In reality we live in the multiverse. Multiple timelines exist and if you were to travel back along a timeline and change the future as you knew it you would be creating a new and different timeline.
That timeline already exists. All possible timelines exist. The mind of God level stuff.
See here—> https://youtu.be/p4Gotl9vRGs
My brother’s friend Hugh Everett III said that but then he killed himself (Everett did — different manner of departure from published accounts).