The Rules of Time Travel: Fixed Loops, Branching Worlds, and the Cost of Change
Time travel may be the most deceptively simple idea in science fiction: go back, change something, come home. The simplicity lasts only until a story must decide what “change” means. Does the traveller complete a history that was already fixed, overwrite the world they left, create another branch, or visit a future that may never become real? Those possibilities are not interchangeable technical details. Each protects one kind of coherence by sacrificing something else. A closed loop preserves a single history but denies escape from it. A mutable timeline preserves intervention but makes whole lives vulnerable to erasure. Branching worlds avoid contradiction by allowing alternatives to coexist, while weakening the claim that anyone has truly repaired the past they came from. Once an institution can edit time, causality becomes political: someone must decide which disasters, inventions and futures are permitted to exist. Time-travel stories therefore disagree because they are not so...