What “naked” singularities are revealing about quantum space-time

Deep inside a black hole, the cosmos gets twisted beyond comprehension. Here, at some infinitesimal point of infinite density, the fabric of the universe gets so ludicrously warped that Albert Einstein’s general theory of relativity, which describes how mass bends space-time, ceases to make sense. At the singularity, our understanding falls apart.

As daunting as singularities are, each one is at least safely tucked away inside the event horizon of a black hole, the boundary beyond which we can’t see. This not only cloaks them from view, but also stops unknown effects they herald, namely the horrors of unpredictability, from leaching out into the wider universe. But what if singularities could exist outside black holes after all?

That question, given fresh impetus in recent years by demonstrations that general relativity allows for this, has spurred theorists to probe singularities from a deeper perspective, folding in insights from the latest forays into the possible quantum foundations of gravity. Already, they are realising that this new approach “flips the script” on how we think about singularities, says Netta Engelhardt at the Massachusetts Institute of Technology.

Fair warning: the work takes us into some labyrinthine physics. But by grappling with singularities in this way, Engelhardt and her colleagues are deciphering the enigmatic connections between the quantum realm and classical gravity – and reinforcing the revolutionary idea that…