Predestination paradox
From Wikipedia, the free encyclopedia
A predestination paradox, also called either a causal loop, or a causality loop and (less frequently) either a 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" him or her to travel back in time. This paradox is in some ways the opposite of the grandfather paradox, the famous example of the traveller killing his own grandfather before his parent is born, thereby precluding his own travel to the past by canceling his own existence.
Because of the possibility of influencing the past while time travelling, one way of explaining why history does not change is by saying that whatever has happened was meant to happen. A time traveller attempting to alter the past in this model, intentionally or not, would only be fulfilling his role in creating history as we know it, not changing it.
In physics, the Novikov self-consistency principle proposes that contradictory causal loops cannot form, but that consistent ones can. In a physical sense, a self-consistent causal loop of this kind is not actually a paradox because it produces a logically consistent result rather than a contradictory one. It is only perceived as a paradox because it goes against conventional expectations and assumptions about causality.
[edit] Examples
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 paradox 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.
In both 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 first 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 second example, the man would not have overexerted himself but for the future information he receives.
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.
[edit] 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.
Prior to the use of time travel as a plot device, the self-fulfilling prophecy variant was more common, with two of the earliest and most famous examples being the ancient Greek legend of Oedipus, and the ancient Indian story of Krishna in the epic Mahabharata.
In the legend of Oedipus, it is prophesied that the baby Oedipus will one day kill his father and marry his mother. His father, Laius, attempts to circumvent the prophecy by abandoning the baby in the wilderness, where he was found by another King and Queen and raised as their son. Years later, Oedipus — unaware that he was adopted — learns of the prophecy and leaves home to avoid it. He kills a man and marries the widow, but does not learn until later that they are, in fact, his biological parents. The attempts to avoid fate result in the fulfillment of the prophecy.
In the story of Krishna in the epic Mahabharata, king Kamsa, afraid of a prophecy that predicted his death at the hands of his sister Devaki's son, had her cast into prison where he planned to kill all of her children at birth. After killing her first six children, Krishna was born. As his life was in danger he was smuggled out to be raised by his foster parents Yasoda and Nanda in the Gokul village. As a young man, Krishna returned to his kingdom to overthrow his uncle, and Kamsa was eventually killed by his nephew Krishna. It was due to Kamsa's attempts to prevent the prophecy that led to it coming true.
This is also seen in the episode of Futurama entitled “Roswell That Ends Well.” After going back to Roswell in 1947, Fry becomes obsessed with protecting the man who would later become his grandfather, Enos. To this end, he shuts Enos in a deserted house in the middle of nowhere, thinking that he was safe and so would be able to have children and then grandchildren. However, the house is blown up by an atomic blast. Fry comforts Enos' fiancée, no longer believing her to be his future grandmother as Enos died and Fry is still alive, and later has sex with her - only to later realize, thanks to the Professor, that she was his future grandmother after all, and Fry had just made her pregnant with Fry's own father, making him his own grandfather. There is also a Simpsons time travel episode, 'Time and Punishment' (episode 109, 1994) which parodies Ray Bradbury's 'A Sound of Thunder', another classic in the time travel genre.
In Star Trek:First Contact The borg attempt to stop the first warp flight of 21st century humans. The 24th century humans come to stop the borg, and in doing so convince the reluctant Zephram Cochrane to proceed with his warp flight. If not for the borg traveling back through time Cochrane would not have proceeded with the flight, thus causing a predestination paradox
In Star Wars Episode III: Revenge of the Sith, Anakin has vision nightmares that his wife will die in childbirth. In an attempt to prevent this, he turns to the Dark Side to gain the power to save her. But by turning to the Dark Side, he becomes corrupted and assaults her. This change in him causes her to "lose the will to live," and she dies shortly after childbirth. In attempting to save her, he caused the very death he was trying to prevent.
J. K. Rowling's book, Harry Potter and the Prisoner of Azkaban, also deals with causal loop paradoxes via a time traveling device called the Time-Turner. Rowling avoids making this obvious by making sure the early characters don't see any of the events changed, but rather hear things that could apply to either outcome. For example, Harry hears the "swish and thud of an axe", and assumes Buckbeak the hippogriff has been killed, but later discovers someone had swung the axe into the fence in frustration. In the movie based on the book, more direct paradoxes were added. When Harry, Ron and Hermione are about to be caught in Hagrid's hut, someone throws stones that break a container of flour and hit Harry on the back of the head, causing him to see the approach of Prof. Dumbledore with the Cornelius Fudge and the executioner for Buckbeak. Later, we see it is Hermione, who had travelled back to save Buckbeak with Harry, who threw the stones when she realized they "weren't leaving."
In the video game Final Fantasy VIII, after defeating the final boss, Sorceress Ultimecia, the main hero Squall Leonhart travels back in time and witnesses Ultimecia passing her powers on to Edea, thirteen years in Squall's past, he then informs Edea of the concepts of Garden and SeeD that she will create and Squall will become the leader of.
In the Terminator series, John Connor sends Kyle Reese back in time with a message. Kyle recites this message to Sarah Connor, who later teaches it to John. Furthermore, Kyle is John's father, and thus if Kyle had not been sent back in time, John would not have been born.
In the Planet of the Apes film series, after the planet is blown up by an atomic bomb in the future, two apes escape to our time, and their intelligent offspring are oppressed, causing an uprising that would set the course for the beginning of the planet of the apes in the first place.
In the episode of Mucha Lucha "Woulda Coulda Hasbeena", Senor Hasbeena remembers that a bizarre flash of light ruined his entire luchador career. Using a time first to travel into the past, Rikochet, Buena Girl, and the Flea attempt to stop him from ruining the future, forcing him to sue his signature move, the Funky DiscoBall. But when he uses the move, he causes the bizarre flash of light that ruined his career.
In the 3D animated television show Beast Wars (which is related to the Original G1 Transformers story line) the descendants of the original Transformers, Maximals (Autobots) & Predacons (Descepticons), travel back in time to prehistoric Earth, when their ancestors were still in stasis in the Ark. They almost cause the destruction of the Autobot leader Optimus Prime & therefore jeopardized their own existence - a classic Grandfather paradox. Even though they manage to save their ancestor & eventually return home to their own time, their actions in the past still altered their own future. It’s later revealed that their actions in the past were fortold by a powerful Oracle, therefore being a Predestination paradox.
