 where the \(\left|c_i\right|\) are distinct groups of trajectories A. The form Eq. (\ref{eq:wharton}), according to Wharton, invites an interpretation of the probability in terms of ignorance concerning the actual group of trajectories \(c_i\), and he tentatively proposes a field interpretation of the \(c_i\). The interpretation is retrocausal because the probabilities over groups of trajectories are influenced by the future measurement time and setting. Open questions for this approach concern the grouping of trajectories, which is so far inherently ambiguous, the details of the suggested field interpretation, as well as generalizations to many-particle and other more general settings.