  An algebraic characterization of vacuum states in Minkowski space is given
which relies on recently proposed conditions of geometric modular action and
modular stability for algebras of observables associated with wedge-shaped
regions. In contrast to previous work, continuity properties of these algebras
are not assumed but derived from their inclusion structure. Moreover, a unique
continuous unitary representation of spacetime translations is constructed from
these data. Thus the dynamics of relativistic quantum systems in Minkowski
space is encoded in the observables and state and requires no prior assumption
about any action of the spacetime symmetry group upon these quantities.
