The statement that general relativity is deterministic finds its mathematical formulation in the celebrated `Strong Cosmic Censorship Conjecture' due to Roger Penrose. I will present my results on the linear analog of this conjecture in the case of negative cosmological constant. It turns out that this is intimately tied to Diophantine properties of a suitable ratio of mass and angular momentum of the black hole due to the presence of slowly decaying quasinormal modes on the black hole exterior. If time permits, I will further discuss a related result (joint with M. Van de Moortel) on Strong Cosmic Censorship for spherical symmetry dynamical black holes in the presence of slow decay.