TheFoxsCloak

Originally Posted by TresserT

Someone explained this very thoroughly a couple of weeks ago.

In typemoon there are two views of the universe. The Actual Universe and the Observable Universe.

The AU is like a giant stone tablet with everything that ever has or will happen etched into it. There's no past or future, everything just is and is layed out clearly all at once. Likewise, events don't "unfold"- every "possibility" is actually just another etching. These etchings take the shape of branching lines, corresponding to the timelines as we understand them.

The OU is what humans actually witness. Imagine a blind person running their fingers along the lines in the etching in order to understand it. This is what gives motion to time. We start by feeling the past, and then running our finger down the line towards the future.

The problem is that the blind person, Alaya, only has limited energy. Running their finger across every single line on the AU is impossible. So when the line they're tracing starts repeating over and over (stagnation), they just give up on it and stop wasting energy tracing that line.

This is "pruning"- not really the destruction of a timeline, just Alaya no longer providing any energy towards it. That said, the observable universe is all humans are capable of observing. Worlds exist within the AU that are not traced by Alaya, but we can't even look at those worlds.

We do have the ability to simulate worlds like that ourselves (see: Lostbelts) but simulating an unobserved timeline and actually traveling to one are very very different.

The meta reason is probably just that this is a game and games where nothing happens are boring. But everything I said is the in universe narrative on pruning and the universe.