Can we travel back and forth in time? The idea of time travel has been so infused into the human imagination from the time when “time” was seen as a physical entity, that there have been innumerable imaginaries working on the prospects of time travel. Remember “Back to the Future” series of movies that came up decades ago? It was not unique. There have been dozens upon dozens of examples of paradox, and they are all highly accurate in the way they portray time travel. They have covered the problems that could come up by changing time and its sequence, and they are all named paradoxes of time travel that we all have been intrigued with.
Physics has proven that time is only relative, and that time travel could indeed be possible, at least theoretically. But with this possibility, come a lot of speculative stances of the creative crowd of people, who have imagined situations that could not make sense in an event of time travel. Although this possibility has not been refuted by science, an issue of “causality” has come up. The question of who caused a series of events in the past. Time travel paradoxes are such paradoxes, that are logical contradictions associated with the possibility of time travel. These paradoxes have been studied in enough detail to put them into two groups: consistency paradoxes and causal loops. Some famous paradoxes are grandfather paradox, predestination paradox, and the like.
Predestination Paradox
The predestination paradox, or causal loop, is one of the most used ideas in almost all time-travel based fictional works. In simple terms, this paradox claims that sequential events in time are bound to take place again and again, even though a person might try to go back in time to change the course of events. Movies like “Predestination” have shown that by going back in time to change an event, all that the actor does is make sure that the event actually takes place, instead of avoiding the event altogether. Backwards travel in time would lead to incidents, and histories that came out of nowhere, and this “self-existing” possibility is a paradox in itself. Thus, if a person moves back in time in order to change the time itself, it would lead to a course of events that would, at some point in the future, send back the same man in time, to change the same thing. This is a never ending loop which could keep going on and on, and this idea has amazed people. This has led to a further qualified paradox, which is called Bootstrap Paradox, which will be discussed shortly.
Grandfather Paradox
This is a paradox which is different from the Predestination Paradox in a very elemental way: the time traveler removes his or her own possibility of existence, which leads to a paradox. Suppose, the time traveler goes back in time and kills his or her own grandfather before the grandfather actually met the grandmother. This way, it would ensure that the time traveler would never be born, and if the birth would never take place, no one would go back in time to kill the grandfather. In this case, the time traveler would be born ultimately, and go back in time, and so on. This is a seemingly bizarre paradox, which has been shown in decades-old movies, such as “Future Times Three” and stories like “Ancestral Voices” by Nathaniel Schachner. Broadly speaking, this paradox refers to a change in history that would remove the cause/means of traveling back in time altogether. That would ensure that there is no going back in time in such a parallel future, which means that the sequence of events would occur anyway. There have also been imaginations about “auto-infanticides” in this concern, where the time traveler goes back in time and kills his or her own self when they were a baby. There have been negations of this paradox, such as, ideas like the past is unchangeable, so the grandfather must have survived the killing attempt in past, and so on.
Bootstrap Paradox
This paradox comes from the idea of pulling oneself over a fence by one’s bootstrap, which is an impossible event of holding one’s bootstraps, and tugging up in an attempt to cross the fence. Imagine a situation, when someone actually went back in time and told Galileo that Earth was not the center of the universe. Now Galileo went on and discovered all the details, and came up with numerous works on his findings. The original time traveler who went back in time, in a future self, gets one of those works, and finds out about Galileo’s work. If the person goes back in time to enquire about “how did this idea come?”, what would be the answer? Did the idea come from the time traveler, who read Galileo’s work to know this? Or did it come from Galileo, whom the time traveler had told this? Who originated this idea? This event leads to a closed loop of information and incidents, where the origin of the events is not known, but they take place anyway. This timeline of close looped events is called bootstrap timeline.
Conclusion
Thus, as we can see, time travel, as a scientific possibility has never been ruled out. What has been contested is the question of cause-and-effect. If someone goes back in time and causes something, the effects do not seem to comply with the idea. There have been theories about time taking a wholly parallel path after such an incident of time travel, but that is speculation as well, and until someone actually goes back in time and does something, we will not be able to find out what could happen. We can only wait till it might take place.