Our imagination is the one place where causality is allowed to be violated.

Future is uncertain.

For any event, "what will happen next" has multiple potential outcomes, and in some cases, they are mutually exclusive. Thus, there could be a situation that has two potential outcomes (Event A or Event B), with a 50% probability of either occurring. There is just one event that will occur, and you can only experience this one event. Think of it as coming to a fork in a Y-shaped path. You can choose to go left or right, and once you make that decision, the other path disappears. An event could unfold in multiple different ways, but only one of those ways becomes true.

Three- to four-year-old children know future events are uncertain.

In a behavioral experiment (Redshaw & Suddendorf, 2016), children were presented with a Y-shaped tube, with the branches facing downward. A ball was placed into the top of the tube and children were instructed to make sure the ball did not escape. In theory, once the experimenter let go of the ball, it would travel down the straight portion of the tube and could then travel into either branch with equal likelihood. If children understood that the likelihood of the ball traveling into a given branch was 50/50, they should cover each exit with one hand to prevent escape. The findings indicated this was indeed the strategy that the children used, suggesting that they could prepare for an unpredictable future occurrence.

 

How does modern science fiction deal with the time paradox created when visiting the past?

"Back to the Future" is a cinematic masterpiece that cuts across cultures and generations. In the first movie, Marty McFly went back in time and inadvertently prevented his parents from getting together. This one event leads to multiple questions. Who gave birth to Marty if the history had been changed and his parents had never married? If he did not exist from the beginning, who stopped his parents' marriage? In order to avoid being erased from existence, Marty struggled to  let his parents eventually got together. This is a perfect example of why we cannot visit the past: because it goes against causality.

Time Patrol Bon is one of my favorite manga. In the future, where scientific technology has developed such that time travel is feasible, the time patrols go back to the past and rescued somebody who died unfortunately. One day, a boy named Bon was appointed as a time patrol and he devoted his whole life to using his newfound ability to saving people. Though some parts of this manga are futuristic fiction, actual history is also portrayed.

The creator of this manga came up with a great idea for the storyline. I was really impressed by his creativity. His idea was that a device could be invented that tests whether changing a particular person’s fate would drastically change history (some slight changes are acceptable, as this is necessary). Time patrols used this device and then were able to know immediately if history remained the same despite the change. This device avoids the time paradox and is essential to their mission. Because time patrols are not permitted to change history drastically, they sometimes need to turn a blind eye to the death of person whose fate might affect the course of history. This is a dilemma the characters struggle with occasionally.

One of the most interesting aspects of this manga is that it features many imaginary devices, which opens the viewer’s mind to all the possibilities that could occur if these devices existed in reality. One device stimulates the brain’s cortex to facilitate the flow of knowledge, and another device allows someone the ability to stay under water for a long time (longer than traditional scuba gear). It is a bit contradictory that despite such highly developed science, the patrols must physically visit the past to save someone. With all these fancy devices, isn’t there an easier way? In order to enjoy science fiction, we must suspend our disbelief and ignore everything we think we know about the world. We must be open to imagination. 

By allowing us to use our imagination, science fiction fulfills our dream to visit the past. This is one reason why science fiction attracts many people's interests. Early in development, we are primed to think about the uncertainty of the future. It is part of our nature.

Reference
Redshaw, J., & Suddendorf, T. (2016). Children’s and apes’ preparatory responses to two mutually exclusive possibilities. Current Biology, 26, 1758-1762.