INHOMOGENEOUS UNIVERSES IN OBSERVATIONAL COORDINATES

Isotropic inhomogeneous dust universes are analysed via observational coordinates based on the past light cones of the observer's galactic w orldline. The field equations are reduced to a single first-order ODE in observational variables on the past light cone, completing the obse rvational integration scheme. This leads naturally to an explicit exac t solution which is locally nearly homogeneous (i.e. FRW), but at larg er redshift develops an inhomogeneity. New observational characterizat ions of homogeneity (FRW universes) are also given.