At the singularity, the laws of physics break down, including Einstein's Theory of General Relativity. This is known as Quantum Gravity. In this realm, space and time are broken apart and cause and effect cannot be unraveled. Even today, there is no satisfactory theory for what happens at and beyond the rim of the singularity. A rotating black hole has an interesting feature, called a Cauchy horizon, contained in its interior. The Cauchy horizon is a light-like surface which is the boundary of the domain of validity of the Cauchy problem. What this means is that it is impossible to use the laws of physics to predict the structure of the region after the Cauchy horizon. This breakdown of predictability has led physicists to hypothesize that a singularity should form at the Cauchy horizon, forcing the evolution of the interior to stop at the Cauchy horizon, rendering the idea of a region after it meaningless. Recently this hypothesis was tested in a simple black hole model. A spherically symmetric black hole with a point electric charge has the same essential features as a rotating black hole. It was shown in the spherical model that the Cauchy horizon does develop a scalar curvature singularity. It was also found that the mass of the black hole measured near the Cauchy horizon diverges exponentially as the Cauchy horizon is approached. This led to this phenomena being dubbed "mass inflation." In order to understand what exactly a black hole is, we must first take a look at the basis for the cause of a black hole. All black holes are formed from the gravitational collapse of a star, usually having a great, massive, core. A star is created when huge, gigantic, gas clouds bind together due to attractive forces and form a hot core, combined from all the energy of the two gas clouds. This energy produced is so great when it first collides, that a nuclear reaction occurs and the gases within the star start to burn continuously.
