19 - Relativistic cosmology IV: simple generalisations of L–T and related geometries

Summary

The plane- and hyperbolically symmetric counterparts of the L–T models (i.e. the Ellis solutions), and generalisations of all three classes to charged dust source are derived and discussed. It is shown that the most natural interpretation of the plane-symmetric Ellis metric is an expanding or contracting family of 2-dimensional flat tori. The proof of the Ori theorem that for a spherically symmetric weakly charged dust ball shell crossings will block the bounce through the minimal radius is copied in detail. A subcase left out by Ori is discussed, but it will also lead to a shell crossing, only at the other side of the minimal radius. In this special case, a peculiar direction-dependent singularity is present: at the centre the matter density becomes negative for a short period before and after the bounce. The Datt–Ruban solution, its generalisation to charged dust source and the matching of both these solutions to, respectively, the Schwarzschild and Reissner–Nordstr\“{o}m solutions are presented and discussed. In the matched configuration the DR region stays inside the Schwarzschild or RN event horizon.