Some ideas are:
- You branch off into another timeline and your actions make no difference to the previous timeline
- You’ve already taken said actions but just didn’t know about it so nothing changes
- Actions taken can have an effect (so you could suddenly erase yourself if you killed your parents)
- Only “nexus” or fixed events really matter, the timeline will sort itself out for minor changes
- something else entirely
I think the first one leaves open what you do, as alternate actions lead to an alternate timeline. The second is more “read-only”, similar to what OP laid out.
The only difference between the first option and the response is that the response posits that all possible timelines exist in advance and rather than generating a new timeline with your decisions, you simply navigate to the one that represents them. It’s a distinction without meaning, especially because the first option doesn’t strictly specify whether the timelines existed in advance or not. It simply says “you branch off into another timeline” with no requirement that it be one generated as a result of your actions.
The second option is called “closed loop” or Novikov self-consistency and specifically requires that the outcomes of your choices align with the past already as defined, simply in ways you did not know. It’s what they use in 12 Monkeys and the 3rd Harry Potter book, and it limits free choice, unlike the first option and what the above poster’s response stated.
I think what you’re doing is combining closed-loop and multiverse theories to say that the multiverse theory IS closed-loop simply because the multiverses existed in advance, whereas closed-loop is intrinsically single universe/timeline.
I appreciate those detailed insights, I see where I misunderstood. I need to reread the 3rd HP novel with my son now :)
It’s my favorite of the series, though I hate what JK Rowling turned into. Hope you and your son enjoy!