Broken Symmetry

by Trick Question


What Are the Odds?

Scarcely ten minutes had passed before the door opened again. As before, there was no warning knock. I nearly jumped out of my pelt (not literally, of course).

It was Twilight Sparkle, but she still had her forelock tied up in the band. At first glance I thought it was Starlight Glimmer returning, but I quickly deduced that Starlight would have been spying on Twilight and would have noticed her wearing her mane that way. It still looked odd, and deep down I feared this was all some sort of a horrid psychological game to make fun of me. I had grown to trust Twilight, but after my encounter with Starlight I didn't know what to expect anymore.

"Moondancer? Is everything alright?" said Twilight. She walked right up next to the enormous hourglass and stood there, watching me from a distance.

"Read the cover of this book, please. It's important," I said, telekinetically tossing her the same book I'd used previously.

Twilight caught the book with her magic and furrowed her brow in apparent confusion as she brought it near. "Okay..." she said, and looked down at the book. Then I noticed something odd: she was pretending to look at the book, but she was actually staring into the hourglass. I realized she was probably watching me in the reflection of the glass. Was this still Starlight Glimmer, I wondered? Or was it just Twilight, acting suspiciously toward my own unusual behavior?

"Al-Risalah... oh wait, this is the Theologus Autodidactus," Twilight finally said. "I forgot I had a copy here. What's this about?"

Twilight's voice was passionate enough that it was clear she didn't have the spell up any longer. Internally, I breathed a sigh of relief.

"Starlight Glimmer was here," I said.

"What?! How did she get in?" asked Twilight, her jaw agape as she walked up to me.

"She disguised herself as you. Perfectly, I might add, including the hair tie you're using now, though at the time I thought she was just mocking me," I said, feeling a bit queasy about the idea. Why would Twilight choose to wear her mane like that? Was it an attempt to be psychosocially endearing to me? I continued, "She wanted to trick me into taking her to the lab and destroying it with her."

Twilight dropped the book on the table beside the sofa. "Well, that cinches it. We need to get you out of Canterlot tonight."

"Wait, what?" I said. "When did this become a plan?"

"I already went out and bought you a train ticket. After cancelling that emotion spell, I realized I didn't want you to be anywhere near the lab until I've short-circuited the system. That way there will be no chance whatsoever of you going back a day and dying," she said. "Here." She handed me a ticket. It was set to leave for Ponyville at midnight.

"What about all the research you were supposed to be doing?" I asked. "Did you come up with anything?"

"Yes, but it's not important right now. I'll walk you to the train, and we can talk along the way," she insisted. There was something rushed and anxious hiding in the timbre of her voice. I didn't know if this was really Twilight or not, but I knew I was being played.

"It's fine," I said. "You go back to the castle. I'll head to the train station after I finish here."

It was hard to see in the dim lighting, but Twilight's face paled. "Look, I really want to make sure..."

"Twilight, I need you to tell me what's going on. That is, if this is even really you," I said, frowning. "You're a terrible liar."

Twilight Sparkle froze for an extended moment, then sighed. "Damn. Still not buying it?" she asked, and with a flash of her horn, her wings had disappeared again, although I could still see a vague outline. She also seemed too thin to be Twilight, as I could see the outline of her ribcage in the dim lighting—she was clearly malnourished, possibly anemic. I was physically too close to prevent her from attacking me, so I decided to lay all of my cards on the table.

"It's obvious by now that you don't want to kill me. What's your deal, Starlight? Why don't you just tell us what you want?" I asked.

She took a deep breath. "Twilight won't listen to reason. She's making a terrible mistake. It would be dangerous for me to approach her, but she'll listen to you."

"Okay. So why should I believe you? I still don't understand your role in any of this," I said, then mentally cursed myself for revealing that lack of knowledge. It was a rookie detective mistake.

"Oh for buck's sake. You've already seen what happens to you, Moon— Moondancer! I'm trying to save your life, you crazy mare! I don't expect you to understand why, but the fate of Equestria is at stake," she said. I noticed her eyes twitch upwards as she said the last bit, a telling indication of an intentional mistruth. She was very nervous about the message she was conveying, and it was seeping unconsciously into her mannerisms.

"Look, I'm not leaving for Ponyville. That's just stupid. If you really have Equestria's interests at heart..."

"I don't, okay! It's selfish," she yelled. "I admit it, what I want is selfish! But it's in your best interests, too. Just leave Canterlot for one day, that's all I ask. Please."

"And leave Twilight here defenseless against you?" I said. "As if."

Twilight's face contorted in frustration, and then her eyes brightened slightly. "Okay, you know what? Fine. Stay here. But you'd damn well better tell Twilight I was here. Tell her I'm waiting for her. Tell her everything we talked about, as soon as you see her. Are you at least smart enough to do that?"

"Well, obviously," I said, rolling my eyes.

"Okay. That... yes, that should be enough. Yes. Tell her I was here. I have to leave now to turn my... to see somepony important," she said, and turned and galloped for the door as her wings flashed back to visibility.

I watched her leave, stunned.

Who the buck was that, I thought? Was this really Starlight Glimmer I was dealing with? I couldn't think of anypony else who could possibly imitate Twilight to that degree, with the obvious yet notable exception of Princess Celestia.

Or could it have been Twilight herself?

If it actually were Twilight Sparkle, she'd lost too much weight in a few short hours—she had to be a copy from another universe. But why the hay would she pretend to be Starlight pretending to be herself? I couldn't believe that any Twilight would lie to me that way, at least not if the emotion spell had finally ended. Whoever it was, they definitely had emotions.

As unlikely as it seemed, a visit from Starlight Glimmer was still the leading theory. I felt like I was missing an obvious clue, though. There was something about the way she looked, but I couldn't quite put my hoof on it.

I came to my senses after a moment, and trotted to the door to see if I could catch which way she went. I was too late. Nopony was outside other than the guard. Day had just recently given way to Night, and Starlight could have cantered behind any number of buildings. I took a few steps out the door to gather my bearings and immediately tripped over some sort of thick branch or something, which was lying right there on the sidewalk. Without looking, I angrily kicked whatever it was into the bushes.

"Are you alright, Miss Moondancer?" asked the guard. He walked over to help me up.

"I'm fine," I said, and sighed as he lifted me up. "Just not liking this rolling cast at the moment. Did you see where Twilight went?" I asked.

"Towards the castle," said the guard, but this was unsurprising information as most of the city lay in that direction.

Feeling defeated after my embarrassing tumble, I went back inside to wait for the 'real' Twilight. I felt lost without her. I didn't have to wait long, however. She arrived within the hour. Unlike the previous intrusions, she knocked before entering.

I knew the moment I saw this Twilight that she was the real deal. She didn't have the stupid hair band on, and her face was totally expressionless. The emotion spell was still up.

"Hello, Moondancer. I have a testable theory," she said as she shut the door behind her with her magic. "Is there anything important to report before I begin?"

I looked into her eyes and felt my heart sink. Starlight really, really wanted me to tell Twilight that she had been here. It seemed clear she'd known what would happen in the future, and she was trying to muck with events that had occurred in the past, undoubtedly to change something. I just had no idea what, or why.

Then I wondered: should I tell Twilight Sparkle the truth about Starlight's visits? Or would that be playing directly into Starlight's hooves? After a brief moment of thought, I determined the answer was yes. I should definitely tell Twilight what had happened. Withholding information wouldn't help us to defeat Starlight. However, I couldn't tell her yet, not while she still had that accursed spell up. I had no idea whether or not Robo-Twi would react sanely to the news that Starlight Glimmer had been here, not to mention the fact that Starlight apparently had the ability to copy Twilight Sparkle almost perfectly.

"Moondancer?" asked Twilight. I realized I'd been staring off into space.

"Oh, sorry. Yeah, something happened, but it's not important," I said. "We can discuss it later, though if you could drop the emotion spell, it would help..."

She shook her head. "No. I'm leaving it up until we shut down the lab, for added safety."

I sighed. Having a spooky emotionless friend didn't feel safe to me, but she was probably right. "Okay then. I'd really like to hear your theory."

Twilight nodded and sat down with me on the couch. "Actually, first I should inform you that I've completed my death spell. I figured it might be useful in the future."

"I'm a little curious how it works," I said. "A lot curious, really."

"It translates the subject's past few days of experiences into a narrative form," she said. "The result of the translation would read just like a story from that pony's perspective, except everything would conspicuously be in the past tense, even the subject's sense of self, since there would be no 'am' or 'is' for the subject anymore."

"That's rather odd. It's too bad you weren't able to cast it on my corpse, although I'd hate to have to do it myself. I'd already know I was doomed before I got to the end of the 'story'," I said.

At that exact moment, I had a very strange feeling of deja vu. I ignored it, as I had never believed that mundane mental phenomena had magical causes. Theories about consciousness being magical were still held by some researchers, but they lacked solid evidence. I had always been a scientist, first and foremost.

"That said, here's the more important news: I'm fairly certain I've figured out time travel of the third form," she said. "I can predict what will come out of the rooms."

"Awesome! I'm all ears. Figuratively speaking, of course."

"Of course." Twilight pulled out a piece of parchment and a quill. "I was concerned about the potential for paradoxes and the overall inability to predict what comes out of the chamber, given that we now know it comes from some other universe we don't have a window into. But I've come up with a way that links the two worlds deterministically."

She drew a line on the parchment, and placed a dot in the middle. "Say this point on our worldline is where and when we initially open a test chamber. What comes out of the chamber," she said, drawing a second dot to the right of the first one, "needs to be predictable in our universe, even if another universe is involved. Otherwise, the two universes couldn't be causally linked in the first place."

"Agreed. I came to a similar conclusion earlier today," I said. "If it's not time travel of the first form, there has to be some hidden causal connection linking the two universes a priori."

"It turns out there is a link, and it's remarkably simple. I realized what it was when I started thinking about attempting paradox experiments," she said.

"Paradox experiments as in: you open the door, and if there's something inside, you choose to put nothing in the chamber the second time you open it; but if there's nothing inside, you choose to add something instead?" I said, and Twilight nodded in the affirmative.

"Exactly," said Twilight. "If we attempted that experiment, I predict there would be something in the chamber. Here's the logic. What ends up in the chamber is determined by tracing the worldline from the point the door is opened for the first time," she said, drawing a parallel line below the dot with its own two dots, "under the assumption that nothing appeared when you first opened the door, which is this parallel universe, below." She labeled the upper line "our universe" and the lower line "identical universe, except test room is empty".

Then she drew three arrows. One arrow traced from the upper-left dot (first experiment, our universe) down to the lower-left-dot (first experiment, universe where nothing was found in the chamber). The other two arrows traced from the lower-right dot (second experiment, the latter universe) up to the upper-right dot (second experiment, our universe), then backwards up to the upper-left dot.

Twilight waited as I took a minute to absorb the idea, and then I gasped in surprise. "Twi, that's brilliant! I can't believe I didn't think of it first!" I squealed. "The prediction function is just the expectation for what would have happened if there were no field at all, and all the quantum effects in the interim... I guess they get 'pre-rolled' to determine what comes out, sort of?"

She nodded. "Essentially, yes. In laypony's terms: what comes out of the first experiment is what we would have put into the second experiment, if nothing at all had come out."

"So the process connects us to a new, past-identical copy of our universe where that event did happen," I deduced. "I'm fairly certain those 'dice' get 'rerolled' again after the door opens, which could lead to inaccurate predictions if we were taking quantum measurements. But for most macroscopic experiments, quantum noise wouldn't have a realistic chance to affect the outcome."

"That was my thought as well. This means we should be able to deterministically predict what will come out of the antimatter chamber if we plan a particular paradox in advance, provided we can be certain we follow through with putting something into the second chamber to annihilate it, even if nothing comes out," said Twilight.

"Hmm. Well, we'd have to use a stooge who didn't understand the experiment, or a robot, or something like that," I said. "Otherwise we wouldn't want to put something into the chamber after nothing came out, which would mean nothing would come out in the first place."

"I've been thinking about that too. Back when I thought we were dealing with time travel of the first form, I was concerned that Starlight could have found a way to use a spell to make the antimatter invisible even when I was downstairs the entire time for that so-called 'six minute' experiment," said Twilight. "It might be possible to cast a spell directly into the magilectric transducers themselves, with a delay trigger. We would have missed the spell with our scans because the transducers are shielded. I don't think this is time travel of the first form, but if it's possible to use the transducers to hold spells it would give us an easy way to control the experiments automatically."

"I don't know if that's possible or not, but even if it isn't, it would be easy enough to use robots to do it," I said.

"I concur. I'm sure you realize what this means," said Twilight.

I did, and the implications were arbitrarily large. "I can hardly believe it, but the conclusions are unavoidable. We could duplicate anything, Twi! Free energy, free matter, all of it, right at our hooftips!" I was grinning from ear to ear, but I felt a chill when I saw Twilight's face remain inert.

"We'd have to hide the technology and maintain strict control over it, but yes. This is the greatest discovery in the history of ponykind," she said, flatly. Her lack of enthusiasm was seriously creepy.

"Wait a moment," I said. "This isn't timelines anymore, this is separate universes entirely we're talking about. That might explain why the device sucks up so much power in order to function. But how does it work logistically?"

"The universes are tied together based on that one difference," she said, pressing her hooftips together demonstrably. "Every branch from a freshly-opened chamber creates a separate universe where that chamber is empty, and that's the universe that determines what appears in the other one."

"But wouldn't we just be tapping into universes that already exist, using the multiple-worlds view of quantum mechanics?" I asked.

Twilight shook her head. "That isn't possible, because nothing about the experiment's framework allows us to connect to other possibilities. It has to be creating some sort of a loop. If this isn't time travel of the first form, then we're literally creating a separate branch of the universe every time we open a door."

I frowned. "Well, that's a problem. If we run paradox experiments to gather resources, we're always connecting one-way. The other universe would need to be otherwise identical to ours, right? So there would be a Twilight and Moondancer there doing the same thing, except it fails, which if your theory were true, would be neigh-impossible."

Twilight opened her mouth, then closed it for a few seconds before opening it again. "You're right. That is odd. Any paradox experiment would have to work asymmetrically, so it would necessarily create a statistically improbable universe. Everything in that universe would be exactly the same, except that an accumulation of bizarre quantum effects would somehow cause their instance of the experiment to fail."

"Well, crap. This sounds like a zero-sum game. I can't see how stealing resources from multiple identical universes is remotely ethical," I said.

"No, it can still work," said Twilight. "The math is weird because we're pairing up an infinite number of possibilities with each other. Even if there are two universes after we open a door, the odds of being in the winning universe aren't simply fifty percent. The odds are nearly certain."

"So... that means all the remaining experiments a 'losing' universe attempts would be neigh-certain to succeed, even though they're also creating two losing universes with each attempt they make," I realized. "Weird. That might actually work, but I'd need to check the math first."

Twilight nodded, then furrowed her brow. "No, wait. Each attempt should create only one universe. If we don't put anything into the doorway the second time it opens, then there's only one universe that gets created: the one we take stuff from."

"It doesn't work that way, Twi. We always have to open the door twice to complete an experiment," I explained. "If we put nothing in, then the air in the chamber goes back in time. Even if we could use a true vacuum, the absence of matter would go back in time. Each experiment must directly create two new universes: the one we take from, and the one we send to. Indirectly, there's no limit on how many spring into being each time we open a door—it could almost be infinite."

"Okay, here's a thought. Assume the air in the chamber goes back in time to a losing universe. Couldn't it go to the same losing universe we've borrowed from?" asked Twilight. "That would create a closed timelike loop between the two universes, and then we'd only be creating one universe with each experiment."

I shook my head. "That's impossible because the odds of the two universes are drastically different, as you just pointed out," I said. "Plus, we could always perform the experiment where we send something different back in return, which would necessarily break the loop. You can get a perfect closed timelike loop to work in a single universe with time travel of the first form, but in that case quantum effects can conspire such that the probability becomes certain on both ends of the loop. With time travel of the third form, you have to make two new connections each time, no exceptions."

"I'm not sure I like the implications of that theory. If we make two universes with each experiment, we'd be creating an exponentially-growing number of universes every time we use the machine," said Twilight. "That means the preponderance of bad universes might be able to catch up to the good ones, and the experiment would once again be unethical."

"There's nothing left to argue about. Let's do the math and see," I said, and Twilight nodded.

We readied our quills, each of us hoping Twilight was wrong.