Temporal paradox

A temporal paradox, time paradox, or time travel paradox is a paradox, an apparent contradiction, or a logical contradiction that is associated with the idea of time and time travel. In physics, temporal paradoxes fall into two broad groups: consistency paradoxes exemplified by the grandfather paradox; and causal loops.[1] More broadly, a variation of the Fermi paradox also applies to time travel.

Causal loop

A causal loop is a paradox of time travel that occurs when a future event is the cause of a past event, which in turn is the cause of the future event. Both events then exist in spacetime, but their origin cannot be determined. A causal loop may involve an event, a person or object, or information.[1][2] The terms boot-strap paradox, predestination paradox or ontological paradox are sometimes used in fiction to refer to a causal loop.[3][4]

Grandfather paradox

The consistency paradox or grandfather paradox occurs when the past is changed in any way, thus creating a contradiction. A time traveller can do anything that did happen, but can't do anything that didn't happen. Doing something that didn't happen results in a contradiction.[2] Consistency paradoxes occur whenever changing the past is possible.[1]

Fermi paradox

The Fermi paradox can be adapted for time travel, and phrased "if time travel were possible, where are all the visitors from the future?" Answers vary, from time travel not being possible, to the possibility that visitors from the future can not reach any arbitrary point in the past, or that they disguise themselves to avoid detection.[5]

See also


  1. ^ a b c Francisco Lobo (2002). "Time, Closed Timelike Curves and Causality" (PDF). p. 2. Retrieved November 2, 2015.
  2. ^ a b Nicholas J.J. Smith (2013). "Time Travel". Stanford Encyclopedia of Philosophy. Retrieved November 2, 2015.
  3. ^ Leora Morgenstern (2010), Foundations of a Formal Theory of Time Travel (PDF), p. 6, retrieved November 2, 2015
  4. ^ Klosterman, Chuck (2009). Eating the Dinosaur (1st Scribner hardcover ed.). New York: Scribner. p. 60. ISBN 9781439168486. Retrieved 2 February 2013.
  5. ^ "Carl Sagan Ponders Time Travel". NOVA. PBS. December 10, 1999. Retrieved April 26, 2017.
Asylum (Darvill-Evans novel)

Asylum is a BBC Books original novel written by Peter Darvill-Evans and based on the long-running British science fiction television series Doctor Who. It features the Fourth Doctor and Nyssa (resulting in a slight temporal paradox as the Nyssa featured here comes from a time some time after she stopped travelling with the Fifth Doctor).

Christmas Guy

"Christmas Guy" is the eighth episode of the twelfth season of the animated comedy series Family Guy and the 218th episode overall. It aired on Fox in the United States and Canada on December 15, 2013, and is written by Patrick Meighan and directed by Greg Colton.The episode features the return of Brian Griffin (who had died two episodes earlier in "Life of Brian") after Stewie goes back in time to save him.

Decision 3012

"Decision 3012" is the third episode of the seventh season of the animated sitcom Futurama. It originally aired on Comedy Central on June 27, 2012. The plot is a parody of the Birther Movement.

Grandfather paradox

The grandfather paradox is a paradox of time travel in which inconsistencies emerge through changing the past. The name comes from the paradox's common description: a person travels to the past and kills their own grandfather before the conception of their father or mother, which prevents the time traveller's existence. Despite its title, the grandfather paradox does not exclusively regard the contradiction of killing one's own grandfather to prevent one's birth. Rather, the paradox regards any action that alters the past, since there is a contradiction whenever the past becomes different from the way it was.


Koparion is a genus of small coelurosaurian theropod dinosaurs (probably troodontids), from the late Jurassic Period (Kimmeridgian stage), of Utah. It contains the single named species Koparion douglassi which is known only from a single isolated tooth.

Millennium (novel)

Millennium is a 1983 science fiction novel by John Varley. Varley later turned this novel into the script for the 1989 film Millennium, both of which are based on Varley's short story "Air Raid", which was published in 1977. It was nominated for the Philip K. Dick Award in 1983, and for both the Hugo and Locus Awards in 1984.


A paradox is a statement that, despite apparently valid reasoning from true premises, leads to an apparently-self-contradictory or logically unacceptable conclusion. A paradox involves contradictory-yet-interrelated elements that exist simultaneously and persist over time.Some logical paradoxes are known to be invalid arguments but are still valuable in promoting critical thinking.Some paradoxes have revealed errors in definitions assumed to be rigorous, and have caused axioms of mathematics and logic to be re-examined. One example is Russell's paradox, which questions whether a "list of all lists that do not contain themselves" would include itself, and showed that attempts to found set theory on the identification of sets with properties or predicates were flawed. Others, such as Curry's paradox, are not yet resolved.

Examples outside logic include the ship of Theseus from philosophy (questioning whether a ship repaired over time by replacing each and all of its wooden parts, one at a time, would remain the same ship). Paradoxes can also take the form of images or other media. For example, M.C. Escher featured perspective-based paradoxes in many of his drawings, with walls that are regarded as floors from other points of view, and staircases that appear to climb endlessly.In common usage, the word "paradox" often refers to statements that are ironic or unexpected, such as "the paradox that standing is more tiring than walking".


Pre-crime (or precrime) is a term coined by science fiction author Philip K. Dick. It is increasingly used in academic literature to describe and criticise the tendency in criminal justice systems to focus on crimes not yet committed. Pre-crime has been defined as "substantive coercive state interventions targeted at non-imminent crimes". Pre-crime intervenes to punish, disrupt, incapacitate or restrict those deemed to embody future crime threats. The term pre-crime embodies a temporal paradox, suggesting both that a crime has not occurred and that the crime that has not occurred is a foregone conclusion (McCulloch and Wilson 2016).


'Temporal' can refer to time, or to material existence and secularity, or to the temple in anatomy. Below is a list of possible uses.

Temporal (video game)

Temporal is a freeware videogame featuring platform and puzzle elements. The game was created by Israeli developer Oren Bartal using the Allegro library.

Temporal paradox (paleontology)

The temporal paradox, or time problem is a controversial issue in the evolutionary relationships of birds. It was described by paleornithologist Alan Feduccia in 1994. It reflects a conflict between where chronologically fossils are expected to be found based on a proposed phylogeny, and where they are actually found. The temporal paradox can give rise to alternative phylogenies (i.e. the archosaurian hypothesis of bird evolution).

Statistical measures have been devised to assess the likelihood of proposed phylogenies based on the size and positioning of gaps in the fossil record.

The Clock that Went Backward

"The Clock That Went Backward" is a fantasy short story by Edward Page Mitchell.

The Constant

"The Constant" is the fifth episode of the fourth season of the American Broadcasting Company's (ABC) serial drama television series Lost, and the 77th episode overall. It was broadcast on February 28, 2008, on ABC in the United States and on CTV in Canada. It was written by executive producer Carlton Cuse and co-creator/executive producer Damon Lindelof and directed by executive producer Jack Bender. "The Constant" was watched by 15 million American viewers and is widely regarded as one of Lost's best episodes. It was nominated for three Primetime Emmy Awards, a Directors Guild of America Award, and a Hugo Award.

In the episode, Desmond Hume (played by Henry Ian Cusick) and Sayid Jarrah (Naveen Andrews) are being flown by Frank Lapidus (Jeff Fahey) to the freighter where Lapidus' mission is set. After going through turbulence, Desmond's consciousness unexpectedly travels through time between 1996 and 2004. The helicopter reaches the freighter and Sayid and Desmond are introduced to communications officer George Minkowski (Fisher Stevens), who is "unstuck in time" like Desmond. The writers took twice the time expected to develop the episode's script; the biggest concern was the avoidance of a temporal paradox when dealing with time travel.

The End of Eternity

The End of Eternity is a 1955 science fiction novel by American writer Isaac Asimov, with mystery and thriller elements on the subjects of time travel and social engineering. Its premise is that of a causal loop – a type of temporal paradox in which events and their causes form a loop.

In The End of Eternity, members of the time-changing organization Eternity seek to ensure that their own organization is founded as history says it was, by ensuring the conditions for that event happen as history says they happened. The protagonist, Andrew Harlan, is placed in a situation where he must decide whether to allow the "circle" to close and Eternity be founded, or to allow the opposite to happen and Eternity never to have existed.

Many years later, Asimov tied this novel into his broader Foundation Series, by hinting in Foundation's Edge that it is set in a universe where Eternity had existed but was destroyed by Eternals, leading to an all-human galaxy later.

The novel was shortlisted to the Hugo Award for Best Novel.

The Menace from Earth (short story collection)

The Menace From Earth is a collection of science fiction short stories by American writer Robert A. Heinlein. It was published by The Gnome Press in 1959 in an edition of 5,000 copies.

The Witches of Chiswick

The Witches Of Chiswick is a novel by the British author Robert Rankin, the title parodying that of The Witches of Eastwick by John Updike.

Tikka to Ride

"Tikka To Ride" is the first episode of science fiction sitcom Red Dwarf Series VII and the 37th in the series run. It was first broadcast on the British television channel BBC2 on 17 January 1997. Written by Doug Naylor and directed by Ed Bye, it was the first episode not to involve co-creator and writer Rob Grant.

Series VII was the first series to have extended episodes.

Touched by an Angel (novel)

Touched by an Angel is a BBC Books original novel written by Jonathan Morris and based on the long-running British science fiction television series Doctor Who. It features the Eleventh Doctor, and his Companions Amy Pond and Rory Williams.

The story is about a girl called Rebecca Whitaker who dies in a car accident. Her husband Mark is still grieving years on and when he is sent back in time by a Weeping Angel, he attempts to stop her dying. The Doctor, Amy and Rory track him down and try to stop him before he creates a paradox.

General terms and concepts
Time travel in fiction
Temporal paradoxes
Parallel timelines
Philosophy of space and time
Spacetimes in general relativity that
can contain closed timelike curves

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