"Do you remember that day, Twilight? When the Behemoth came to Canterlot?"
"Of course I do. Why is that relevant?"
"Do you remember the screams, Twilight? Do you remember the yelling, and the commotion, the creatures calling out? Do you remember all the confusion, Twilight?"
"Like it was yesterday. Why?"
"What did you hear when the Behemoth came to Canterlot, Twilight?"
"Silence, and its steps echoing through it."
"Did anyone speak, while the Behemoth walked through Canterlot?"
"No."
"And yet you remember the screams."
Imagine you have a deck of playing cards. All the cards are face down, you can't tell what type of cards they are, you can't move the deck, and you can't determine how many cards there are. The only thing you can do is draw. Now imagine that whenever you pull out a card from the top of the deck, the card turns into a different deck of cards. A normal one, and it can be for any possible type of game so long as cards are the primary focus. No two cards from the main deck ever produce the same deck, and the main deck seems to never run out of cards. Eventually, on a given draw, provided you keep drawing, the main deck will produce a new deck with exactly the same traits as the main one.
"That doesn't make sense."
And yet here we are. This is what this is. We know that's what happens, because we've seen it happen. There's a more interesting question though. One that is an actual question. Can cards from the new deck produce decks that are the same as the ones produced by cards in the previous deck? You see, that's the real crux of the matter. If the answer is no, then both decks are merely windows, and so will be every new copy of the deck made by a copy of the deck. But if the answer is no? What if an infinite number of perfectly identical repetitions is possible?
"Frankly, that seems like a pointless question. If they are identical in every aspect they may as well be one. What interests me is the variability of iterations. There are infinite numbers between one and two, but none of them are three. Is every kind of deck possible?"
That's not a question you can answer. Not in time, anyway.
"There are things in here that are best ignored. Books that are best unread, knowledge that is best unknown, memories that are best forgotten. And that is why I won't allow you to enter. But I can search for you, if you wish, if your wish is something I deem I can safely grant. Do not take it as an insult to your intelligence, Twilight Sparkle, the fact alone that you're here is enough to prove that you surpass many other creatures in that regard. And not to your wisdom either, you would not be allowed to remain if it were otherwise. But the fact remains that the words hiding in these halls could break and reforge any mind who happened to gaze on them. I trust you are wise and smart enough to know where your own limits lie."