retrocausal

Retrocausality (or retrocausal) refers to the idea that causal influences can propagate backward in time, from future events to past events. In physics, retrocausal explanations are typically explored as time-symmetric or bidirectional accounts of influence that aim to reconcile certain quantum phenomena with locality and realistic descriptions of physical systems. This does not automatically imply the possibility of controllably sending information to the past; most retrocausal proposals preserve the prohibition on faster-than-light signaling at the macroscopic level.

In quantum mechanics, retrocausal approaches are associated with time-symmetric formulations such as the two-state vector formalism, developed by Yakir Aharonov and colleagues, which posits that quantum systems are described by both forward-evolving and backward-evolving states. Proponents argue that future measurement choices can play a role in determining past properties, offering a way to account for correlations without invoking nonlocal causation. Related ideas appear in interpretations influenced by the Wheeler–Feynman absorber theory in electrodynamics, which uses advanced (future-directed) and retarded (past-directed) waves within a time-symmetric framework.

Retrocausality is a controversial topic. Critics contend that retrocausal explanations risk introducing paradoxes or conflicts with established notions of causality, determinism, and free will, and that they may be difficult to test unambiguously. Most mainstream interpretations of quantum mechanics remain agnostic or skeptical about retrocausality, often favoring views that avoid backward-in-time influences altogether. Nevertheless, retrocausal ideas continue to be explored as one of several interpretive approaches to understanding quantum correlations and the foundations of time.