By the new, based on real-life theories (no matter how bizarre it sounds) every trip back in time creates a new branch on the timeline tree.
Yes, exactly. I subscribe to the theory of timelines in this universe branching out from a common origin billions of years ago.
Say you start with one timeline and someone has to make a choice between two things. If realities branch out, then you have a timeline where this someone decides to do A and a timeline where they decide to do B. Two realities branching out from one origin point. Now let's say in both realities, this someone has two choices to make once again. Two timelines have now become four.
There are many possible futures but, if we look backwards, then the further back we go, the more in common these futures have with each other.
That's how, in science fiction, characters can travel into the future and then, ultimately, the future doesn't turn out to be that way.
It's also why the further into the future we try to predict, the more improbable it becomes. The slightest difference can affect everything else.