retrocausality

Retrocausality is the idea that causal influences can propagate backward in time, such that events in the future can affect events in the past. In physics, retrocausal explanations aim to reconcile time-symmetric fundamental laws with the apparent unidirection of experienced time. Proponents typically argue that retrocausal influences, if they exist, do not allow macroscopic paradoxes or faster-than-light signaling and may be confined to microphysical processes.

Historically, retrocausality has been explored in interpretations of quantum mechanics. The Wheeler–Feynman absorber theory posits advanced waves traveling backward in time as part of a consistent electrodynamic description. Cramer's Transactional Interpretation envisions a time-symmetric exchange between retarded and advanced waves forming a quantum transaction that yields observed outcomes. Delayed-choice and quantum-eraser experiments are sometimes cited as supporting retrocausal readings, though they are also compatible with conventional quantum mechanics.

Critics argue that retrocausal accounts may introduce causal paradoxes, conflict with realism, or complicate locality and relativity. Most physicists regard quantum correlations as describable by standard quantum theory without invoking backward causation. No experimental evidence has demonstrated macroscopic retrocausality or controllable backward signaling; the idea remains an interpretation or research program rather than an established theory.

Related topics include time symmetry, CPT invariance, closed timelike curves, and nonlocality in quantum mechanics. Retrocausal frameworks continue to be discussed within physics and philosophy as a way to understand the foundations of time and causation.