REISSNER-NORDSTROM-DE-SITTER METRIC, THE 3RD LAW, AND COSMIC CENSORSHIP

The essential features of the Reissner-Nordström-de Sitter metric are examined in relation to the third law of black-hole mechanics and the cosmic censorship hypothesis for a nonasymptotically flat situation. The evolution of thin charged dust shells in this metric shows that the thermodynamic character of cosmological event horizons differs from that of black-hole horizons in that a degenerate horizon can be produced in a finite time. Nonetheless the spirit of the third law is preserved since the resultant degenerate configurations do not represent physically attainable limits in our Universe. It is shown that the nakedly singular character of the analytic extensions to these solutions represents an unphysical idealization due to the inherent instability of Killing horizons to the past of their bifurcation. This adds support to the spirit of strong cosmic censorship. © 1979 The American Physical Society.