In an irrotational dust universe, the locally free gravitational field is covariantly described by the gravito-electric and gravito-magnetic tensors E ab and H ab . In Newtonian theory, H ab = 0 and E ab is the tidal tensor. Newtonian-like dust universes in general relativity (i.e. with H ab = 0, often called 'silent') have been shown to be inconsistent in general and unlikely to extend beyond the known spatially homogeneous or Szekeres examples. Furthermore, they are subject to a linearization instability. Here we show that 'anti-Newtonian' universes, i.e. with purely gravito-magnetic field, so that E ab = 0 = H ab , are also subject to severe integrability conditions. Thus these models are inconsistent in general. We show also that there are no anti-Newtonian spacetimes that are linearized perturbations of Robertson-Walker universes. The only E ab = 0 = H ab solution known to us is not a dust solution, and we show that it is kinematically Gödel-like but dynamically unphysical.PACS numbers: 0420, 9880, 9530
IntroductionIrrotational dust spacetimes are characterized by vanishing pressure (p = 0) ‡ and vorticity (ω a = 0), and positive energy density (ρ > 0). They are important arenas for studying both the late universe [1,2] and gravitational collapse models [3]. Apart from the spatially homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) case, which is characterized by vanishing shear (σ ab = 0), these spacetimes have non-zero shear and non-zero locally free gravitational field. This field is represented by the irreducible electric and magnetic parts E ab and H ab of the Weyl tensor (see [4] for a covariant analysis of local freedom in the gravitational field). ‡ It is implicit that the anisotropic stress π ab and the energy flux q a also vanish. § A weaker covariant condition for the absence of gravitational radiation is that the spatial curls (defined below) of E ab and H ab must vanish [7,8,4].