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.

The predestination paradox is controversial because it seemingly negates the "common sense" notion that we are responsible for our own destinies, and, with adequate knowledge and preparation, we can alter their courses. The predestination paradox says the exact opposite, leaving doubt in believers' minds if they really are independent, or just puppets on strings.

Examples

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 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 typical example of a predestination paradox (used in The Twilight Zone episode "No Time Like the Past") is as follows:

A man travels back in time to discover the cause of a famous fire. While in the building where the fire started, he accidentally knocks over a kerosene lantern and causes a fire, the same fire that would inspire him, years later, to travel back in time.

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.

A final example is:

A man is hunting when someone shoots him. Surviving, he resolves to go back in time to stop the sniper. Appearing at the place of the incident, he sees someone approaching, and shoots the man, believing the man is the sniper. Later, he realises that the man he shot was a past version of himself, and so he was both the sniper and the victim.

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 second example, the person would not have traveled back in time but for the fire that he or she caused by traveling back in time. Similarly, in the third example, the man would not have overexerted himself but for the future information he receives.

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 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

Main article: Predestination paradoxes in fiction

Time travel

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 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), but the nanny (discovering the death) replaces the baby with a street gypsy's baby, 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 the Spongebob Squarepants episode "SB-129", Squidward inadvertently creates the sport of jellyfishing while in the past, which is the reason he ended up in the freezer, for if the sport had not been invented, the chain of events would have not happened. This is another example of a causal loop.

• In television, 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 are thrown back in time to Roswell, New Mexico, in 1947, sparking the Roswell UFO Incident. Meanwhile, Philip J. Fry, told that the death of his grandfather Enos would nullify his own existence, becomes obsessed with protecting the man. To this end, he shuts Enos in a deserted house in the middle of the desert in order to protect him, failing to realize that the house is in fact on 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 (thanks to the Professor) that she was/will be his grandmother after all because Fry has just made her pregnant, making him his own grandfather. Meanwhile it is also revealed that the UFO that landed in Roswell was actually Bender the robot, and the alien they found was Dr. Zoidberg. This is the same theme in the 1982 film Timerider: The Adventure of Lyle Swann, where the main character goes back in time to the Wild West and has sex with a beautiful cowgirl. He later learns that he is his own great-great grandfather, and that woman is his great-great grandmother.

• The video game Prince of Persia: Warrior Within, the second in the Prince of Persia trilogy, centers heavily around predestination paradoxes. In the game, the Prince is being chased by the Dahaka, a being 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 in order to kill the Empress of Time, who created the time-manipulating sands from the first game. In doing so, he hopes to prevent the sands from being created, since it was the existence of 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 (his father's Animagus form is a stag). 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. Note that, had this rock not been thrown by her in the first place, she wouldn't have recognized it later on, and wouldn't have known to throw it. Also, after throwing the rock, Hermione hears a strange snapping sound coming from behind her. When they travel back in time, Hermione accidentally steps on a twig and breaks it when trying to inspect her hair from the back.

• 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.

File:Terminator 2 Endoskeleton Arm.jpg

Dr. Miles Bennett Dyson examines the right arm of the first Terminator in Terminator 2: Judgment Day.

• 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 13 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 movie 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. In the final movie, the humans, who have successfully invaded the complex in which the time machine is placed and have finally defeated the machines, always 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: the first will give the people in the past the necessary components that will end up starting the Skynet project, and Kyle will be John Connor's father (that is, if the time travel hadn't happened then Skynet wouldn't have been created and John Connor wouldn't have been born). In (Terminator 3: Rise of the Machines) the TX terminator injects nano-probes into the primitive T1 -suggesting that her advanced technology is partly responsible for the terminators of the future. It is interesting to note that it does not occur to any of the main characters that the war cannot be stopped for one obvious reason: there are Terminators in their time period. The chronological series of events are: Terminator components found in 1984 leads to Skynet; Skynet starts the war; after the war Skynet begins to exterminate the human race; the resistance forms; Skynet knows the war is lost and develops time-travel; various Terminators are sent back in time to kill Sarah, John etc. The existence of Terminators in our time means the war happened in the future.

• 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 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 antibiotics 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.

• In the video game Fallout the player character is cast out of their home to find a replacement water chip. In the sequel in a random event called The Guardian of Forever the player character enters the vault shortly before the events of Fallout 1 and breaks the water chip.

• 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 doesn't 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 eariler 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, but it is not known whether she is aware of this or not when she is given the photo.

Prophecies

Prior to the use of time travel as a plot device, the self-fulfilling prophecy variant was more common.

Shakespeare's Macbeth is a classic example of this. The three Weird Sisters 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 cesarian section.

In the Philip K. Dick short story "The 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).

See also

• Recursion
• Newcomb's paradox
• Ontological paradox
• Time travel in fiction
• Grandfather paradox
• Self-fulfilling prophecy
• Causality
• Time
• Time loop
• The chicken or the egg