The Milky Way potential is time-dependent, filled with orbiting, massive substructure, and has no useful symmetries. The stars orbiting have not had time to fully mix in phase space. Is inference—of the dynamics from a snapshot of the kinematics—still possible in this worst of all possible worlds? I think it is and I gave some hints about it today in the last of my workshop-like seminars.
[Going on vacation now for almost a month.]