

1 Introduction
At high enough energies, Einstein’s theory of general relativity
breaks down, and will be superceded by a quantum gravity theory.
The classical singularities predicted by general relativity in
gravitational collapse and in the hot big bang will be removed by
quantum gravity. But even below the fundamental energy scale that
marks the transition to quantum gravity, significant corrections to
general relativity will arise. These corrections could have a major
impact on the behaviour of gravitational collapse, black holes, and
the early universe, and they could leave a trace - a “smoking gun”
- in various observations and experiments. Thus it is important to
estimate these corrections and develop tests for detecting them or
ruling them out. In this way, quantum gravity can begin to be
subject to testing by astrophysical and cosmological observations.
Developing a quantum theory of gravity and a
unified theory of all the forces and particles of nature are the
two main goals of current work in fundamental physics. There is as
yet no generally accepted (pre-)quantum gravity theory. Two of the
main contenders are M theory (for recent reviews see, e.g.,
[153, 263, 283]) and quantum
geometry (loop quantum gravity; for recent reviews see, e.g., [272, 306]). It is important to
explore the astrophysical and cosmological predictions of both
these approaches. This review considers only models that arise
within the framework of M theory, and mainly the 5-dimensional
warped brane-worlds.

