David Lewis: You look a little blue. Wasn't Heaven what you expected? Pietro: We're not supposed to be here at all. The dogs tell their story. Lewis: Time paradoxes! You gotta be kidding me! Pietro: What? Lewis:You see: Time has either several dimensions, which would mean that time-travel could place you in other possible worlds. That would be weird, but not paradoxical. Or time has only one dimension. But in that case the seeming paradoxes are just instances of the time-traveller's subjective chronology differing from the objective one. Bissy: But in that case... Pietro: ...none of this can have happened! Logan: What?