Retrocausality

[3][page needed] Philosophical considerations of time travel often address the same issues as retrocausality, as do treatments of the subject in fiction, but the two phenomena are distinct.

"[17] Closed timelike curves (CTCs), sometimes referred to as time loops,[17] in which the world line of an object returns to its origin, arise from some exact solutions to the Einstein field equation.

[18] Although CTCs do not appear to exist under normal conditions, extreme environments of spacetime, such as a traversable wormhole or the region near certain cosmic strings, may allow their brief formation, implying a theoretical possibility of retrocausality.

Wheeler–Feynman absorber theory, proposed by John Archibald Wheeler and Richard Feynman, uses retrocausality and a temporal form of destructive interference to explain the absence of a type of converging concentric wave suggested by certain solutions to Maxwell's equations.

[21] Ernst Stueckelberg, and later Richard Feynman, proposed an interpretation of the positron as an electron moving backward in time, reinterpreting the negative-energy solutions of the Dirac equation.

[22] This time-reversal of anti-particles is required in modern quantum field theory, and is for example a component of how nucleons in atoms are held together with the nuclear force, via exchange of virtual mesons such as the pion.

"[25] The backwards-in-time point of view is nowadays accepted as completely equivalent to other pictures,[26] but it has nothing to do with the macroscopic terms "cause" and "effect", which do not appear in a microscopic physical description.

They treat the experiments demonstrating these correlations as being described from different reference frames that disagree on which measurement is a "cause" versus an "effect", as necessary to be consistent with special relativity.

[33] Hypothetical superluminal particles called tachyons have a spacelike trajectory, and thus can appear to move backward in time, according to an observer in a conventional reference frame.

Despite frequent depiction in science fiction as a method to send messages back in time, hypothetical tachyons do not interact with normal tardyonic matter in a way that would violate standard causality.

Specifically, the Feinberg reinterpretation principle means that ordinary matter cannot be used to make a tachyon detector capable of receiving information.

[36][37] Such results and their underlying theories have been rejected by the mainstream scientific community and are widely accepted as pseudoscience, although they continue to have some support from fringe science sources.