Abstract
The global geometry of manifolds endowed with a semi-Riemannian (i.e.,m non positive definite) metric tensor is quite different from the Riemannian case. For instance, compact Lorentz manifolds may fail to be geodesically complete or geodesically connected. Moreover, their isometry group may fail to be compact.On the other hand, Lorentz manifolds that admitr a somewhere timelike Killing v…