Time travel implications with various philosophies Talking about time travel as a realistic scientific possibility seems... far fetched to me. But I do love conversations about different models of time travel in fiction.
For me, in fiction, there are 3 basic models of time travel:
1. One univerese, you can't change the past, just re-enact it. This is like 12 monkeys. When you go into the past, you can certainly do stuff and feel like you're making choice, BUT those choices are already necessarily part of that past - your actions during your time travels are a necessary part of the past and were already a part of your history, you just didn't know it.
2. One universe, you CAN change the past. This is probably what most people imagine when they talk about time travel. Pretty sure Back to the Future was like this. When you go back to the future, the future you go back to is different from the future you came from, because the past is different now.
3. Parallel timelines. When you go back to the past, you're not going into your OWN past, you're jumping into a parallel universe that's the same as your universe, but in the past. You can make choices in this universe that are different from the past of your own universe, BUT your own universe is still chugging along into the future without being affected by these changes. There are actually some REALLY interesting things you can say with this type of time travel. The Avengers End Game movie kind of had a model of time travel like this.
Those are the basic models, in my view. Some movies are kinda inconsistent with which model they choose. Some movies sort of mix-and-match. The recent film The Flash actually has an interesting model, that's sort of a combination of 3 and 1, with intersecting timelines which turn into spaghetti when you mess with the past.