Molly W commented on French colleague in China presents his opinion on time travel, particularly as it regards our hero Harper

Yeah, I agree with him. Timeline should be solved if time travel exists. Or, there will be multiple versions of the Time Traveler. Maybe both old and young version of Time Traveler exist in the same timeline. It will turn up contradictory; then it breaks the rule of physics. Time Traveler will also be stuck, or one of two versions will die soon.