Time Travel & the Predestination Paradox Explained

Time Travel & the Predestination Paradox Explained

A Predestination Paradox refers to a phenomenon in which a person traveling back in time becomes part of past events, and may even have caused the initial event that caused that person to travel back in time in the first place. In this theoretical paradox of time travel, history is presented as being unalterable and predestined, with any attempts to change past events merely resulting in that event being fulfilled.

Science fiction has provided fertile ground for exploring this paradox of time travel, and over the years has provided much entertainment in the form of countless books and movies on the subject, some of which are mentioned in this article.

Etymology of Predestination Paradox

Origin of the term ‘Predestination’

The word ‘predestination’ derives from the Greek word “proorizo” with “pro” meaning “before” and the verb “orizo” meaning to “determine”. It has been in use since classical times, with the Greek physician Hippocrates (460-370 BC) using it to describe an intended result following the administration of medication. It is mentioned four times in the Bible, or more specifically in the Epistles of Paul, and over time in theology has come to represent God having immutably determined all events throughout eternity that will come to pass.

Origin of the term ‘Predestination Paradox’

The concept of a predestination paradox has been explored by scientific writers in the past, most notably by Robert A. Heinlein in his short stories entitled “By His Bootstraps” (1941) and “All You Zombies” (1959). However, it was the Star Trek franchise that coined the phrase “Predestination Paradox” in a 1996 episode of Star Trek: Deep Space Nine episode titled “Trials and Tribble-ations”.

The Deep Space Nine episode Trials and Tribble-ations was a homage to Star Trek the Original Series, and involves agents from Starfleet’s Department of Temporal Investigations visiting DS-9. The Department are there to determine whether the timeline has been corrupted after Captain Sisko took the USS Defiant back in time 105 years to save Captain James T. Kirk from being assassinated. The expression Predestination Paradox is used twice throughout the show. The first time is by two time agents who are questioning Captain Sisko while trying to establish his motive for traveling back in time:

LUCSLY: “So you’re not contending it was a predestination paradox?”
DULMUR: “A time loop. That you were meant to go back into the past?”

In the second instance, Doctor Bashir worries that after being invited on a date by a woman bearing his great-grandmother’s name, Watley, he could be destined to fall in love with her and become his own great-grandfather, who no one had ever met. As a worried Bashir then ponders: “If I don’t meet with her tomorrow, I may never be born.”

What type of paradox is the Predestination Paradox?

Time travel paradoxes are generally categorized into either:

1) Closed Causal Loops: When an action resulting from time travel to the past ensures the fulfillment of a cause. Examples include the Bootstrap Paradox and Predestination Paradox.

2) Consistency Paradoxes: When an action resulting from time travel to the past stops the cause from ever happening. Examples include the Grandfather Paradox, Hitler Paradox, and Polchinski’s Paradox.

Consistency Paradoxes vs. Causal Loops

To highlight the difference further, consistency paradoxes like the Grandfather Paradox create timeline inconsistencies caused by actually being able to change the past, including killing your own grandfather, thereby preventing your own existence. This would result in an inconsistent and altered version of a past event.

A Predestination Paradox, on the other hand, results in an internally consistent version of history, albeit involving an event that appears to predate the time traveler’s initial decision to travel to the past.  A  chrononaut visiting the past to prevent someone from being killed may still ultimately fail, but they are still able to use their time machine to return to their own present and continue living their lives in a linear fashion.

What is a Time Loop?

Time loops, on the other hand, are a favorite trope of time travel movies in which a person becomes stuck in a certain period of time after which the loop resets and they must repeat the time cycle endlessly. It is unclear whether these loops would be possible in our universe.

Predestination Paradoxes involving Objects

In Predestination (2014), an intersex temporal agent who has undergone sexual reassignment surgery travels back in time to save his younger female self from falling in love and becoming pregnant by a mysterious male lover, who then disappears, completely ruining her life. Upon meeting his younger, female self, the time traveler subsequently falls in love and impregnates her, thus becoming the very stranger who caused all the heartache he traveled back in time to prevent.

As well as an example of a predestination paradox, the act of self-creation in which the time traveler is his own mother and father is an example of a bootstrap paradox, or a self-created entity (object, data, person) with no discernible point of origin.

A simpler predestination example involves a person traveling back in time to prevent a fire that broke out at a famous museum a century earlier resulting in the destruction of many valuable pieces of art, only to accidentally cause a kerosene lamp to fall, therefore creating the very fire that later motivated them to travel back in the first place. Likewise, a person traveling back in time to save a loved one from suffering a tragic death will be unable to save them from their fate as the event has already been determined.

– Movie Examples

In the 2002 remake of The Time Machine, the scientist Alex Hartdegen witnesses his girlfriend Emma being killed by a mugger looking to steal her engagement ring, after which Hartdegen devotes his life to building a time machine in order to change the past. Once completed, subsequent attempts to interfere with time sees Emma die under different circumstances, including being trampled by a horse, leading him to conclude that “I could come back a thousand times… and see her die a thousand ways.”

He then travels to the future to see whether scientists have discovered a solution on how to change the past, and during a conversation with the Über-Morlock in the distant future is told:

“You built your time machine because of Emma’s death. If she had lived, it would never have existed, so how could you use your machine to go back and save her? You are the inescapable result of your tragedy, just as I am the inescapable result of you.”

Other examples of predestination paradox movies involving physical time travel include the Terminator franchise (1984-2015), Back to the Future (1985), Bill and Ted’s Excellent Adventure (1989), Kate and Leopold (2001), Harry Potter and the Prisoner of Azkaban (2004), Timecrimes (2007), Looper (2012), and Interstellar (2014).

Finally, the movie 12 Monkeys (1995) also presents a worthy example, with the main protagonist James Cole traveling back thirty years in time to investigate a deadly plague that decimated humanity in 1996. During his investigation, he experiences flashbacks to when he was a boy and witnessed a man being shot at an airport, only at the end of the film becoming the very same man he witnessed being killed, while a younger version of himself in 1996 watches on from the airport.

Predestination Paradoxes involving Information

Instead of a person traveling back in time another type of predestination paradox involves information being sent from the future and causing a person to fulfill his part in an event yet to happen. Once again, any attempt to change either the past or future is doomed to ultimately fail.

Say, for instance, one day a man receives information from the future that he was fated to die from a heart attack. He subsequently takes up an active exercise regime in order to avoid his predestined fate but eventually ends up overexerting himself and dying from the very heart attack he set out to prevent. In another example, a person receives future information that they will die by drowning in the future, and so decides never to step foot off dry land. A decade later, her car falls off a collapsing bridge and she drowns in the river, having never learned to swim.

In both these examples, information from the future interacts with past events to form a causality loop, with both cause and effect running in a continuous circle. It is the fact that the information received from the future was truly known to occur that makes them examples of predestination paradoxes, though. Otherwise, it would just be a case of past events causing future actions.

– Literature and Movie Examples

The classic Greek tragedy Oedipus Rex (429 BC) includes a force beyond science component, as even the god Apollo warned King Laius about the supernatural curse placed on his family by King Pelops of Pisa.

The story centers around King Laius, Queen Jocasta and their son Oedipus, whom the oracle at Delphi prophecies will grow up to kill his father and marry his mother, thus bringing disaster on the city of Thebes. King Laius then leaves the infant on a mountainside side to die, which is subsequently found and raised by King Polybus and Queen Merope. After growing up, Oedipus learns of the prophecy and so leaves home to protect his adopted parents, but on his journey quarrels and kills a stranger (Laius), and after later saving the kingless Thebes from a monstrous Sphinx marries the king’s widow, Jocasta, thereby inadvertently fulfilling the prophecy.

In Star Wars Episode III: Revenge of the Sith (2005), Anakin Skywalker sees a premonition of the death of his wife Padmé Amidala while giving birth to Luke and Leia, leading him to turn to the Dark Side in an attempt to save his wife, ultimately causing her to lose the will to live, and die in childbirth.

Possible Solutions to the Predestination Paradox

In Predestination Paradox movies, the protagonist is usually depicted as helpless to change their fate either through a lack of free will, ignorance, or an external force seemingly controlling their actions and circumstances. This tallies with ‘Novikov’s self-consistency principle’ which asserts that a time traveler is constrained to only creating a consistent version of history. In other words, there must be zero probability of creating a time paradox.

According to another solution called the ‘timeline-protection hypothesis’, any attempts to change the timeline would result in a probability distortion being created to protect the timeline. Furthermore, a highly improbable event may occur in order to prevent a paradoxical, impossible event from taking place. The force which subsequently interferes with any attempts to alter past events may involve physical laws, fate, or even an improbable event.

A further possibility explored in sci-fi stories is that the time traveler is actually a willing participant in ensuring a paradox is maintained, such as in Predestination (2014), a movie inspired by the book All You Zombies (1959). In both instances, the time traveler not impregnating his younger transgender self would have resulted in him never having been born at all and therefore ceasing to exist.

History Must be Preserved

According to the Predestination Paradox, history is pre-written and anything interacting with past events will only be able to act in a consistent way that enables the already established past events to be preserved. One last classic example highlights this point nicely.

A person builds a time machine to prevent a loved one from being killed by a hit-and-run driver. After traveling to the past and driving to the scene of the crime, they accidentally run over their loved one and cause the very tragedy that they sought to prevent. They then flee the scene of the crime and return to their present and continue with their life knowing that history is pre-written, and that you cannot change an event in the past that has already taken place.

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