15:16 31 October 2007/ NewScientist.com news service/ by Mason Inman
When matter gets swallowed by a black hole, it could fall into
another universe contained inside the black hole, or get trapped inside
a wormhole-like connection to a second black hole, a new study suggests.
What's
inside a black hole is one of the biggest mysteries in physics. 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 Christian Böhmer of University
College London, in the UK. "We would like to see the singularity
removed."
Many
researchers believe that some kind of new, overarching theory that
unites gravity and quantum effects will resolve the problem. String theory is the most popular of these alternatives.
But Böhmer and colleague Kevin Vandersloot of the University of Portsmouth in the UK use a rival approach called loop quantum gravity, which defines space-time as a network of abstract links that connect tiny chunks of space.
Loop
quantum gravity has been used before to tackle the singularity that
would seem to have occurred at the origin of our universe. It suggests
that instead of a big bang, an earlier universe could have collapsed
and then exploded outward again in a "big bounce".
Bizarre solutions
A
similar repulsiveness appeared when the loop quantum approach was
previously applied to the inside of a black hole with particular
properties. Those studies suggested there was a repulsive boundary that
blocked matter from clumping together in the singularity.
But
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.
(Our observed universe appears to be a "de Sitter space" instead
because it expands in all three dimensions, so that distant galaxies
move away from us no matter where we look in the sky.)
Infinite universe
"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.
The new study is a "significant step forward," says Carlo Rovelli of the Centre for Theoretical Physics in Marseille, France.
Inherently unstable
"The
idea of applying loop quantum gravity to resolve the singularity at the
centre of a black hole was started some time ago," he told New Scientist.
"But it is now reaching a stage of maturity, where one can indeed
compute concretely how quantum space-time in the centre of a black hole
could actually look."
But one physicist contacted by New Scientist
who did not want to be quoted by name says the new work may not
actually do away with the problem of singularities in black holes. He
says a Nariai universe is inherently unstable, so it would eventually
either collapse or become a de Sitter universe – which would itself
harbour black holes.
If
that is so, then black holes may contain their own universes, but those
universes would likely contain their own black holes, which could
contain their own universes … in an infinite loop.
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