Board Thread:General Discussion/@comment-5413572-20170219072514/@comment-5413572-20170224023758

Would you care to provide the canon evidence that these timelines are in fact just in their heads? Because I can't recall that information being dropped anywhere in-game (outside of Flowey's post-Pacifist dialogue, but again, that's a questionable outlier). If there's canon confirmation that no alternate timelines are being created, then whatever, but as it stands, that idea doesn't really make much sense.

And like I said, regardless of how SAVING and LOADING actually work, Gaster attempting an experiment with those mechanisms and not having a SAVE point with which to anchor himself could still account for him shattering.