 The second type of response is to modify the transactional interpretation. For instance, Cramer (2016) introduces the idea of a hierarchy of advanced-wave echoes dependent upon the magnitude of the spatiotemporal interval from which they originate. Kastner (2013) surmises that the source of the problem that Maudlin has exposed, however, is the idea that quantum processes take place in the “block world”, and rejects this conception of processes in her own development of the transactional interpretation. According to her “possibilist” transactional interpretation, all the potential transactions exist in a real space of possibilities, which amounts at once to a kind of modal realism and an indeterminacy regarding future states of the system (hence Kastner’s rejection of the block universe view). The possibilist transactional interpretation arguably handles multi-particle scenarios more naturally, and presents the most modern sustained development of the transactional interpretation (although see P. Lewis 2013 for criticisms of the possibilist transactional interpretation specific to Maudlin’s challenge).