This is it, then, the moment of truth.
The weight of fifty years of studies carried in her head. The length of five lives lived and gone. For one moment of conviction and understanding.
Well, not completely. All these studies are very important and useful on their own, even without any consideration of your intention of demonstrating to Celestia that you are a time-traveler. Besides, if I were only intent on convincing her, I simply needed to bring along a long list of descriptions of new species found in places that haven't been explored yet... I did the studies because now I can learn whatever I want, without consequences.
She approached Celestia’s chamber, a hoof over her saddlebag, full of precious knowledge that she carried from the future, which was the past for her.
“My faithful student, what important matter is it that you wish to tell me about?”
“My dear teacher, I bring to you incontrovertible evidence that our understanding of time is wrong. Time travel is not only possible, it is repeatable, and I stand in front of you as an example of a pony who has lived through hundreds of time travels involuntarily.”
“Explain your concept of ‘time travel’.”
“I created a magical construction accidentally, and afterwards I found that, every time I die, I become transported back to an exact location in space-time, so that the moment after death, I find myself standing in the Canterlot library, at time several hours before the changeling invasion. This happens every time after death. My memories, personality, and other mental facilities are transported seamlessly, but my physical body is not transported at all.”
“Present your evidence.”
“You know very well that I should have lived through only twenty-seven years of age, and as such, despite my extraordinary talent, I could not have known all that there is to know in this wide world. Indeed, you also know very well the exact fields of studies I am familiar with, them being the five magics, history, and astronomy. However, with the help of time travel, I can study many years in one life, then die, and go back many years to start the process again. Thus, In my past five lives, I have been studying diligently, acquiring a vast knowledge that is impossible to acquire without time traveling. All this knowledge is examinable, and I will stand before any examining expert to validate myself.
Further, I have brought discoveries from the future: new potions, new spells, new species. I detailed them in my scrolls in my saddle bag. The new potions are all synthesizable using existing material and techniques. The spells are rather specialist, but should be understandable by any professor after reading it through a few times. The new species are recorded along with a drawing, a list of traits, and places to find them.
This is all that I wish to report, your highness.” Twilight groveled, awaiting Celestia’s understanding.
“Demonstrate your learning.”
“I can demonstrate here and now my learning in Old Alpine Language and Piano-playing.”
Princess Celestia nodded and asked a question in Old Alpine. Twilight replied, gave some commentary on the locative case of the noun, and then asked Celestia back, all in Old Alpine.
“Have I demonstrated to your satisfaction?”
“Will you play a piano song for me?”
“What song would you like?”
“‘Little Belle’.”
Twilight played at the piano in the room. She didn’t play perfectly, but her performance was remarkably good for a first attempt.
“I shall arrange these scrolls to be verified. Despite the wildness of your claims, the evidences you presented are very solid, and as such I will take your claims seriously.” Celestia nodded, “You may go now. I will tell you my judgment by the end of the week.”
Twilight waited until the end of the week, and heard back from Celestia.
My faithful student, Twilight Sparkle,
I have deemed your claims to be believable. Please come immediately so that we might discuss the matter further.
Your teacher,
Princess Celestia
Twilight’s heart fluttered in wild joy as she read the short letter. She galloped to the throne room where Celestia was waiting.
“My dear student, I...”
Twilight knelt down and started laughing and sobbing, “Sixty years of solitude...”
“Twilight, I -- ”
“Sixty years of loneliness, sixty years struggling inside this loop, nopony understood me, on the edge of madness and emptiness...”
Celestia came down from her high seat to embrace Twilight. “I am sorry that I didn’t believe you in your past lives.”
“Dying again and again, reborn again and again, nopony ever saw what it was like, nopony to confess to without fearing psychiatric confinement...” Twilight kept raving on and on, pouring out all the frustrations and loneliness, bottled up inside her for six decades.
“But we can fix this. We will find a way to break this cycle.”
Celestia appointed Twilight, now one of the most capable pony in both magic and physics, as the head of a research team on time magic. The research began by a thorough examination of the spell Twilight used to create the time loop, and proceeded to a detailed recreation of the exact method Twilight used when she attempted the spell.
This completed the first stage of the research. Very small scale experiments confirmed that the magical construction was capable of creating many kinds of strange distortions in time, the exact quantity and quality of the distortion depending sensitively on the details of the construction.
Twenty years of research later, the progress was discouraging. Only very few constructions could be reliable made, and even them were studied only on very small systems -- usually on cubes smaller than 1 millimeter in length, as scaling the experiments up always risked affecting the researcher ponies themselves.
It was a Friday night, after work. Twilight pranced around the empty lab agitatedly. She had planned a meeting with her friends, who had moved to Canterlot to keep close with her, but she did not feel like going for now.
What is needed is subjective studies. All these objective observations can only bring us so far. Unless we can make the cubes talk, we will never understand what effects these constructions have on these cubes. And the more important problem is that these cubes have no soul. They cannot tell us what effect the spells would have on souls... I'm the only soul that's subjected to such a spell.
I will have some patience, but I don’t want to wait so much longer. The research drags on and on without a goal and I miss my younger times. And even if it were to succeed? Even if the research actually does stop me from getting reset every time I die, what good would it do?
Suppose that it is possible for suicide to be rational – which is a reasonable enough assumption, in some unusual but not impossible circumstances – and suppose that at some future time, I can calculate that it is better for me to die forever than to continue existing – which is also a reasonable enough assumption, if we trust the many arguments against immortality – so I activate the loop-breaking spell, then suicide?
There is a problem here when expected life length is infinite. The proof for the rationality of suicide assumes that the domain of integration for the utility function is compact, which is not true when the domain extends to positive infinity. In fact, it’s easy to construct utility functions that are ∞-differentiable, bounded, uniformly continuous, integrable, have infinitely many dips below zero for increasingly long periods, and at any point, the tail of the integral diverges to +∞. Any simple-minded suicide-decision program, when fed with this function, will mistakenly decide to suicide after reading the function for some finite time, thus throwing away the +∞ utility.
Five more years was all that convinced Twilight that the research was going in a dead end. Small-scale experiments on nonliving things yielded no more data, and experiments on living non-talking things did not appear any more different than experiments on nonliving things. Large-scale experiments were strictly forbidden, not only for the safety of the world, but also for a selfish reason: Twilight was afraid that large-scale experiments might break her cycle, which she was not yet willing to do.
But still she stayed in this world, in order to conduct one more experiment: see if dying from an old-age induced heart-attack would result in a different reset.
“Well that didn’t work.”
Apparently, there’s no difference. Any kind of death results in the same reset. Should have appeared obvious in hindsight.