Cosmic censorship conjecture (R. Penrose, 1979)
The conjecture, so far completely undemonstrated in the context of general relativity, that all singularities (along the possible exception of the big bang singularity) are accompanied through event horizons which totally surround them at all points in time. i.e., problematic issues along with the singularity are rendered irrelevant, as no information can ever escape from a black hole's event horizon.