Temporal paradox

For the controversy over the origin of birds, see temporal paradox (paleontology).

A temporal paradox (also called a time paradox and time travel paradox) is a paradoxical situation in which a time traveler causes, through actions in the past, the exclusion of the possibility of the time travel that allowed those actions to be taken.

The typical example is that of the grandfather paradox, wherein a time traveler goes back in time and kills his grandfather before his father is conceived. It is a paradox because if this occurs, he will never be born, and therefore never be able to travel back in time to kill his grandfather, thus allowing himself to be born.

Hypotheses

Currently, temporal paradoxes are the domain of science fiction and philosophy. Various schools of thought exist as to what would happen in the grandfather paradox were a time travel device ever invented.

Solution

The solution to this paradox is anything but simple. After the time machine is built it must be placed in a room with a man that must wait to use it. He must be sealed off from any outside distractions. The only way he will know when to use it is when he gets a message from a third party outside of the room (the note should have the exact time it was written and given to the man in the sealed room). He can only go back as far as when he was sealed in the room. After he is done with what he was sent back to do, he must give the same note to himself at exactly the same time as it was given to him. To solve the paradox however, the time machine would not work if the man isn’t going to give the note to himself. It would only work if the cycle could be complete. In this way, the machine has the ability to tell the future of the past. Even if the guy truly believes he would give the note to himself, the time machine wouldn’t work unless he actually will.

Time line protection hypothesis

The time line protection hypothesis posits that a time traveller would be incapable of causing a paradox, as the natural continuity of the timeline would cause any such interaction to fail. For example, he would appear in the wrong place (or fail to go anywhere at all), various twists of fate would conspire to impede him, or his actions would instead be responsible for the history he remembers.

A similar theory states that time travel may in fact be a factor in making the universe the way it is today; actions of time travelers are responsible for the present situation. Alternatively, any time traveller would take the utmost care in avoiding such paradoxes, inspired by the fear of the damage they could cause.

The animated television series Futurama shows a more lighthearted side of the paradox. In the episode "Roswell That Ends Well", the main character, Philip J. Fry, travels back in time with his friends to 1947 in Roswell, New Mexico. Remembering that his grandfather works at the base, and told that killing the man would nullify his own existence, Fry becomes obsessed with protecting him. Fry's efforts prove counterproductive: he locks the man in a shack to protect him, failing to realize that an atomic bomb is being tested on the grounds. When he doesn't disappear, he assumes that the man could not have been his grandfather and thus proceeds (unknowingly) to sleep with and (accidentally) impregnate his grandmother, thereby becoming his own grandfather.

1972 "Doctor Who" adventure Day of the Daleks. Sir Reginald Styles is targeted by 22nd Century guerrillas, who believe he's behind the deaths of VIP delegates. Because of those deaths, the Daleks were able to take over Earth in their time. In truth, a fellow guerrilla who was left behind was to blame, which was the true cause of their timeline ensuing.

In the game Ratchet and Clank Future: A Crack in Time, Alister Azimuth tries to fix his mistake of Causing the fall of the Lombaxes, but if he was successful in traveling to the past, time would rip itself apart and the universe would collapse on itself.

In the machinima series Red vs. Blue, Church is sent back in time via the combined energy of a bomb and a weather machine. He attempts to fix past events, as well as preventing the explosion, but his attempts are ultimately responsible for most of the events that took place beforehand in the series, including his own death.

In the Japanese manga Doraemon, the lead character's grandson came back in time to meet his grandfather in his primary school days intentionally to change the life he is in. The lead character questioned the existence of his grandson that if he did married the girl he likes (instead of the one he dislikes but conceived the father of his future grandson), what would happen to his grandson. His grandson along with Doraemon replied that there are multiple paths leading to the same future, and they will still exist even if the lead married another girl. The plot never explicitly told of when the history was altered, but later events in the plot did showed a future where the lead married the girl he likes and lived a better, wealthier life and yet, future characters showed no signs of remembering the original history. However, when being ask of the reason of Doraemon's reason of being in the past, he will reply his role is to make sure the lead marries the girl he likes, which mentally still reserves logic.

In the television series Lost, Jack and Locke enter an underground research facility on the island in 2004, and watch an orientation film made by the mysterious DHARMA Initiative organisation in 1980. The film makes reference to an "incident" having occurred on the island at some point in the 1970s, necessitating the construction of the underground bunker, as a method of containing a limitless amount of electromagnetic energy, and preventing a global catastrophe. In the show's fifth season, some of the main characters begin moving erratically through time, before eventually becoming stuck in 1974. Three years later, these same characters unwittingly become the cause of the incident.

Timeline corruption hypothesis

Another idea is that any change in the timeline, even without personal interaction, while allowable, would cause a "butterfly effect" in the timeline. All history after the time the traveler visited would be affected by minute changes the traveler had made in the past, and the history, depending on how severe the time traveller's actions were, would sooner or later be completely changed. This has been coined the "timeline corruption hypothesis." The 2004 film The Butterfly Effect and the Multiverser RPG system prefer this view. There's also the Ray Bradbury science fiction short story "A Sound of Thunder", in which the butterfly effect is caused by a real butterfly.

The most well-known example of this theory is the 1985 film Back to the Future, in which the protagonist Marty McFly goes back in time and interferes with his parents' first romantic encounter, thus erasing his own existence (as well as that of his family). However, the effect only happens gradually, exemplified by a family photo in his possession: each of his siblings begins to disappear limb by limb, starting with the oldest and working down to him (Marty is the youngest of the three). This allows Marty to correct the error and restore the timeline, albeit with a few minor changes that are due to his interference.

This idea also appears in a Family Guy episode, in which Peter goes back in time with the help of "Death" so that he can relive his teen life. When he arrives in the past, rather than spending the time with his present-day wife, Lois, Peter ignores her. His actions cause a corruption in the timeline, and when Peter returns to the present day, all of reality is radically different.

The timeline corruption hypothesis is also used in the Red Dwarf episode, Tikka to Ride, when the Red Dwarf crew travels back in time (with Lister's intention of ordering 500 curries) and accidentally kills Lee Harvey Oswald, saving Kennedy's life. Three years later in an alternate reality, it is revealed that through a series of chain events, the USSR won the Space Race and put the first man on the moon, meaning that the Dwarfers never travelled into deep space in the first place, trapping in an alternate 1966. The Dwarfers manage to correct this by trying to make Oswald shoot from a different floor, before making a impeached Kennedy assassinate himself, as the man on the grassy knoll.

Philip K. Dick also explored timeline corruption paradoxes. In the story "Orpheus with Clay Feet" Slade, a character from the future, goes on a time travel vacation to the past where he can visit famous science fiction writer Jack Dowland and become his muse. Slade, however, fails to inspire Dowland as he had hoped, and Dowland never becomes the master he should have been.

In the videogame World of Warcraft, the Bronze Dragonflight (tasked with the safety of the timelines) frequently asks the heroes(players) to help them fight the Infinite Dragonflight, who would want to change important events of the past. Although this may vary depending on the point of the view of the player, most of the events are negative ones - Thrall's escape from his prison, leading to the formation of the new Horde, enemies of the Alliance, then The Opening of the Dark portal, in which a corrupted Medivh opens up a link with the world of Draenor, starting the orcish invasions of Azeroth and ensuing wars, and the Culling of Stratholme, a defining moment in which Prince Arthas fall to madness leads to the rise of the undead Scourge and his eventual merge with the Lich king, they insist that the outcome of preventing such events would be much worse.

Multiple universes hypothesis

Another hypothesis is that there are an infinite number of universes, one for each possibility. Here, should the time traveller kill his grandfather, one universe would have a live grandfather, and another universe would have a dead one. Failing that, the universe would annihilate itself, for such a paradox would defy its laws.

Another theory concerning the classic grandfather paradox is that such an event would create a new universe, one in which the aforementioned deed was committed. This would not affect the committer's universe, nor the committer himself.

In The Legend of Zelda: Ocarina of Time, Link, having defeated the antagonist, Ganondorf, travels back in time to warn people about the events of the future. His actions prevent Ganondorf from taking over, seemingly changing the course of history. Unbeknownst to Link, the original, war ravaged timeline he left remained parallel to the peaceful one he created when he traveled back in time.

An example of this occurs in the Japanese anime series Dragonball Z in which Trunks, the son of Vegeta and Bulma comes to the present from the future. In the present, Trunks wasn't even born. He warns of the arrival of androids which are more powerful than even Goku and Vegeta, and forewarns the death of Goku in his past. However, by giving the medicine which can cure Goku and undertaking extensive training, Trunks and the Z Fighters manages to defeat the androids as well as Cell. When Trunks goes back to his present age though, his universe is still the same with Goku and other Z-fighters still dead, the only difference being that at that point of time, Trunks, because of his training with the Z-fighters, had become strong enough to defeat the androids and cell of his own time.

This was also in a DC anthology, which included among other series, one comic with Superman. In the comic, Superman attempted to change many of the world's great events, including Lincoln's assassination. When he came back to his own time, nothing had changed, but later he found a parallel version of the world with the altered history.

Temporal merging hypothesis

This is the opposite of the multiple universes hypothesis, in that each action committed in time travel actually overlaps one reality with another. For instance, if a time traveler were to meet his double from another time, the double would merge with the time traveler, making the traveler a part of the time he is visiting. The same would hold true for events. Two events would merge into the nearest event which does not produce a paradox (a dead grandfather in one universe but not in another would either create a dead grandfather in both universes, but alter the person's heritage so as to allow this, merge both timelines so that the person would fade from all timelines upon return, or produce a mean between life and death such as a coma).

An example of this is seen in the film The One, in which a character travels across time or dimensions, destroying copies of himself to cause them to merge — thus increasing power for the original character.

Choice timeline hypothesis

In the choice timeline hypothesis, history changes the instant the time traveler decides to travel back in time, thereby rendering his actions in that regard pre-destined.

Bill & Ted's Excellent Adventure, as well as its sequel and animated adaptation, feature numerous uses of this hypothesis. Bill and Ted, constantly realizing that their plans are foiled by the lack of a certain item, decide to later travel back in time and deliver themselves the necessary item, often indicating a specific place in which the item will appear. Upon searching the location, the item is invariably there.

Can-Not Because Has-Not theory

This theory states that the present is not the forefront of time, and so we are our future selves' past. Thus, if sometime in the future a time travel device were created, someone from the future would have already brought it back to us, thus establishing itself as "already" existing in our time as a result - and likely copied and recopied. Since our present selves are still wondering about time travel, this theory states that we will never be able to build a time machine, because if we are still wondering, then no one from the future has built a time machine and brought it back with them to us, and if no one in the future has built a time machine, then we in the future will not build a time machine, and no one can ever build a time machine because no one in the future has built one. This theory, however, creates a Causality Loop. Also if it is that any time machine made will allow only one way travel, i.e. into the future, or if it is that we can go into the future, but while returning, we can only return to the present (i.e. not set the dial to go back more than we used to go into the future, or before the time machine is invented), this theory fails. There are also other possibilities: someone in the future will build a time machine and many people will use it to travel back in the past, but we don't know this because: "no one can travel so far in the past to reach our time" or "no one has revealed that time-travelling is possible" or "no one that revealed that time-travelling is possible, was trusted" or "anyone with the knowledge to sufficiently understand temporal mechanics enough to build such a device, will also be enlightened enough not to interfere with the known written past" or "the time machine will be destroyed if you go back before it is created."

Temporal Disinterest Hypothesis

This hypothesis states that if someone builds a time machine for a specific purpose, and fulfills this purpose by means of time travel into the past, the resulting being (the maker of the time machine) would be satisfied and not have a reason to create a time machine, thus causing yet another paradox. This type of paradox is avoided in the 2002 adaptation of H.G. Wells' The Time Machine where the main character creates a time machine to save his dead fiance, but upon doing so she is killed another way. When traveling to the future he finally finds out that if she did not die he would never create the time machine, thus it is impossible to save her. Even though this does not create a physical paradox, it creates a mental one in which the time traveler who still builds the time machine for the same reason, remembers a different cause for that reason/outcome.

Harmony Theory

This teleological theory suggests that the universe tends toward harmony and will correct itself even if a person, event or idea “destroys” any one particular timeline. For example, if one were to create a time machine, travel back in time and kill Hitler before his rise to power in an effort to save the lives of six million Jews, the Holocaust would nevertheless have to happen—even without Hitler's presence—because in our universe, the events of World War II, including the Holocaust, must take place in order for the United States to become a superpower and use its influence to help create the United Nations, which in turn helped create the modern state of Israel. Some see an example of Harmony Theory in the fact that Isaac Newton and Gottfried Leibniz—without any overtly obvious connection—both invented infinitesimal calculus independently of one another. Another example of Harmony Theory might be seen in The Hitchhiker's Guide to the Galaxy, in which two pan-dimensional creatures expect Arthur Dent's brain to know the answer to the Ultimate Question to Life, the Universe, and Everything because it should already be in his thought patterns.

See also

• Causality
• Chaos theory
• Cosmic censorship hypothesis
• Time loop
• Grandfather paradox
• Ontological paradox
• Predestination paradox
• Retrocausality
• Science fiction
• Time travel
• Wormhole