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EINBLICKE
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Stars rotate. This angular momentum is a physical conserved
quantity, a constant. This means that black holes should also
be able to rotate. But according to the Schwarzschild solution
this is theoretically inconceivable. It was not until 1963 that
the New Zealander mathematician Roy Kerr came up with a
solution to Einstein's equations for rotating black holes. This
solution potentially describes all astrophysical black holes in
the universe. In addition to the event horizon they also have
other astounding properties. One of these is the so-called
static limit. This forms a boundary layer around the black hole.
Within this boundary everything – light, particles and even
spacecraft – even if endowedwith an arbitrarily large strength
of propulsion – is forced to move in the same direction in
which the black hole is rotating.
At the centre of a black hole – according to both the Schwarz-
schild solution and the Kerr metric – the gravitational potential
is infinitely large. This gives rise to a so-called space-time
curvature singularity. To avoid such singularities and bring
gravity in line with the theory of quantum mechanics, one
must move beyond Einstein's theory of general relativity and
construe a new theory: a theory of quantum gravity. Several
candidates for such a theory exist today. Among the most
promising is string theory, which requires more than three
spatial dimensions for its mathematical consistency.
This is where the “Models of Gravity” Research Training Group
comes in, whichwas launched in spring2012. This joint research
programme of the universities of Oldenburg and Bremen,
which is funded by the German Research Foundation (DFG)
and inwhich the uni-
versities of Bielefeld,
Hanover andCopen-
hagen (Denmark) are
also involved, aims
to reach a deeper understanding of gravitational phenomena
within the context of such extended theories of gravity. Exa-
mining the consequences of these theories for the properties
of black holes is a central concern of the training group. To this
end we are constructing new forms of space-time as solutions
to the extended equations. We are also studying the move-
ment of particles and light within these space-times since this
is the only way to understand the space-time continuum and
compare it with astrophysical observations. The Oldenburg
research group recently demonstrated that when adjusted to
string theory, black holes exhibit greater angular momentum
than black holes based on the Kerr solution. Moreover it was
able to prove that the time it takes to orbit such a black hole
candiffer considerably fromthe time it takes toorbit a Kerr hole.
But the research training group is not only interested in
astronomical black holes. High-energy collisions in the LHC
particle accelerator at the European research centre CERNwill
potentially be able to create microscopic black holes in the
future that will provide insights into the existence of further
spatial dimensions. If the detectors there were to record the
characteristic traces of black holes, it would fundamentally
alter our world view. The higher dimensions offer a broad
spectrum of new possibilities for black holes: event horizons
can be ring-shaped rather than just round. These, in turn, can
form spirals that result inmany new types of black hole, which
our research group is investigating.
Another focal point of our research is AdS /CFT correspondence
(
Anti-de-Sitter space / conformal field theory correspondence).
The term stands for the equivalence of two theories: one is
a gravitational theory for n-dimensional space; the other is a
field theory for the boundary of this space and thus of a lower
dimension. This correspondence offers a unique opportunity
to study physical systems for which approximate (perturbative)
calculations are not possible. In the physics of condensed
matter there are a variety of such systems which are also in-
teresting from a technological standpoint, whose properties
we can begin to study and learn about by constructing “dual”
black hole space-times.
The study of AdS /CFT correspondence provides insights into
the flowof thermal and electrical currents through a quantum
fluid of electrons. Such quantum fluids are found above the
phase transition to superconductivity when electrons move
into a quantum-critical state. Charged black holes can also
shed light on a number of previously unexplained properties
of high-temperature superconductors. Our research aims to
make it easier to understand hitherto inexplicable phenomena
of physical systems and the implications for energy transport.
This means that investigation of black holes can generate
knowledge that can also be relevant to our everyday lives.
The string theory requires more
than three spatial dimensions for
its mathematical consistency.
Es gibt kein Entrinnen: Nichts kann den Ereignishorizont verlassen.
The point of no return: nothing can escape the event horizon.
