UCL in the News: Black holes may harbour their own universes

The theory that predicted black holes in the first place - general relativity - says that all the matter inside them gets squashed into a central point of infinite density called a singularity.

But then, "things break down mathematically", says Dr Christian Böhmer [UCL Mathematics]. "We would like to see the singularity removed." …

Böhmer and colleague Kevin Vandersloot of the University of Portsmouth in the UK use … loop quantum gravity, which defines space-time as a network of abstract links that connect tiny chunks of space. …

Böhmer and Vandersloot wanted to see what happened if they applied loop quantum gravity to black holes in general. Because loop quantum gravity equations cannot be solved exactly for the inside of every black hole, the researchers used computers to approximate what would happen to the infalling matter.

"We were very surprised about the results," Böhmer says. Instead of a boundary around the singularity, they got two other kinds of solutions - both bizarre - that replaced the singularity.

Böhmer realised that one set of answers looked like a so-called 'Nariai universe' - a mathematical model of a universe allowed by general relativity in which the universe expands in only one spatial direction. …

"The interior becomes a universe of its own," Böhmer says. Instead of matter falling into a singularity, it would travel forever through this Nariai universe, which it would experience as infinite in size - even though it fits inside a black hole of finite size.

The other set of solutions they came up with were for a tunnel-like connection between the mouths of two black holes. The tunnel is reminiscent of a wormhole, a hypothetical feature of space-time that connects two distance points via a shortcut. In this case, it's not clear yet what would happen to matter inside, but it could oscillate back and forth inside of the two-mouthed black hole. …

Mason Inman, NewScientist.com