Spacetime singularities and cosmic censorship

6 problems

• Are generic spacelike singularities locally oscillatory, as the BKL picture predicts?

  Open

  Near the Big Bang or deep inside a black hole, each small region of space is predicted to stretch and squeeze chaotically in an endless sequence, a picture due to the Soviet physicists Belinskii, Khalatnikov and Lifshitz (BKL). This has never been proved for general solutions.

• Prove generic naked singularity formation from five-dimensional black string instability

  Open

  In five spacetime dimensions a long thin black hole shaped like a string breaks into a chain of smaller black holes, much as a stream of water breaks into drops. Simulations show the pinch-off exposes a singularity to distant observers without fine tuning, but there is no proof.

• Is the generic Kerr Cauchy horizon a weak null singularity?

  Partially resolved

  Inside a spinning black hole, disturbances pile up at an inner surface called the Cauchy horizon. The spacetime is known to stay continuous there, but it is not proved that it becomes too rough for Einstein's equations to continue beyond it.

• What replaces the Schwarzschild singularity in quantum gravity?

  Open

  General relativity predicts that everything inside a black hole ends at a singularity after a finite time. A quantum theory of gravity should replace this with something finite, but no calculation shows what.

• Does strong cosmic censorship hold for charged black holes in de Sitter space?

  Contested

  Strong cosmic censorship says that the future inside a black hole cannot be continued predictably past a surface called the Cauchy horizon. For charged black holes in a universe with a positive cosmological constant, classical calculations suggest it can fail, and quantum effects may restore it.

• Prove weak cosmic censorship for generic 4D vacuum gravitational collapse

  Open

  Weak cosmic censorship says that collapsing matter or gravitational waves never produce a singularity visible from far away, except in finely tuned cases. It has been proved only under strong symmetry assumptions.