  A method is proposed for constraining the Galactic gravitational potential
from high precision observations of the phase space coordinates of a system of
relaxed tracers. The method relies on an "ergodic" assumption that the
observations are representative of the state of the system at any other time.
The observed coordinates serve as initial conditions for moving the tracers
forward in time in an assumed model for the gravitational field. The validity
of the model is assessed by the statistical equivalence between the
observations and the distribution of tracers at randomly selected times. The
applicability of this ergodic method is not restricted by any assumption on the
form or symmetry of the potential. However, it requires high recision
observations as those that will be obtained from missions like SIM and GAIA.
