Strong cosmic censorship: taking the rough with the smooth

Understand

It has been argued that the strong cosmic censorship conjecture is violated by Reissner-Nordstr\"om-de Sitter black holes: for near-extremal black holes, generic scalar field perturbations arising from smooth initial data have finite energy at the Cauchy horizon even though they are not continuously differentiable there.

• In this paper, we consider the analogous problem for coupled gravitational and electromagnetic perturbations.
• We find that such perturbations exhibit a much worse violation of strong cosmic censorship: for a sufficiently large near-extremal black hole, perturbations arising from smooth initial data can be extended through the Cauchy horizon in an arbitrarily smooth way.
• This is in apparent contradiction with an old argument in favour of strong cosmic censorship.