Bootstrap paradox
Encyclopedia
The bootstrap paradox is a paradox
of time travel
in which information or objects can exist without having been created. After information or an object is sent back in time, it is recovered in the present and becomes the very object/information that was initially brought back in time in the first place. Numerous science fiction
stories are based on this paradox, which has also been the subject of serious physics articles.
The term "bootstrap paradox" refers to the expression "pulling yourself up by your bootstraps
"; the use of the term for the time-travel paradox was popularized by Robert A. Heinlein
's story By His Bootstraps
(see below).
proposes that contradictory causal loops cannot form, but that consistent ones can.
However, a scenario can occur where items or information are passed from the future to the past, which then become the same items or information that are subsequently passed back. This not only creates a loop, but a situation where these items have no discernible origin. Physical items are even more problematic than pieces of information, since they should ordinarily age and increase in entropy according to the Second law of thermodynamics
. But if they age by any nonzero amount at each cycle, they cannot be the same item to be sent back in time, creating a contradiction.
Another problem is the "reverse grandfather paradox
", where whatever is sent to the past allows the time travel in the first place (such as saving your past self's life, or sending vital information about the time travel mechanism).
The paradox raises the ontological
questions of where, when and by whom the items were created or the information derived. Time loop logic operates on similar principles, sending the solutions to computation problems back in time to be checked for correctness without ever being computed "originally".
Whether or not a scenario described in this paradox would actually be possible, even if time travel itself were possible, is not presently known.
The bootstrap paradox is similar to, but distinct from, the predestination paradox
, in which individuals or information travel back in time and ultimately trigger events they already experienced in their own present. In the latter case, no information or matter 'appears out of thin air'.
's story "By His Bootstraps
", in which the protagonist is asked to go through a time portal by a mysterious stranger, a second stranger tries to stop him, and all three get into a fight which results in the protagonist being pushed through anyway. Ultimately, it is revealed that all three are the same person: the first visitor is his future self and the second an even older future self trying to prevent the loop from occurring. The bootstrap paradox here is in where and how the loop started in the first place. Heinlein's "—All You Zombies—" involves an even more convoluted time loop involving kidnapping, seduction, child abandonment and sex reassignment surgery
, resulting in the protagonist creating the circumstances where he becomes his own mother, father, son, daughter, forever-lost lover and kidnapper.
One example is in the American drama, Lost. John Locke is given a compass by Richard Alpert in 2007. He later is sent back in time about 60 years where he gives the compass back to Alpert, telling him to bring him the compass in 2007. The compass is the subject of the paradox here, it goes through this loop infinite times when the island is dislodged from time.
One of the most noted examples of the bootstrap paradox in fiction occurs in the film Somewhere in Time
, based on the Richard Matheson
novel Bid Time Return
. In the film, Christopher Reeve
's character is given a pocket watch by an old lady. He then goes back in time and gives the pocket watch to the old lady's younger self, played by Jane Seymour
, which prompts her to seek him out years in the future and give him the watch, resulting in the watch having no apparent origin.
The bootstrap paradox occurs several times in the Terminator franchise, perhaps most notably in the creation of the main villain Skynet
. In the first film, the Terminator
cyborg sent back in time to kill Sarah Connor is destroyed, but its components are salvaged to form the basis of Skynet, the artificially intelligent computer network that will, in the future, send it back in time on its murderous mission. The knowledge of how to create an artificially intelligent machine therefore has no ultimate source.
The current series of Doctor Who
features many examples of the bootstrap paradox, most constructed by writer and later showrunner Steven Moffat
. For example, in Moffat's 2007 episode "Blink
", the Doctor
records a message on film in 1969 in the form of half a conversation. The other half is filled in when Sally Sparrow views the film on DVD in 2007, which her friend Lawrence Nightingale transcribes. The full transcript, including the Doctor's portion, is eventually handed to the Doctor in 2008, but before he is sent back to 1969 from his subjective viewpoint, so he can use it in creating the message later. The contents of the conversation form a bootstrap paradox. The Doctor explains Sally's confusion by revealing that most people think of time like "a swift progression of cause to effect", when it's actually, "like a big ball of wibbly-wobbly, timey-wimey... stuff".
Physical paradox
A physical paradox is an apparent contradiction in physical descriptions of the universe. While many physical paradoxes have accepted resolutions, others defy resolution and may indicate flaws in theory...
of time travel
Time travel
Time travel is the concept of moving between different points in time in a manner analogous to moving between different points in space. Time travel could hypothetically involve moving backward in time to a moment earlier than the starting point, or forward to the future of that point without the...
in which information or objects can exist without having been created. After information or an object is sent back in time, it is recovered in the present and becomes the very object/information that was initially brought back in time in the first place. Numerous science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
stories are based on this paradox, which has also been the subject of serious physics articles.
The term "bootstrap paradox" refers to the expression "pulling yourself up by your bootstraps
Bootstrapping
Bootstrapping or booting refers to a group of metaphors that share a common meaning: a self-sustaining process that proceeds without external help....
"; the use of the term for the time-travel paradox was popularized by Robert A. Heinlein
Robert A. Heinlein
Robert Anson Heinlein was an American science fiction writer. Often called the "dean of science fiction writers", he was one of the most influential and controversial authors of the genre. He set a standard for science and engineering plausibility and helped to raise the genre's standards of...
's story By His Bootstraps
By His Bootstraps
"By His Bootstraps" is a science fiction short story by Robert A. Heinlein that plays with some of the inherent paradoxes that would be caused by time travel. It was originally published in the October 1941 issue of Astounding Science Fiction under the pen name Anson MacDonald...
(see below).
Definition
Because of the possibility of influencing the past while time traveling, one way of explaining why history does not change is to posit that these changes already are contained self-consistently in the past timeline. A time traveler attempting to alter the past in this model, intentionally or not, would only be fulfilling his or her role in creating history, not changing it. The Novikov self-consistency principleNovikov self-consistency principle
The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture, is a principle developed by Russian physicist Igor Dmitriyevich Novikov in the mid-1980s to solve the problem of paradoxes in time travel, which is theoretically permitted in certain solutions of general...
proposes that contradictory causal loops cannot form, but that consistent ones can.
However, a scenario can occur where items or information are passed from the future to the past, which then become the same items or information that are subsequently passed back. This not only creates a loop, but a situation where these items have no discernible origin. Physical items are even more problematic than pieces of information, since they should ordinarily age and increase in entropy according to the Second law of thermodynamics
Second law of thermodynamics
The second law of thermodynamics is an expression of the tendency that over time, differences in temperature, pressure, and chemical potential equilibrate in an isolated physical system. From the state of thermodynamic equilibrium, the law deduced the principle of the increase of entropy and...
. But if they age by any nonzero amount at each cycle, they cannot be the same item to be sent back in time, creating a contradiction.
Another problem is the "reverse grandfather paradox
Grandfather paradox
The grandfather paradox is a proposed paradox of time travel first described by the science fiction writer René Barjavel in his 1943 book Le Voyageur Imprudent . The paradox is this: suppose a man traveled back in time and killed his biological grandfather before the latter met the traveler's...
", where whatever is sent to the past allows the time travel in the first place (such as saving your past self's life, or sending vital information about the time travel mechanism).
The paradox raises the ontological
Ontology
Ontology is the philosophical study of the nature of being, existence or reality as such, as well as the basic categories of being and their relations...
questions of where, when and by whom the items were created or the information derived. Time loop logic operates on similar principles, sending the solutions to computation problems back in time to be checked for correctness without ever being computed "originally".
Whether or not a scenario described in this paradox would actually be possible, even if time travel itself were possible, is not presently known.
The bootstrap paradox is similar to, but distinct from, the predestination paradox
Predestination paradox
A predestination paradox 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...
, in which individuals or information travel back in time and ultimately trigger events they already experienced in their own present. In the latter case, no information or matter 'appears out of thin air'.
Involving information
- On his 30th birthday, a man who wishes to build a time machineTime travelTime travel is the concept of moving between different points in time in a manner analogous to moving between different points in space. Time travel could hypothetically involve moving backward in time to a moment earlier than the starting point, or forward to the future of that point without the...
is visited by a future version of himself. This future self explains to him that he should not worry about designing the time machine, as he has done it in the future. The man receives the schematics from his future self and starts building the time machine. Time passes until he finally completes the time machine. He then uses it to travel back in time to his 30th birthday, where he gives the schematics to his past self, closing the loop. - A professor travels forward in time, and reads in a physics journal about a new equation that was recently derived. She travels back to her own time, and relates it to one of her students who writes it up, and the article is published in the same journal which the professor reads in the future.
- A man builds a time machine. He goes into the future and steals a valuable gadget. He then returns and reveals the gadget to the world, claiming it as his own. Eventually, a copy of the device ends up being the item the man originally steals. In other words, the device is a copy of itself and it is not possible to state where the original came from.
- A young physicist receives an old, disintegrating notebook containing information about future events sent by her future self via a time machine; before the book deteriorates so badly as to be unusable, she copies the information in it into a new notebook. Over the years the predictions of the notebook come true, allowing her to become wealthy enough to fund her own research, which results in the development of a time machine, which she uses to send the now old, tattered, disintegrating notebook back to her former self. The notebook is not a paradox (it has an end and a beginning; the beginning where she receives it and the end where she threw it out after she copied the information), but the information is: it is impossible to state where it came from. The professor has transferred the information that she wrote herself, so there was no original notebook.
Involving physical items
- A woman is locked outside her house because she's lost her keys. Another woman approaches her with the keys. When the woman enters the house five minutes later, she encounters a time machine which transports her and her keys back in time five minutes, allowing her to give them to herself and close the loop. [The woman would have to take the keys she left inside back in time, otherwise the keys given to her would age by a non-zero amount.]
Involving people
- A man travels back in time and falls in love with and marries a woman, who he later learns was his own mother, who then gives birth to him. He is therefore his own father and, because of this, also his own grandfather, great-grandfather, great-great grandfather, great-great-great grandfather and so on, making his ancestry infinite, and also giving him no origin for his paternal genetic material.
Examples from fiction
The term bootstrap paradox comes from Robert A. HeinleinRobert A. Heinlein
Robert Anson Heinlein was an American science fiction writer. Often called the "dean of science fiction writers", he was one of the most influential and controversial authors of the genre. He set a standard for science and engineering plausibility and helped to raise the genre's standards of...
's story "By His Bootstraps
By His Bootstraps
"By His Bootstraps" is a science fiction short story by Robert A. Heinlein that plays with some of the inherent paradoxes that would be caused by time travel. It was originally published in the October 1941 issue of Astounding Science Fiction under the pen name Anson MacDonald...
", in which the protagonist is asked to go through a time portal by a mysterious stranger, a second stranger tries to stop him, and all three get into a fight which results in the protagonist being pushed through anyway. Ultimately, it is revealed that all three are the same person: the first visitor is his future self and the second an even older future self trying to prevent the loop from occurring. The bootstrap paradox here is in where and how the loop started in the first place. Heinlein's "—All You Zombies—" involves an even more convoluted time loop involving kidnapping, seduction, child abandonment and sex reassignment surgery
Sex reassignment surgery
Sex reassignment surgery is a term for the surgical procedures by which a person's physical appearance and function of their existing sexual characteristics are altered to resemble...
, resulting in the protagonist creating the circumstances where he becomes his own mother, father, son, daughter, forever-lost lover and kidnapper.
One example is in the American drama, Lost. John Locke is given a compass by Richard Alpert in 2007. He later is sent back in time about 60 years where he gives the compass back to Alpert, telling him to bring him the compass in 2007. The compass is the subject of the paradox here, it goes through this loop infinite times when the island is dislodged from time.
One of the most noted examples of the bootstrap paradox in fiction occurs in the film Somewhere in Time
Somewhere in Time (film)
Somewhere in Time is a 1980 romantic science fiction film directed by Jeannot Szwarc. It is a film adaptation of the 1975 novel Bid Time Return by Richard Matheson, who also wrote the screenplay...
, based on the Richard Matheson
Richard Matheson
Richard Burton Matheson is an American author and screenwriter, primarily in the fantasy, horror, and science fiction genres. He is perhaps best known as the author of What Dreams May Come, Bid Time Return, A Stir of Echoes, The Incredible Shrinking Man, and I Am Legend, all of which have been...
novel Bid Time Return
Bid Time Return
Bid Time Return is a 1975 science fiction novel by Richard Matheson. It concerns a man from the 1970s who travels back in time to court a 19th century stage actress whose photograph has captivated him...
. In the film, Christopher Reeve
Christopher Reeve
Christopher D'Olier Reeve was an American actor, film director, producer, screenwriter, author and activist...
's character is given a pocket watch by an old lady. He then goes back in time and gives the pocket watch to the old lady's younger self, played by Jane Seymour
Jane Seymour
Jane Seymour was Queen of England as the third wife of King Henry VIII. She succeeded Anne Boleyn as queen consort following the latter's execution for trumped up charges of high treason, incest and adultery in May 1536. She died of postnatal complications less than two weeks after the birth of...
, which prompts her to seek him out years in the future and give him the watch, resulting in the watch having no apparent origin.
The bootstrap paradox occurs several times in the Terminator franchise, perhaps most notably in the creation of the main villain Skynet
Skynet (Terminator)
Skynet is the main antagonist in the Terminator franchise—an artificially intelligent system which became self-aware and revolted against its creators...
. In the first film, the Terminator
Terminator (character concept)
In the Terminator film series, a terminator is an autonomous robot, typically humanoid, originally conceived as a virtually indestructible soldier and assassin, as well as an infiltrator....
cyborg sent back in time to kill Sarah Connor is destroyed, but its components are salvaged to form the basis of Skynet, the artificially intelligent computer network that will, in the future, send it back in time on its murderous mission. The knowledge of how to create an artificially intelligent machine therefore has no ultimate source.
The current series of Doctor Who
Doctor Who
Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a time-travelling humanoid alien known as the Doctor who explores the universe in a sentient time machine called the TARDIS that flies through time and space, whose exterior...
features many examples of the bootstrap paradox, most constructed by writer and later showrunner Steven Moffat
Steven Moffat
Steven Moffat is a Scottish television writer and producer.Moffat's first television work was the teen drama series Press Gang. His first sitcom, Joking Apart, was inspired by the breakdown of his first marriage; conversely, his later sitcom Coupling was based upon the development of his...
. For example, in Moffat's 2007 episode "Blink
Blink (Doctor Who)
"Blink" is the 10th episode of the third series of the new production of the British science fiction television series Doctor Who. It was first broadcast on 9 June 2007, and is the only episode in the 2007 series written by Steven Moffat; the episode is based on a previous short story written by...
", the Doctor
Doctor (Doctor Who)
The Doctor is the central character in the long-running BBC television science-fiction series Doctor Who, and has also featured in two cinema feature films, a vast range of spin-off novels, audio dramas and comic strips connected to the series....
records a message on film in 1969 in the form of half a conversation. The other half is filled in when Sally Sparrow views the film on DVD in 2007, which her friend Lawrence Nightingale transcribes. The full transcript, including the Doctor's portion, is eventually handed to the Doctor in 2008, but before he is sent back to 1969 from his subjective viewpoint, so he can use it in creating the message later. The contents of the conversation form a bootstrap paradox. The Doctor explains Sally's confusion by revealing that most people think of time like "a swift progression of cause to effect", when it's actually, "like a big ball of wibbly-wobbly, timey-wimey... stuff".
See also
- Grandfather paradoxGrandfather paradoxThe grandfather paradox is a proposed paradox of time travel first described by the science fiction writer René Barjavel in his 1943 book Le Voyageur Imprudent . The paradox is this: suppose a man traveled back in time and killed his biological grandfather before the latter met the traveler's...
- Newcomb's paradoxNewcomb's paradoxNewcomb's paradox, also referred to as Newcomb's problem, is a thought experiment involving a game between two players, one of whom purports to be able to predict the future. Whether the problem is actually a paradox is disputed....
- Predestination paradoxPredestination paradoxA predestination paradox 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...
- Self-fulfilling prophecySelf-fulfilling prophecyA self-fulfilling prophecy is a prediction that directly or indirectly causes itself to become true, by the very terms of the prophecy itself, due to positive feedback between belief and behavior. Although examples of such prophecies can be found in literature as far back as ancient Greece and...
- Strange loopStrange loopA strange loop arises when, by moving up or down through a hierarchical system, one finds oneself back where one started.Strange loops may involve self-reference and paradox...
- Temporal paradoxTemporal paradoxTemporal paradox is a theoretical paradoxical situation that happens because of time travel. A time traveler goes to the past, and does something that would prevent him from time travel in the first place...
- The chicken or the eggThe chicken or the eggThe Chicken or the egg causality dilemma is commonly stated as "which came first, the chicken or the egg?" To ancient philosophers, the question about the first chicken or egg also evoked the questions of how life and the universe in general began....
- Time travel in fictionTime travel in fictionTime travel is a common theme in science fiction and is depicted in a variety of media. It simply means either going forward in time or backward, to experience the future, or the past.-Literature:...