Temporal paradox

This article is about logical problems involved in the concept of time travel. For the controversy over the origin of birds, see temporal paradox (paleontology).

"Time paradox" redirects here. For the 2008 fantasy novel, see Artemis Fowl: The Time 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. Temporal paradoxes fall into two broad groups: consistency paradoxes exemplified by the grandfather paradox; and causal loops.

Causal loop

Main article: 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. A causal loop is also known as a boot-strap paradox, predestination paradox or ontological paradox in fiction.

Grandfather paradox

Main article: grandfather paradox

The consistency paradox or grandfather paradox occurs when a future event prevents the occurrence of a past event that was partly or entirely the cause of the future event, thereby preventing the future event from occurring, thus creating a contradiction. Consistency paradoxes occur whenever changing the past is possible.

See also

• Cosmic censorship hypothesis
• Retrocausality
• Wormhole