Time Travel and Coherence: Proper-Time Asymmetry, Closed Timelike Curves, and the Instantiation Filter

Time travel is commonly discussed as if “going to the future” (relativistic time dilation) and “going to the past” (closed timelike curves, wormholes) were variations of a single phenomenon. They are not. This paper distinguishes (i) proper-time asymmetry within a single spacetime history from (ii) past-directed history alteration, which would require global self-consistency across causes, records, and instantiated identities. We argue that forward time dilation is coherent and empirically realized, while past-directed travel is constrained by either (a) physical chronology protection or (b) a coherence-based instantiation filter. Scenarios that require global re-instantiation of the universe’s state to accommodate an inserted agent are generically non-instantiable, because they violate stable identity conditions and record consistency. The result is a bounded imagination thesis: human conceivability exceeds physical admissibility. Not everything the mind can describe corresponds to a coherent, record-supporting spacetime history.