Revisit Cosmic Censorship and Black Holes

General relativity is the most successful theory of gravity and is one of the paradigms of current physics and astrophysics. However, since it cannot describe gravitational interactions between objects whose motions are described by quantum theory, nobody would disagree with the assertion that a new theory beyond general relativity is needed. General relativity predicts that black holes form through gravitational collapses of massive objects and spacetime singularities appear in them. The black hole is regarded as a key of the theory beyond general relativity through the information-loss problem. Furthermore, the prediction of spacetime singularity formation is regarded as a flaw of general relativity, and it is frequently asserted that this fact gives us another motivation for looking for the new theory, besides the gravitational interactions between quantum objects. Then there are two messages in this chapter, which are not necessarily novel but have rarely been pointed out. One is that the spacetime singularity cannot be necessarily a motivation for the new theory. The cosmic censorship hypothesis gives us an important perspective on this issue. The other is that if the new theory beyond general relativity is established in the quantum framework, it seems to be impossible that the corresponding concept to the black hole in general relativity exists in the new theory.