DYNAMICS OF SILENT UNIVERSES

We investigate the local nonlinear dynamics of irrotational dust with vanishing magnetic part of the Weyl tensor, H-ab. Once coded in the in itial conditions, this dynamical restriction is respected by the relat ivistic evolution equations. Thus, the outcome of the latter are exact solutions for special initial conditions with H-ab = 0, but with no s ymmetries: they describe inhomogeneous triaxial dynamics generalizing that for a fluid element in a Tolman-Bondi, Kantowski-Sachs, or Szeker es geometry. A subset of these solutions may be seen as (special) pert urbations of Friedmann models, in the sense that there are trajectorie s in phase-space that pass arbitrarily close to the isotropic ones. We find that the final fate of ever-expanding configurations is a spheri cal void, locally corresponding to a Milne universe. For collapsing co nfigurations we find a whole family of triaxial attractors, with vanis hing local density parameter Omega. These attractors locally correspon d to Kasner vacuum solutions: only a set of measure zero of physical c onfigurations collapses to a degenerate pancake, while the generic con figuration collapses to a triaxial spindle singularity. These silent u niverse models may provide a fair representation of the universe on su perhorizon scales. Moreover, one might conjecture that the nonlocal in formation carried by H-ab becomes negligible during the late highly no nlinear stages of collapse, so that the attractors we find may be all those relevant for expanding or collapsing configurations of irrotatio nal dust.