Finally, Twilight's preparations were complete. The magic circle was flawless, the time travel spell memorized, and she looked like she remembered herself: exactly her usual self. Well, usual except for the eye patch, she thought as she adjusted the black triangle over her right eye. This time, the spell wouldn't run out of power in the middle of the cross-temporal encounter. That much was certain. To be exact, everything that would soon have happened several days ago was certain. She began to cast.
*zzzap*
"Done! Next up, herbology in preparation for tomorrow's visit to Zecora's." Twilight was alone in the library, arranging all her time-travel related books back on the shelves. They were certainly very interesting, and shed a light on what exactly had happened when she tried time travel the first time. I was lucky I didn't cause a paradox, she mused. Time travel was definitely too dangerous to try without proper preparation.
Just as Twilight was about to float the last book into its space on the "Advanced Magical Theory" shelf, a bright flash erupted in front of her, and she lost her concentration. The book landed on its spine and flopped open, completely disregarded as Twilight blinked not only because of the bright light, but also in disbelief.
There was another Twilight, looking exactly like her, but wearing a stylish eye patch like the one from her earlier misadventure. "Hello, past me!" greeted the intruder. Her apparent enthusiasm struck Twilight as entirely inappropriate. "When are we?"
Twilight put her hoof to her forehead in anticipation of a headache. "Ugh, I can't believe I'll do the same mistake again. I must become out of my mind again. And for your information, it's Thursday."
Future Twilight frowned. "That's not a proper time coordinate, and we both know that. But since I remember saying that, I seem to have landed in the right time. Now, why am I here?" As she was speaking, Future Twilight took a seat on the most comfortable reading cushion in her room.
Twilight stared in indignant disbelief at her visitor. "What do you mean, why? Don't tell me I'll time travel without knowing why. Because I won’t. It's irresponsible. You're irresponsible!" She pointed a hoof at her future self.
Future Twilight rolled her eyes - well, at least the one that was visible. Rolling the one covered by the eye patch was inferred. "Of course you won't. I know perfectly well why I'm here. Now, why am I here?"
"This quiz doesn't make any sense. I can't know that."
Now it was Future Twilight's turn to facehoof. "Past me, this isn't a quiz. Seriously now: what do I always do when I don't know the answer to a question?"
Twilight didn't have to think long at that. "I'll research it. ...But how would I try to research why I'm here from the future? And why do you only speak in questions? And why am I wearing an eye patch again?"
This drew a genuine smile of pride from Future Twilight. "Very good! Those are the right questions... except for the eye patch. Now, what do you already know? What can you deduce from that?" Past Twilight found herself reminded of Celestia. The Princess would often teach her by asking questions, challenging Twilight to come up with answers herself.
"I know you're playing a game with me. I have to come up with answers myself, because you only ask questions. You only speak in questions because... huh. No idea yet." Twilight tried to switch tracks on the railroad of logic. "You're here because you want me to find out those answers. You're here now because... I'm alone?" She paced across the room, while Future Twilight regarded her from her seat on the cushion. "No, Spike was at Rarity's yesterday as well, while I was reading up on time travel. You could have come yesterday, except something important happened."
Future Twilight giggled. "Oh, this is great! I am - I mean, you are. I was, so smart! Go on," she urged, clapping her hooves excitedly.
Twilight raised an eyebrow at her eye patch-wearing double's praise. She thought about scolding herself for excessive pride, but she wasn't sure if that would be hypocritical or not.
The thought was filed away to be examined later, as she returned to her guessing game. "You came here today because it was important that I read about time travel first. That means that some crucial bit of information is in the books." She turned towards the bookshelf, noticing now the book that lay open on her floor. "Well, let's get to reading." As she approached the book, she saw it was opened to the heading "Chapter 5.2: Saddlestrap Paradox". She recalled reading it just last evening. It's about the paradox where knowledge is learned from nothing, when information from the future is necessary for that information to be sent back in time... The name comes from "pulling oneself up by one's saddlestraps".
For a moment Twilight didn't grasp the significance of the chapter, but then she burst into giggles. "Of course! I can't- I mean you can't bring information back from the future, so we decide to only ask questions." She glanced back at Future Twilight, who nodded approvingly, and continued. "I bet you knew that jumping to this point would open the book at the right page, too."
"Would you believe me if I told you it was a coincidence?" Future Twilight asked with a conspiratorial wink.
This didn't amuse Twilight. "Har har. Don't play with causality. So, we're trying to make a stable time loop free of paradoxes, while completing some other goal." Twilight plopped down on another cushion, facing herself. "Knowing me, this could simply be a test of stable time loops. If that's the case, I'm declaring it a success, and you can return now." The Future Twilight stared back. "Ok, now. Now? Nownownow?" Now it was Future Twilight's turn to look unimpressed. "No? Okay, so there's something else."
This gave Twilight pause. She was back to the original problem. How can I find information, that I'm not going to find without the help of Future Me? How can it not cause a paradox? Obviously the information had to be pre-existing. She tapped her hoof on her horn in thought. There are too many places to search. It could be in the head of any pony, at Canterlot Library, hidden undiscovered under a rock somewhere. There has to be a hint somewhere.
Twilight couldn't shake the feeling she was missing something obvious. Like she'd been close to the answer, but dismissed the line of thought with an answer that was too simple. My perspective is limited by the present... Oh, if I could get a hint from tomorrow's me... "Tomorrow's me... That's it!" She slammed her hoof onto her second-best reading cushion. "You didn't visit me tomorrow in the Everfree Forest, on my way to Zecora's hut. In the future, I would be alone in many different places, or you could approach me in disguise." She looked into her own eyes, seeking confirmation of her wild leap of intuition. "That means there is something in the library tree."
Now Twilight could feel a familiar soaring in her heart, the feeling of elation she got when she sensed she had every piece of the puzzle. All that remained was to fit them together. "I was going to have lunch downstairs, and raid the downstairs storage for herbology books, so I think need something in my room. I only keep three kinds of books here: my favorites," which I know inside and out, so that can't be it, "my to-read list," which I already have a reading schedule for, "and the trunk of donated books that I've been meaning to sort, eventually." Bingo.
Future Twilight was smiling widely in a mirror image of herself. Apparently, the final spurt of logic was as exciting to watch as it was to execute.
Twilight bounced up from her seat, almost tripping over her own hooves, and rushed to throw open the lid of the trunk. She plunged her head into the mass of books. "Already have that one... Trash novel... Read that at Canterlot... Coloring book... Trash novel sequel... Huh, so that's where my pink socks were... Aha, what's this? "Mare to Mare: 101 Tips for..." Twilight slowly trailed off and emerged from the trunk, holding a rather large book in her magical grip. With a confused look on her face, she opened the book on a random page. "Eep!" She immediately slammed it shut and blushed beet red.
Twilight turned to look at Future Twilight, whose body was now draped across her cushion in a languid pose. The time traveler’s eyebrow was raised in wordless question, and she slowly licked her lips. "Past Twilight, if there was a first rule of time travel sex, what would it be?"
"Don't become your own parent?"
"Fine, second rule."
Twilight tried to think of something that applied to this situation. It was hard, with a significant percentage of her blood still flowing to her facial capillaries instead of her brain. It's still her game. Her panicked heart was trying to beat its way out of her chest. There must have been hints. ...Saddlestrap Paradox. "You must not arrange for sex to be predestined. Past ponies must be able to give meaningful consent."
Future Twilight nodded. "If you say no, I'll go back to the future and you'll have to take this time trip to get rejected. If you say yes, well..." She winked her non-patched eye and licked her lips again for emphasis. "Of course, I already know what will happen, but it was still my decision when it was now in my past."
~~~
"Ah, ah, oh, past me! I didn't know it felt this good when I was you, sucking on my horn... I think I'm going to... ah! Watch out"
"Huh? Ow, my eye!"
"Phew... Oh, I'm sorry."
"What? Ow-ow! Why'd you do that?"
"Here, take my eye patch. You need it more than I do. It'll be sensitive for a few days. Hahh."
"Thanks. Oh wow, that was good. Except for the magic in my eye part."
"Yeah. Wow. I remember how good it was, and it's just as good for future you, you'll see. Which reminds me, I'll have to go back now. Oh horsefeathers-"
*zzzap*
Future Twilight emerged back into her own time as the time travel spell wore out. "-I gave her the eyepatch that I got from me."