Marvel Studios
Would-be time travellers have long wrestled with the grandfather paradox: if you change things in the past and prevent yourself ever existing, how did you time travel in the first place? In other words, if Alice goes back in time and kills her grandfather Bob, she won’t have been born and can’t carry out her murderous plot.
One way to avoid such paradoxes is the idea of branching universes, in which the universe we are in splits with each instance of time travel, creating two different universes …
source: newscientist.com