I stare at the whiteboard, my mind working on overdrive as I try to finish the theory. It's taken me days to write this theory; hopefully I'm right. A marker hovers in my aura while I read seemingly endless lines of mathematical equations, stretching on down the whiteboard both across and downwards. I make one more mark on the whiteboard, noting a potential solution.
With that, I turn my attention to the piece of parchment next to me, on which I have documented my findings thus far. Picking up a quill, I add to my writings my latest find.
"If closed timeline curves do, in fact, exist, then it would theoretically allow travel backwards in time, thus elevating the spectre of the grandfather paradox. However, the Neighnikov principle of self-consistency forbids this; if one tries to change the past, events will align to ensure the future remains the same."
I muse on this for a short while, wondering if I am correct. I have one doubt, that of the self-consistency principle. So, I set down the quill and proceed over to my expansive bookshelf, tiredly climbing up the ladder to locate a book. Row after row of book yields no results; perhaps I left it on my desk. I climb down the ladder, trotting over to the nondescript mahogany desk to see that of course, the book is gone. The bed, maybe? I drag myself to my bedroom, opening the door in my magic. Everything is exactly how I left it when I last was in this room two days ago. The bed is neatly made, the curtains closed. The wood floor is clear of any debris, the shelves still organised. I begin my search by checking the bed, then methodically making a pattern through the room. When I am finished, no crack or crevice is left that has not been searched.
Drat! Using my magic, I remove every book from the shelf, each one entering a swirling circle above my head. One by one I bring them down, scan the title, and replace them on the shelf. The process continues for awhile; book, scan, shelf. I soon find myself growing rather tired, but I press on nonetheless.
After hours upon hours of incessant searching, I tiredly stumble back to the whiteboard. I check my parchment, draft up an explanation in my head, and decide that it's time to tell my mentor about my theory, even though I haven't found the book quite yet. I can do just fine without it; I only needed it to cross-check my discovery. I check my study one last time before grabbing my saddlebags and proceeding to Celestia's quarters.
"Come in," Celestia says from behind the closed door. I oblige her by entering her spacious quarters, closing the door behind me. Exhausted, I glance up at her, no words coming to mind. She is standing over her desk, scribbling away with a quill. She glances over at me, seeing me in my tired state.
"Twilight?" she asks, dropping her quill. "Are you alright?"
I stumble around a bit, eventually coming up with an answer. "Mhmm. I've done it."
"Done what? You look exhausted," the princess adds with an air of concern.
"I've solved closed time-like curves," I say proudly. Of course, given that my theory is correct."
She gives me a confused look. "Really?"
"I thought you may l-like to hear my t-theory," I continue with a yawn.
"Alright." She leads me over to a chair, motioning for me to sit. I do, finding the chair incredibly comfortable. She sits down across from me, ears perked up, ready to hear my theory.
"So, in short, a closed time-like curve is a world line in a Lorentzian manifold of a particle i-in spacetime that is closed; which means returning to its starting point. The possibility-"
She smiles at me. "I know what a closed time-like curve is, my student. I don't want to rush you, but I think it would be best if you could get to your theory."
"R-right. Uh, anyway, if these do exist, it would first require a solution to general relativity to permit their existence. We can create this by arranging a series of light cones set up as to loop back onto themselves; thus allowing an object to loop in the spacetime system, returning to exactly the same place and time it started. This is only one possibility; the object's light cones in the future would display a possibility of motion in spacetime points both forwards and backwards in time, thus allowing for time travel." I pause to yawn. "My apologies. Anyways, if the object in question was a pony, then they would be able to go back in time in one of these closed curves and possibly change the past; the grandfather paradox, for example. Using this system, the spectre of said paradox is raised exponentially; however, the Neighnikov principle of self-consistency forbids this. If one tries to change the past, events will align to ensure the future stays the same. However, my theory is that while time travel is possible with magic, the system still must be able to account for self-consistency. This I know, because I have tried to change the past, to tell my past self to not disaster-proof Ponyville and... you know what happened. There is self-consistency in action."
Celestia remains silent for a short while, pondering my new theory. "Fascinating. How long did it take you to come up with this?"
"Three days," I say with a yawn. My mind hurts. I feel drowsy. Despite this, I know I have accomplished my goal; through the exhaustion, there is pride.
"Twilight, do you mean to tell me that you have been awake three days straight?" asks the princess, her voice concerned.
I nod in reply. I'm too worn out to say anything more.
"Oh, Twilight..." She lifts me up in her aura, carrying me over to the bed. My eyelids are heavy, the bed is cool to the touch, sleep seems so tempting. But I can't sleep. There is still work to be done.
"Twilight, hear me out. I think you need to rest now. Three days is too long." She pulls the blanket up over me, tucking in the sides.
"But..." I begin to protest. "There's still... still... to be..."
"Shhh..." She strokes my mane with her hoof. "Don't bother. You can continue when you're all rested up. I want you to stay here so that I can watch over you. I don't want you working yourself to the bone, my student."
"Okay," I say reluctantly. "Goodnight, Celestia."
"Goodnight, my student."
When I wake up, I find to my surprise that Celestia is there next to me, her wing wrapped around me protectively. She's holding me tightly in her forehooves, as if something would take me away from her at any moment. Drowsily I begin to sit up, seeing in my blurry vision that it is still dark. She stirs, I feel her shift next to me.
"Wha- what time is... Theory!" I stutter before a hoof caresses my cheek. Gently but firmly I am pulled down towards the mattress once more, the taller alicorn stroking my mane.
"Shhh..." she coos as she pulls me in close. "Rest, my student."
"Wait!" I protest. "What is the meaning of this?"
"You're so adorable..." She smiles at me as she strokes me, evoking a blush. "Twilight, it's two in the morning. You need to rest."
I sigh, closing my eyes. I am rather exhausted. Perhaps she is correct. Maybe I just need sleep. The rain pattering the windows and distant thunder soothe my mind, finally permitting me to rest on my own terms. As I doze off again, I hear her whisper in my ear. "I love you, my Twilight..."