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
The reason time depends on speed is because you are always moving at the speed of light, but the vast majority of that is going in the 4th dimension: time. If you speed up in a given direction you’re losing speed through time to make up for it.
I always found that idea so cool for some reason