Singularity

A singularity is a point or region where general relativity predicts infinite spacetime curvature and infinite density. It appears at the center of a black hole and at the origin of the Big Bang.

The Penrose-Hawking singularity theorems (1960s-1970s) proved that singularities are not artifacts of special symmetry assumptions but are generic predictions of general relativity under physically reasonable conditions. If enough mass is concentrated in a small enough region, gravitational collapse to a singularity is inevitable.

However, a singularity is almost universally understood not as a physical reality but as a signal that the theory breaks down. General relativity is a classical theory – it does not incorporate quantum mechanics. At the extreme densities and curvatures near a singularity, quantum gravitational effects should become dominant. Since no complete theory of quantum gravity exists, we cannot say what actually happens at the center of a black hole or at the very beginning of the universe.

The singularity is hidden behind the event horizon and therefore cannot be directly observed by an outside observer. The “cosmic censorship conjecture” (Penrose, 1969) proposes that all singularities produced by gravitational collapse are hidden behind horizons – that nature does not permit “naked” singularities visible to the outside universe. This conjecture remains unproven.