Twilight stood still. Something had happened, and she could swear it was magical in nature. Worse, she didn't know what it had been. Even after all her studies, she was amazed how magic always found a way to surprise her. As with any kind of unknown magic, caution was primordial. At least she remembered that much as her short-term memories were in a blur. For now she kept her eyes shut, trying to remember what just happened. Her mind was fuzzy, as if someone just rebooted her brain, images slowly coming back of the previous moments.
There, a memory flashed back; she was in front of a series of books. Against her will, that automatically brought a smile to her face. She was looking for one... No, not one; she was looking at all of them, at their order on the shelf. Yes, that's it! She was pondering about her methodology to order the different books in Ponyville's library. She tried once a month to find a better way to classify them. So she was in the library... Her library, or she used to be, as she still had no idea of her current whereabouts.
She tested her body, trying her legs one by one. Whatever that peculiar magic had been, she could swear it affected her whole body and she needed to verify that everything was still in place. She was happy to find out that she didn't fall down with whatever happened and she was still standing up. Head, check. Neck, check. Tail, check. Wings... Concerns surfaced in her mind as she found out her wings were not answering to the call from her nervous system. In fear she quickly probed her horn to find out if it was still there. She let out a breath of relief. She had only gained those wings two months ago and she never really cared that much for them, but losing her horn was something else. She had really hated it when Discord stole that from her. It made her feel... naked. Powerless, even!
Of course, losing her wings could mean a lot of different things, from losing her alicorn standing; to sickness; or worse, some magic gone wrong. Considering she still didn't know how she really got them in the first place, regaining them could prove problematic. She knew the theoretical part about creating new and powerful magic, but if everypony who designed a new spell was awarded wings, there would be no simple unicorns left. No, there were other elements at play in the creation of an alicorn, and while she knew that friendship had something to do with it, she still didn't know exactly how.
She slowly opened her eyes, only to find she was facing the exact same bookshelf as in her memory. It would have been a source of reassurance if it wasn't for her brain automatically noticing that the order of the books was different. Worse, she couldn't find any of the books that were supposed to be in this section. Instead of geopolitical treatises, different tomes about mathematics and physics and their relationship with magic stood in front of her eyes. To make the matter worse, some of those books were not even supposed to be in her library! She spotted a tome about advanced teleportation of complex matter that was, as far as she remembered, under lock and key in Canterlot's library.
She closed her eyes again eyes and took a few deep breaths while trying to keep herself from hyperventilating. Somepony had come into her library and messed with it. At that very moment, she couldn't say what was worse; losing her wings or the disorder of the books.
"Hello, Twilight," a voice said behind her. Without mistake, that was a voice of an old pony. While Twilight couldn't say whose voice that was, her gut assured her it was a friend. She was unable to say how that was possible as she didn't know many old ponies. Granny Smith was a friend, and she certainly sounded old, but the only other aged friends she could think of were the Princesses. They were ancient, actually, but they didn't sound old at all.
She turned around and looked at the pony who had just spoken. It was an old earth pony mare who appeared to be well within her eighties, if not beyond. It was hard for Twilight to estimate earth ponies’ ages as they tended to have a longer lifespan. Even after years of trying, she never managed to find out Granny Smith's age, only that she was beyond a century old. Twilight stared at the pony, trying to guess who it was, but the sky-blue mare with a gray mane and turquoise eyes didn't ring any bells.
Noticing the confusion in Twilight's eyes, the older pony smiled and moved around to show her flank. A small, eight-pointed white star was still easily noticeable on the whitening fur. If there is something that never changed in a pony, it was a cutie mark, and Twilight could never forget that specific one.
It took a few moments for Twilight to gain control over her gaping mouth. "Azure?" Something sounded wrong to her ears, but for now the age of her friend was monopolizing her brain. While it should have been working overtime trying to solve that puzzle, for some reason it had decided to shut down and think about nothing. Twilight just stood there, staring at the old mare.
"It's been awhile," Azure replied while sitting down.
"I don't understand," Twilight said, staring at the other pony. Again, her voice sounded wrong, as if another pony had spoken.
Azure took a deep breath. "Simply put, I pulled your soul to the future and fixed it temporarily to another pony's body. As with any time travel spell, the fabric of space-time is now pulling backwards on what was done. In a few minutes you will be back to your own time and body." She ended up her explanation with a smile.
It took a few moments for those words to register properly in Twilight's brain, and even more for it to recover from the revelation and start processing that new information. After all, it wasn’t exactly her brain. When the light finally came on, she looked down to find two light green hooves. Working overtime to keep her breathing in check, she turned her head back and found a short blond tail. Her cutie mark was also different; a quill drawing a dark-gray pentagram. Her eyes went wide when she finally understood; it wasn't a mare's body!
"You're in my son's body," Azure explained. "Again, it's only temporary, and we don't have much time. He decided it would be better if you were to speak to me instead of him."
Twilight closed her eyes and put a hoof over her heart. She took a few deep breaths while moving her hoof away from and back to her chest. It took far longer than she expected for her heartbeat to slow down to an acceptable level. "I... I'll be alright. I think," she finally managed to say in her now disturbingly masculine voice. She deeply hoped Azure was right and it was only a temporary situation.
"I’m sorry. I didn't have any other choice. The quantity of magic needed to transport an object through time is dependent of three factors; the temporal distance, the spatial distance and..."
"The mass of the subject," Twilight concluded, as her brain switched focus from her predicament to the complex magic formula behind it.
Azure smiled. "Yes. In this case, eighty two years was too much to transport any significant amount of mass," she explained. Twilight frowned as she realized her estimate of her friend's age was off by over a decade. "At least with the quantity of magic me or my son are able to summon."
"A soul doesn't have any mass obviously, and by doing it in my library you reduced the relative spatial distance to a minimum," Twilight finished almost automatically for her. Azure nodded in agreement. Her mind focused now on some complex magic, Twilight barely noticed her panic had dissipated and her breathing was back to normal. "But why pull me into the future instead of traveling back in time?" The only time travel spell Twilight knew of, the one Pinkie Pie found in Canterlot's archives, was only designed to travel backwards. While that specific spell wasn't that hard to execute, she understood enough to know that reverse-engineering and rewriting it differently could very well take decades of work, if not longer. While a spell could be easy to cast, the formula behind it, supporting it, could be of orders of magnitude more complex and vice versa.
"Because I could not accomplish what I had in mind that way. Time travel is tricky and it took me a lot of time and effort to find out why," she explained while looking at Twilight, suddenly quite serious. "You cannot change history by going back in time. From the point of view of the traveler, events will always take place the way they already did… would have… will have… the way the traveler remembers them." Seeing Twilight didn't understand what she meant, she continued. "If for some reason you really plan to change things... Let's say you want to travel to a moment to meet yourself, but you don't remember seeing any future version of yourself at that moment, the spell will fail to send you there. Or worse, it will work, but send you somewhere else and you will still not meet yourself. Or events will simply unfold in a way that you don't meet yourself. In other words, you cannot alter events that already happened to you; they are fixed in stone. Pulling you forwards means you will still be able to change things. From the traveler's point of view, the future is yet to happen. What you are experiencing right now is only one possibility of your future, but it is the only past that can lead to my present."
Twilight let it all sink in for a while. "Wow." She didn't understand everything Azure had just said, but she guessed her friend had taken a lot of time to think about it.
"Yeah, don't think about it too much. It gives me headache, but it’s the only way we can even hope change events," she said softly. "Took me decades to find the errors in Constellation's original time travel spell, and even longer to design one that would allow me to reach my goal."
Twilight shook her head. "I doubt you brought me here to talk to me about time traveling, am I right?"
Azure nodded again. "You are. No matter how much I would love to chit chat, there's more pressing matters." She stood up and walked to a nearby window, which was covered by a curtain. With her mouth, she pulled it away.
Twilight walked up to the window and looked out. Where she expected to see Ponyville and a bright blue sky, there stood only ruins of buildings covered in ashes. The sky wasn't blue; it was a sickly brownish color. She looked up instinctively towards Canterlot hanging on the mountainside, but it wasn't there. All that was left of Equestria's capital was a few pylons of stone that had once supported the city's foundations.
Twilight recoiled at the sight, shaking her head. "No... no... What happened?" she finally managed to ask, unable to tear her eyes away from the ruins.
Azure was looking at the ground, almost in shame. "A little bit over week from the moment I pulled you... You, Luna, Celestia and Cadance will die. Poisoned." She looked up directly in Twilight's eyes. "And it's all your fault."