Temporal paradox

A temporal paradox is a logical contradiction that arises in scenarios permitting time travel or closed timelike curves. The canonical examples are the grandfather paradox, in which a time traveler prevents their own existence, and the bootstrap paradox, in which information or objects exist without origin. These paradoxes are not merely curiosities: they reveal that a spacetime permitting closed timelike curves cannot support the well-posed initial value problems on which causal physics depends.

The Novikov Self-Consistency Principle resolves temporal paradoxes by restricting histories to self-consistent solutions, while the Chronology Protection Conjecture resolves them by forbidding the causal structures that would permit them. Both approaches treat temporal paradox not as a logical puzzle but as a boundary condition on physical law — a signal that the spacetime geometry is incompatible with the requirements of determinate history.