in which an event is among the causes of another event, which in turn is among the causes of the first-mentioned event.[3][4] Such causally-looped events then exist in spacetime, but their origin cannot be determined.
The notion of objects or information which are "self-existing" in this way is often viewed as paradoxical,[2] with several authors referring to a causal loop involving information or objects without origin as a bootstrap paradox,[6][7][8][9]:343 an information paradox,[6] or an ontological paradox.[10] The use of "bootstrap" in this context refers to the expression "pulling yourself up by your bootstraps" and to Robert A. Heinlein's time travel story "By His Bootstraps".