# nLab cosmic censorship hypothesis

Contents

### Context

#### Gravity

gravity, supergravity

# Contents

## Idea

The (weak or strong) cosmic censorship hypothesis is a conjecture due Roger Penrose in the theory of Einstein-gravity (general relativity) saying that under physically reasonable conditions all singularities in spacetime have to be behind an event horizon.

The weak cosmic censorship conjecture has many counterexamples in dimension $d \geq 5$. In (Crisford-Santos 17) finally a counterexample in $d = 4$ was found. The counterexample involves large electromagnetic field contributions in Einstein-Maxwell theory.

Hence if the cosmic censorship hypothesis is to become true, it needs to add some assumption on the nature of the extra force fields besides gravity.

Cumrun Vafa has argued that the weak gravity conjecture will save the cosmic censorship conjecture. The weak gravity conjecture says that in consistent theories of quantum gravity the gravitational force exerted by any object (e.g. a black hole) has to be weaker, in suitable units, than any other force. As discussed in (Crisford-Santos 17) it seems plausible that this constraint would indeed rule out the counterexample constructed there:

Subsequent calculations by Santos and Crisford supported Vafa’s hunch; the simulations they’re running now could verify that naked singularities become cloaked in black holes right at the point where gravity becomes the weakest force. (Wolchover, June 20 2017)

The weak gravity conjecture was motivated from string theory, where there are various plausibility arguments that it holds.

## References

Survey:

A formalization and proof of one version of the hypothesis, and discussion of relation to computability in physics and Malament–Hogarth spacetimes is in

• Gabor Etesi, A proof of the Geroch-Horowitz-Penrose formulation of the strong cosmic censor conjecture motivated by computability theory (arXiv:1205.4550)

A counterexample in 4 dimensions was found in

• Toby Crisford, Jorge Santos, Violating weak cosmic censorship in AdS$_4$, Phys. Rev. Lett. 118, 181101 (2017) (arXiv:1702.05490)

More on this and the relation to the weak gravity conjecture: