It started with Einstein. If you can travel at speed of Light you will become an immortal. Your age is stopped at that time. This is not possibe to travel at speed of light. But in movies the script write start thinking about to travel across the time. In movies they can time travel to ancient time or very modern time. In other word they can travel to the past or to the future.
A question is here. Let's say A is the enemy of B and Bis unbeatable. There is no way to defeat B and B become a threat for mankind. So A decide to time travel and kill father of B or childhood of B. Will B vanish from current time? In some movies it happens and in some movies it is not.
I have watched one korea momve that extremely support first assumption. This is The Call (2020). In this movie past and present are interwined. If someone do changes in the past they will also affect the present time. Kim Seo-yeon visited to her mosther in 2019. Oh Young-sook, was living in the same house but in 1999. They can community through a phone line. Kim Seo-yeon finds the informations at that time and tell Oh Young-sook. But actually Oh Young-sook is murdered by her step mother not long after they communicate. But this time she did not die because Kim Seo-yeon helped her. This movie is too extreme in itme aspect because they changes occured in front of her own eyes. Oh Young-sook got upper hand because she is from past and she can make changes to Kim Seo-yeon's life. Another story I knew is Wolverine- Days of future past.
I also know some movies that did not support first assumption and follow second assumption. This is Harry Potter and the Prisoner of Azkaban(2004), At some time in the movie, Dementors attack Black and Harry, but an unseen figure casts a powerful Patronus. Harry thought it is his father first. But later he knew that it is not his father but rather himself. After he woke up he knew that Black has been captured and sentenced to death. So he and Hermione used her time-turner and back to the past. They go back to the time black was not capture and saved the black. He is watching his former self is circled by dementers so he casted Patronus. THen he understanded he saved himself. So this event is already happen. Present and past are merged and combine as one.
Another movie and Avenger's endgame. They have to go back to the past and gather the infinity stones. So the past will change but it did not affect the future instead it create Alternate Realities. After retriving stones they get back to the present time and after that. Banner wields the gauntlet and reverses Thanos's disintegrations. Finally Throns(from past) and his army vanished and half of the universe are resurrected.In this movies changes past did not alter future.
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