Spacetime Singularities and Cosmic Censorship Conjecture: A Review with Some Thoughts

Abstract

The singularity theorems of Hawking and Penrose tell us that singularities are common place in general relativity. Singularities not only occur at the beginning of the Universe at the Big Bang, but also in complete gravitational collapses that result in the formation of black holes. If singularities - except the one at the Big Bang - ever become "naked", i.e., not shrouded by black hole horizons, then it is expected that problems would arise and render general relativity indeterministic. For this reason, Penrose proposed the cosmic censorship conjecture, which states that singularities should never be naked. Various counterexamples to the conjecture have since been discovered, but it is still not clear under which kind of physical processes one can expect violation of the conjecture. In this short review, I briefly examine some progresses in spacetime singularities and cosmic censorship conjecture. In particular, I shall discuss why we should still care about the conjecture, and whether we should be worried about some of the counterexamples. This is not meant to be a comprehensive review, but rather to give an introduction to the subject, which has recently seen an increase of interest.

References updated; Invited review to appear in International Journal of Modern Physics A

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• Black Bounces with multiple throats and anti-throats
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• Cosmic censorship, massless fermionic test fields, and absorption probabilities
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• Singularity Avoidance in Gravitational Collapse of an Inhomogeneous Fluid in Rastall Gravity
• Gravitational Collapse of an Inhomogeneous Fluid in Rastall Theory
• The no-hair theorems at work in the tidal disruption event AT2020afhd
• Gaussian Planck Relics are Ruled-Out as Dark Matter by LIGO