sunburst nodded. “True.”

But really, Starlight was running in the dark. Metaphorically and literally. She’d only come back because she didn’t like being pinched, but now that she wasn’t being pinched, she didn’t have any idea of what to do. Only a vague hope that Sunburst and the Doctor could work together and find something. Although, if they contacted Serene of their own free will, then maybe…

Sunburst spoke up again. “You think the Doctor’s got a way to fix things?”

“Probably. He was talking about giving the Neigher-Joy field with lots of chronons, and wasn’t that what you were suggesting? So I figure that if two smart ponies each come up with the same idea on their own, they’ve gotta be on the right path.”

“It’s, it’s not like we’ll just have a plan the moment we get there.”

“Of course not. But it’s on the way, right? Yeah, I know it’s only like one percent, but it’s one percent further than we were before. Besi-”

There was no warning. No pressure, no headaches, nothing. In a rush of wind, Serene suddenly appeared out of thin air in front of them. She was breathing heavily and her clothes were riddled with tiny tears, as if she’d been galloping heavily through the forest for hours. Dirt stained her all over, and she was staring at Starlight and Sunburst with something resembling both rage and fear. “What. Did. You. Do?” she hissed.

Starlight was suddenly aware of how loudly she and Sunburst had been talking.