Philosophical resolutions to time‑travel paradoxes invoke either the Novikov self‑consistency principle (only self‑consistent histories are allowed) or the many‑worlds interpretation (each action spawns a new branch).

The grandfather paradox—where a traveler prevents their own birth—appears to make backward time travel logically impossible. Philosopher David Lewis (1976) argued that time travel is compatible with causality if the traveler's actions are always consistent with the history they encounter; they cannot change the past but can participate in it. Physicist Igor Novikov formalized this as the self‑consistency principle: the laws of physics restrict CTCs to only those trajectories that produce no contradictions. Alternatively, Hugh Everett's many‑worlds view suggests that any action in the past creates a divergent branch of reality, leaving the original timeline unchanged. Both approaches preserve logical coherence, though they imply radically different ontologies about the nature of time and freedom.