Lectures on Loop Quantum Gravity - [jnl article] T.Thiemann WW.pdf

arXiv:gr-qc/0210094 v1 28 Oct 2002
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******@aei-
mMulneg1 47 omna osa,Germany Potsdam, near Golm 14476 M¨uhlenberg 1, Am
P .Gaiainpyi,Albert-Einstein-Institut, Gravitationsphysik, f. MPI
etrso opQatmGravity Quantum Loop on Lectures
rpitAEI-2002-087 Preprint
.Thiemann T.
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Abstract
Quantum General Relativity (QGR), sometimes called Loop Quantum Gravity, has matured over
the past fifteen years to a mathematically rigorous candidate quantum field theory of the gravita-
tional field. The features that distinguish it from other quantum gravity theories are 1) background
independence and 2) minimality of structures.
Background independence means that this is a non-perturbative approach in which one does not
perturb around a given, distinguished, classical background metric, rather arbitrary fluctuations are
allowed, thus precisely encoding the quantum version of Einstein’s radical perception that gravity is
geometry.
Minimality here means that one explores the logical consequences of bringing together the two
fundamental principles of modern physics, namely general covariance and quantum theory, without
adding any experimentally unverified additional structures such as extra dimensions, extra symme-
tries or extra particle content beyond the standard model. While this is a very conservative approach
and thus maybe not very attractive to many researchers, it has the advantage that pushing the theory
to its logical frontiers will undoubtedly either result in a essful theory or derive exactly which
extra structures are required, if necessary. Or put even more radically, it may show which basic
principles of physics have to be given up and must be replaced by more fundamental ones.
QGR therefore is, by definition, not a unified theory of all interactions in the standard sense
since such a theory would require a new symmetry principle. However, it unifies all presently known
interactions in a new sense by quantum mechanically imple