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.