- Predestination paradox
A predestination paradox (also called causal loop, causality loop, and, less frequently, closed loop or closed time loop) is a paradox of time travel that is often used as a convention in science fiction. It exists when a time traveller is caught in a loop of events that "predestines" or "predates" them to travel back in time. Because of the possibility of influencing the past while time traveling, one way of explaining why history does not change is by saying that whatever has happened must happen. A time traveler attempting to alter the past in this model, intentionally or not, would only be fulfilling their role in creating history as we know it, not changing it. Or that the time-traveler's personal knowledge of history already includes their future travels to their own experience of the past.
In layman's terms, it means this: the time traveller is in the past, which means they were in the past before. Therefore, their presence is vital to the future, and they do something that causes the future to occur in the same way that their knowledge of the future has already happened. It is very closely related to the ontological paradox and usually occurs at the same time.
A dual example of a predestination paradox is depicted in the classic Ancient Greek play 'Oedipus':
Laius hears a prophecy that his son will kill him and marry his wife. Fearing the prophecy, Laius pierces newborn Oedipus' feet and leaves him out to die, but a herdsman finds him and takes him away from Thebes. Oedipus, not knowing he was adopted, leaves home in fear of the same prophecy that he would kill his father and marry his mother. Laius, meanwhile, ventures out to find a solution to the Sphinx's riddle. As prophesied, Oedipus crossed paths with a wealthy man leading to a fight in which Oedipus slays him. Unbeknownst to Oedipus the man is Laius. Oedipus then defeats the Sphinx by solving a mysterious riddle to become king. He marries the widow queen Jocasta not knowing she is his mother.
A man travels back in time. While trying to prevent a school fire he had read about in a historical account he had brought with him, he accidentally causes it.
An example of a predestination paradox in the television show Family Guy (Season 9, Episode 16):
Stewie and Brian travel back in time using Stewie's time machine. They are warped outside the space-time continuum, before the Big Bang. To return home, Stewie overloads the return pad and they are boosted back into the space-time continuum by an explosion. Stewie later studies the radiation footprints of the Big Bang and the explosion of his return pad. He discovers that they match, and he concludes that he is actually the creator of the universe. He explains his theory to Brian, who replies with "That doesn't make any sense; you were born into the universe. How could you create it?" Stewie explains that it is a temporal causality loop, which is an example of a predestination paradox.
A variation on the predestination paradoxes which involves information, rather than objects, traveling through time is similar to the self-fulfilling prophecy:
A man receives information about his own future, telling him that he will die from a heart attack. He resolves to get fit so as to avoid that fate, but in doing so overexerts himself, causing him to suffer the heart attack that kills him.
Here is a peculiar example from Barry Dainton's Time and Space:
Many years from now, a transgalactic civilization has discovered time travel. A deep-thinking temporal engineer wonders what would happen if a time machine were sent back to the singularity from which the big bang emerged. His calculations yield an interesting result: the singularity would be destabilized, producing an explosion resembling the big bang. Needless to say, a time machine was quickly sent on its way.
In all five examples, causality is turned on its head, as the flanking events are both causes and effects of each other, and this is where the paradox lies. In the third example, the paradox lies in the temporal causality loop. So, if Stewie had never traveled back in time, the universe would not exist. Since it would not have existed, it could not have created Stewie, so Stewie would not have existed.
One example of a predestination paradox that is not simultaneously an ontological paradox is:
In 1850, Bob's horse was spooked by something, and almost took Bob over a cliff, had it not been for a strange man stopping the horse. This strange man was later honored by having a statue of him erected. Two hundred years later, Bob goes back in time to sight-see, and sees someone's horse about to go over a cliff. He rushes to his aid and saves his life.
In The Big Loop the Big Bang owes its causation to the temporal engineers. Interestingly enough, it seems the engineers could have chosen not to send the time machine back (after all, they knew what the result would be), thereby failing to cause the Big Bang. But the Big Bang failing to happen is obviously impossible because the universe does exist, so perhaps in the situation where the engineers decide not to send a time machine to the Big Bang's singularity, some other cause will turn out to have been responsible.
In another example, on the show Mucha Lucha a teacher goes back in time to stop a flash from blinding him in an important wrestling match, when the three main protagonists try to stop him due to dangerous possible outcomes he unleashes a disco ball move thereby blinding himself in the past causing the future he knows to that day.
Another example is in "The Legend of Zelda: Ocarina of Time", when the player travels to the future and meets a man in a windmill, who tells him about a mean Ocarina kid who played a song that did something to his windmill. He then teaches Link the song, who plays it in the past, causing him to learn the song in the future.
In most examples of the predestination paradox, the person travels back in time and ends up fulfilling their role in an event that has already occurred. In a self-fulfilling prophecy, the person is fulfilling their role in an event that has yet to occur, and it is usually information that travels in time (for example, in the form of a prophecy) rather than a person. In either situation, the attempts to avert the course of past or future history both fail.
Examples from fiction
Many fictional works have dealt with various circumstances that can logically arise from time travel, usually dealing with paradoxes. The predestination paradox is a common literary device in such fiction.
- In Robert Heinlein's "—All You Zombies—", a young man (later revealed to be intersex) is taken back in time and tricked into impregnating his younger, female self (before he underwent a sex change); he thus turns out to be the offspring of that union, with the paradoxical result that he is his own mother and father. As the story unfolds, all the major characters are revealed to be the same person, at different stages of her/his life. In another of his stories, "By His Bootstraps", the protagonist in a series of twists, interacts with future versions of himself.
- "The Man Who Folded Himself" is a 1973 science fiction novel by David Gerrold that deals with time travel and the predestination paradox, much like Heinlein's. The protagonist, Daniel Eakins, inherits a time belt from his "uncle" that allows him to travel in time. This results in a series of time paradoxes, which are only resolved by the existence of multiple universes and multiple histories. Eakins, who repeatedly encounters alternate versions of himself, finds himself in progressively more bizarre situations. The character spends much of his own contorted lifetime at an extended party with dozens of versions of himself at different ages, before understanding the true nature of the gathering, and his true identity. Much of the book deals with the psychological, physical, and personal challenges that manifest when time travel is possible for a single individual at the touch of a button. Eakins repeatedly meets himself; has sex with himself; and ultimately cohabitates with an opposite-sex version of himself. Eventually, that relationship ends up with a male child who he finally realizes is him, and he is now his own "uncle".
- In the SpongeBob SquarePants episode SB-129m, Squidward, inspired by 'jellyfishing', teaches prehistoric SpongeBob and Patrick to catch a jelly in a net. This means that Squidward invented Jellyfishing.
- In the video game Timesplitters: Future Perfect the main protagonist, Sergeant Cortez, often helps himself solve puzzles, and protects himself during hard situations.
- In Flatterland, Vikki Line and the Space Hopper fall into a black hole, are rescued by future versions of themselves, and then go back in time to rescue themselves.
- In the film 12 Monkeys, James Cole travels into the past to stop an attack attributed to the elusive "Army of the Twelve Monkeys", which leads indirectly to the formation of the group. The fatal shooting at the end of the movie is witnessed by his childhood version and leads to the nightmares that haunt him throughout his life.
- In The Twilight Zone 2002-2003 revival, there is an episode in which a character (played by Katherine Heigl) goes back in time to assassinate Adolf Hitler while he is a baby. She kills the baby (whom she presumes to be actual Adolf Hitler, though the viewer might note it seems like a very normal baby, perhaps not very dark hair), but the nanny (discovering the death) replaces the baby with a street gypsy's baby (the mother being a very crazy looking woman who has black hair resembling the Hitler we know), and she presents this baby to the father as his own. The father proceeds to introduce this son to his guests as "Adolf", presumably the Adolf Hitler known to history in the first place.
- In Bill and Ted's Bogus Journey the antagonist, unhappy with the future, sends evil robots back in time to kill Bill and Ted. When his robots are defeated, he goes back himself and takes control of the world's satellites so the whole world can see them defeated. Instead, the whole world watches them play their music, cementing their place in history. In Bill and Ted's Excellent Adventure we see that the band could not have formed if not for Rufus appearing from the future to help them with their history project.
- The episode "Roswell That Ends Well" of the animated television series Futurama puts a more humorous spin on the paradox. In the episode, the main characters go back in time to 1947 in Roswell, New Mexico, sparking the Roswell UFO Incident. Meanwhile, Fry, told that the death of his grandfather Enos would nullify his own existence, becomes obsessed with protecting the man. He shuts Enos in a deserted house in the desert in order to protect him, failing to realize that the house is in a nuclear testing site. The resulting atomic test kills Enos, but Fry does not disappear. Fry later comforts Enos' fiancée, no longer believing her to be his future grandmother. He has sex with her, only to realize afterward that she is his grandmother and therefore he is his own grandfather.
- The video game Prince of Persia: Warrior Within, the Prince is chased by the Dahaka, whose purpose is to preserve the timeline by erasing the Prince from it. Unable to fight the monster, the Prince travels to the Island of Time to kill the Empress of Time, who created the time-manipulating sands from the first game. He hopes to prevent the sands from being created, since it was the sands that put him in his current predicament. However, the Prince realizes too late that killing the Empress is what creates the sands, and hence he becomes the architect of his own fate. A secondary paradox is the Sand Wraith, who seems to stalk the Prince throughout the first half of the game, even trying to kill him at one point. The wraith is killed by the Dahaka shortly before the Prince kills the Empress. After killing the Empress, the Prince realizes that he can change his fate by using the Mask of the Wraith, which transforms him into the Sand Wraith and sends him back in time a short distance. He learns that the wraith (who he now understands to be his future self) was trying to protect him, rather than attack him. Upon reaching the point at which the Dahaka is supposed to kill him, the Prince uses his knowledge of the encounter to have his younger self die instead, ending the mask's power and creating a grandfather paradox as well.
- The film Donnie Darko incorporates an example of fictional predestination paradox. Donnie avoids death by a jet engine that appears out of nowhere, only to later, because of information he has learned since, send the engine back in time himself so that he may die by it. He thereby negates all activity that occurred between the appearance of the engine and him sending it back, including his learning of the reason that he must die. This is explained through use of a tangent universe and a physical and temporal theory.
- In Harry Potter and The Prisoner of Azkaban, Harry is saved from the Dementors by a stag patronus. At that time, he thought it was his dead father's spirit of some sort watching over him. After traveling back in time, he realizes he was the one who produced the patronus- after watching himself being attacked and seeing that no one had produced the stag patronus- he himself casts the spell, producing the stag patronus he had seen earlier. Similarly, in the film, Harry and his friends are alerted to the presence of the Minister for Magic when a rock hits Harry in the head; but after traveling back in time, Hermione recognizes the same rock and throws it at Harry herself.
- In the Legacy of Kain video game series, more specifically Soul Reaver, Soul Reaver 2, and Defiance, the predestination is evident in the Soul Reaver as well as Raziel, whose soul is contained inside. Through the storyline of the 3 games it is learned that Raziel's soul must become part of the Reaver, despite the fact that it has been a part of the weapon the whole time. Defiance ends in Raziel being stabbed by the Reaver, allowing his soul to be transferred to it, however because of the purification his soul had gone through earlier the cycle is broken rather than beginning again.
- In the Terminator films, Skynet, a computer program that controls nearly the whole world in the future, sends a machine to the past in order to kill John Connor, the future leader of the human resistance, at different points of his life: once before he is conceived (by killing his mother, Sarah Connor), again when he is 10 years old (in Terminator 2: Judgment Day) and a final time a few days before Judgment Day happens (Terminator 3: Rise of the Machines). In the second film Dr. Dyson (Joe Morton), the lead scientist for the Skynet project, explains that the surviving arm and CPU chip of the original Terminator was analyzed and found that the technology was so advanced, they (humans) would have never invented the technology themselves and was used to create Skynet in the first place. However, all the components and research were destroyed in an attempt to prevent Skynet, but in (Terminator 3: Rise of the Machines) Skynet is built anyway without any information or components from the future, implying that it was inevitable. In a not yet made movie, the humans somehow successfully invaded the complex in which the time machine is placed, manage to send someone else to the past so that the Connors can be protected, which is what starts the series. In The Terminator, the machines send the T-800 and the humans send Kyle Reese: Kyle will be John Connor's father (that is, if Skynet had not have happened, Kyle Reese would have no reason to go back in time to protect Sarah, and thus John Connor would not have been born).
- In the episode "He's Our You" of the television series Lost, several characters travel back into the 1970s. One of them, Sayid Jarrah, encounters the younger version of Benjamin Linus, the leader of the Others, and a man who has committed various acts such as betraying the Dharma Initiative and causing their complete genocide by the Others, the manipulation and deceit towards various people on the show and caused much strife to Sayid personally including recruiting him to become an assassin during his wife's funeral. When Sayid meets Ben's younger version he believes that it is his destiny to kill him and prevent all of the bad things he does from ever happening. However when he does this by shooting him, Ben is taken to the Others where they state that they could heal him in a mysterious temple but, "his innocence would be lost" and he would "always be one of them." By trying to prevent Ben from doing the things he did, Sayid actually caused him to become the evil manipulator that he is and caused all of the evil acts he committed.
- In Artemis Fowl: The Time Paradox, Artemis's mother contracts the deadly magical disease, Spelltropy. To save his mother, he travels into the past to save the Silky Sifaka lemur, which he kills at age 10 by handing to the Extinctionists. In the past, Artemis the elder meets Opal Koboi, who follows Artemis into the future. In the present, Opal gives Artemis's mother Spelltropy-like symptoms, which causes Artemis to time-travel in the first place.
- In the 2008 episode of Doctor Who: "The Doctor's Daughter", the TARDIS takes the Doctor, Donna, and Martha to find the source of the Doctor's Daughter's signal. However, the TARDIS arrives early, which leads the Doctor to the accidental creation of his daughter, thus activating the signal. In the 2010 episode "The Big Bang", the Doctor is released from the Pandorica by Rory Williams, using the sonic screwdriver supplied by the Doctor after his release.
- In Red vs Blue, when the character Church is thrown back in time in Episode 50, he tries to prevent certain things from happening, in the process leading to everything becoming the way it was: kicking dirt on a switch hoping it to be replaced, instead it was kept and later got stuck; giving his captain painkillers to prevent a heart attack, but killing him because the captain is allergic to aspirin; trying to make the tank not kill him by disabling the friendly-fire protocol, which later proves his death; telling the tank and robot that they should not leave and build a robot army, thereby giving them the idea to do it; trying to shoot O'Malley with the rocket launcher only to shoot Tucker because of the launcher's highly defective targeting system and his inability to aim.
- In the PlayStation 2 video game Shadow Hearts: Covenant Karin Koenig, one of the main protagonists, falls in love with Yuri Hyuga. She is gently rejected because Yuri still has feelings for the exorcist Alice Elliot, who died in the previous game. Unrequited love does not stop her from fighting alongside Yuri, though, until at the end of the game when she is flung into the past and meets Yuri's father. There you finally see a picture she is given earlier in the game by Yuri's aunt that shows his father, mother and Yuri as a child. It's obvious the woman in the picture is Karin, thus making her Yuri's mother. She ends up being the only one staying in the past because she knows she is to become Yuri's mother and assumes the alias "Anne". She also takes back a cross Yuri gave to her, which is the same cross that belongs to his mother. The cross becomes an Ontological paradox.
- The Black Sabbath song "Iron Man" tells the story of a man who time travels into the future of the world, and sees the apocalypse. In the process of returning to the present, he is turned into steel by a magnetic field. He is rendered mute, unable verbally to warn people of his time of the impending destruction. His attempts to communicate are ignored and mocked. This causes Iron Man to become angry, and have his revenge on mankind, causing the destruction seen in his vision.
- In The Penguins of Madagascar, the episode "It's About Time" sees Kowalski constructing a time machine called the "Chronotron". A future Kowalski tells Private to convince his present self not to complete it. After he decides to destroy the Chronotron, another Kowalski from the future tells Skipper to convince him to save the Chronotron. When the present Kowalski spots his future selves, a vortex appears. The present Kowalski activates the Chronotron and goes back in time to talk to Private. When Private points out that if Kowalski had not invented the Chronotron then he would not have gone back in the first place to tell himself not to make it, the future Kowalski then goes back in time to talk to Skipper. Rico then throws the Chronotron into the vortex, sealing it. While a baffled Kowalski tries rationalizing that such a simple thing defies all laws of the universe, Skipper simply states that Rico is a maverick who makes his own rules, and tells Kowalski to invent something that will not destroy the world.
- In the Red Dwarf episode "Timeslides", Dave Lister travels back in time using a mutated photograph of a pub in Liverpool where his band once played a gig to give his teenage self the idea of inventing the Tension Sheet (a stress relief tool invented by Fred 'Thickie' Holden, a former classmate of Arnold Rimmer, which earned him millions). This causes him to become rich and famous in the past and never get stuck on Red Dwarf. Arnold Rimmer, in an attempt to experience fame and fortune for himself, travels back even further in time to his school days, to give his own younger self the idea of inventing the Tension Sheet instead. Unfortunately for Rimmer, while he is giving young Rimmer the idea, the conversation is overheard by Thickie Holden (who sleeps in the next bed) and he is able to patent the idea before young Rimmer can, therefore putting everything back to how it was at the start of the episode.
- In the PC game Fallout 2, there is a side quest where the protagonist enters a time travel device and travels back in time to Vault 13, prior to the events of Fallout 1. During this time travel period, the hero sabotages the vault's water chip, thus starting the series of events of the first game and ultimately the birth of our hero. After sabotaging the water chip the game informs us that the hero "feels better about his future".
- In The Transformers episode "The Key to Vector Sigma", Optimus Prime assists in the creation of the Aerialbots who, in the later episode "War Dawn", are sent back in time and become instrumental in the creation of Optimus Prime, thus ensuring their own creation in the future.
- In Sam & Max Season Two there exist 2 examples of this paradox:
- In "Ice Station Santa", Sam and Max must save their future selves from being killed. In "What's New, Beelzebub?" they are saved by their past selves; this creates a never ending cycle of "save and later be saved; the savers are later saved".
- In "Chariots of the Dogs", Sam and Max are given an egg by their future selves from "What's New, Beelzebub?" who they also give a remote control too. Later, in What's new Beelzebub S&M give their past selves the egg and get the remote from them which, once again, creates a never ending cycle. However it is still unknown how the egg got into the hands of the Future S&M's in the first place.
Prior to the use of time travel as a plot device, the self-fulfilling prophecy variant was more common.
In Revenge of the Sith, Anakin Skywalker has visions of his wife dying in childbirth. In his attempt to gain enough power to save her, he falls to the dark side of the force and becomes Darth Vader. His wife is heartbroken upon learning this and argues with him. In his anger, he uses his power to hurt her, which eventually leads her to die in childbirth.
Shakespeare's Macbeth is a classic example of this. The three Witches give Macbeth a prophecy that he will eventually become king, but the offspring of his best friend will rule after him. Macbeth kills his king and his friend Banquo. In addition to these prophecies, other prophecies foretelling his downfall are given, such as that he will not be attacked until a forest moves to his castle, and that no man ever born of a woman can kill him. In the end, fate is what drives the House of Macbeth mad and ultimately kills them, as Macbeth is killed by a man who was never 'born' as the man was torn from his mother's womb by caesarean section.
In the movie Minority Report, murders are prevented through the efforts of three psychic mutants who can see crimes before they are committed. When police chief John Anderton is implicated in a murder-to-be, he sets out on a crusade to figure out why he would kill a man he has yet to meet. Many of the signposts on his journey to meet fate were predicted exactly as they occur, and his search leads him inexorably to the scene of the crime, where he cannot stop himself from killing the other man. In the end, the prediction itself is what had set the chain of events in motion.
In Lost, Desmond Hume's future flashes regarding Charlie's deaths eventually lead to his death. Desmond has a vision in which Charlie pushes a button below a flashing light which allows the other castaways to be rescued just before he drowns. However when the event occurs, events happen slightly differently than in Desmond's vision and it is suggested that Charlie may have been able to save himself without jeopardizing the hopes of rescue, if he had not believed his death was crucial in the rescue of the other castaways.
Yet there are examples of prophecies that happen slowly, if at all. In Red Dwarf: "Stasis Leak", when Lister travels back in time to meet with Kochanski to marry her, he finds out from his future self from 5 years later that he is going to pass through a wormhole and end up in a parallel universe version of Earth in 1985 but after 8 whole series, this has never happened (although similar events happen in "Backwards").
In the Harry Potter Universe by J. K. Rowling a prophecy by Sybill Trelawneyis overheard by Severus Snape about the birth of a wizard "with the power to vanquish" Voldemort. This prophecy was only partially overheard by Severus Snape, who relayed what he heard to Voldemort. To stop the prophecy from coming true, Voldemort attempted to kill Harry while he was an infant, but his curse backfired on him, separating his soul from his body for 13 years, and transferring some of his powers, as well as a part of his severed soul, to Harry. Dumbledore tells Harry several times that the prophecy is only true because the Dark Lord believes it. Harry is free to turn his back on it, but the fact that Voldemort will never turn his back on it, and therefore never rest until he has killed Harry, makes it inevitable that Harry will have to kill Voldemort, or vice versa.
- Grandfather paradox
- Newcomb's paradox
- Ontological paradox
- Self-fulfilling prophecy
- Temporal paradox
- The chicken or the egg
- Time loop
- Time travel in fiction
Time travel General terms and concepts Temporal paradoxes Parallel timelines Philosophy of space and time Spacetimes in general relativity which
can contain closed timelike curves
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