  We prove a structure theorem for compact aspherical Lorentz manifolds with
abundant local symmetry. If M is a compact, aspherical, real-analytic, complete
Lorentz manifold such that the isometry group of the universal cover has
semisimple identity component, then the local isometry orbits in M are roughly
fibers of a fiber bundle. A corollary is that if M has a dense local isometry
orbit then M is locally homogeneous. The main result is analogous to a theorem
of Farb and Weinberger on compact aspherical Riemannian manifolds, and an
exposition of their arguments on rational cohomological dimension is included.
Some aspects of dynamics on Lorentz manifolds are also presented, including
totally geodesic, lightlike, codimension-one foliations associated to unbounded
sequences of isometries.
