Seth Lloyd proposed an alternative approach to time travel with closed timelike curves (CTCs), based on " post-selection " and path integrals. Path integrals are a powerful tool in quantum mechanics that involve summing probabilities over all possible ways a system could evolve, even if those paths don't strictly follow a single timeline. Unlike classical approaches, path integrals allow for consistent histories even with CTCs. Lloyd argues that focusing on the state of the system outside the CTC is more relevant.