Temporal paradox

A temporal paradox, time paradox, or time travel paradox, is an apparent or actual contradiction associated with the idea of time travel or other foreknowledge of the future. Temporal paradoxes arise from circumstances involving hypothetical time travel to the past. They are often employed to demonstrate the impossibility of time travel. Temporal paradoxes fall into three broad groups: bootstrap paradoxes, consistency paradoxes, and free will causality paradoxes exemplified by the Newcomb paradox.

Causal loop

A causal loop, also known as a bootstrap paradox, information loop, information paradox, or ontological paradox, occurs when any event, such as an action, information, an object, or a person, ultimately causes itself, as a consequence of either retrocausality or time travel. A causal loop appears to violate causality by allowing future events to influence the past and cause themselves. This is sometimes called "bootstrapping", which derives from the idiom "pull oneself up by one's bootstraps."

Backward time travel would allow information, people, or objects whose histories seem to "come from nowhere". Such causally looped events then exist in spacetime, but their origin cannot be determined. The notion of objects or information that are "self-existing" in this way is often viewed as paradoxical. Sergey Krasnikov writes that both paradoxes, either information or an object looping through time, are the same; the primary apparent paradox is a physical system evolving into a state in a way that is not governed by its laws.