Nearly every Sci-Fi movie about time travel deals with the causal loop paradox. However, not all movies deal with time travel the same way. Sci-Fi movies involving time travel often deal with, and struggle to solve, the concept of a temporal paradox or causal time loop. The paradox is often ignored in movies like Back to the Future and Terminator, while Triangle and Predestination cleverly make use of it as a twist in the last act.
The causal loop paradox can be described as a self-fulfilling prophecy. This paradox occurs in a time travel story, where the events that will happen in the future are dependent on the past. If the future is affected by the past, how does the loop begin? Because there is no way to start the time loop, it becomes both inexorable and absurd. This problem is constantly being faced in Sci-Fi movies, regardless of whether it’s due to technology or superpowers. Take a look at the best time travel movies for examples.
The Terminator is James Cameron’s most memorable movie. However, it is also an excellent example of a causal loop and all its problems. Kyle Reese is sent back to the future by Skynet to save Sarah Connor. He also has to stop a cyborg assassin from returning from the future. Sarah must be saved in order to give birth to John Connor, the future leader and resistance member. As Sarah and Kyle fall in love, it becomes clear that John is the father of John. The paradox is that John Connor exists only because he sent his father back in time. How did John Connor become a man in the original timeline before Kyle Reese traveled back in time? The Terminator cannot resolve the problem.
Back to the Future is also a tricky movie. Marty and Doc travel back in time to the 1950s and Marty meets the teenage version of his parents, Lorraine, and George. Marty alters a timeline to save George in a car accident. Marty must then get his parents together so he can exist when Doc and he return to the future. The unanswered question in both movies is where it all began. This mystery remains unanswered partly because the movie’s focus is elsewhere, namely on FX-driven action and adventure, but also because attempting to answer it would only make the movies more confusing.
Certain movies are more direct when it comes down to the causal loop paradox. The clever Sci-Fi movie Triangle reveals that the killer who is following a yacht upside down is actually a future version. The killer is trapped in a loop of hunter-hunted. Ethan Hawke, a transgender detective, is sent back in time to prevent a bombing in Predestination. Only to find that he is also the bomber and investigator. Hawke’s supervisor wanted to expand his authority beyond the limitations of time and placed him in a time loop.
The causal loop paradox can be solved in two ways. One, you can use it to add a twist to the plot or the other is to ignore it completely to keep the spectacle from being lost. The paradox is interesting and leads to intriguing questions for high-brow genres like Predestination or Triangle. The entertainment value of blockbuster movies such as Back to the Future and Terminator is not diminished by the absence of a real explanation for the causal loop. The Sci-Fi movies leave the inner-workings of the time loop largely unresolved in all cases.