Board Thread:General Discussion/@comment-10452902-20170507091901/@comment-10452902-20170514073629

He literally says in his battle dialogue timelines suddenly stopping and new ones starting. So no, it is possible, at least in the Undertale universe. You are looking at this from a real world view, that is wrong I mean it's the wrong way to look at things when we are talking about a fictional world where magic exists. In Undertale, you do change the timeline. Your very first attempt at a pacifist playthrough results in a neutral ending where Frisk disappears and monsters are still trapped behind the barrier. BUT when we reset, we do things a bit differently and create the true pacifist timeline. We may not know what happens after Frisk's disappearance in the neutral timeline but as we passed through the barrier, it is safe to say that the timeline can continue without us however, if we truly erase that timeline when we reset which is what the game tells us, then that timeline no longer exists. So once we create the true pacifist run, that timeline no longer exists as the main timeline if at all. Don't forget that there are many ways to get the neutral endings and by that I mean kill only certain people or a certain individual or only kill the common enemies instead of the boss monsters, all create unique timelines. Thus, you are creating new timelines, you are sort of changing the past.

In short, the game tells us one thing and you are trying to contradict it and look at things from a real world perspective and that is why you are wrong.