  Canonical methods can be used to construct effective actions from deformed
covariance algebras, as implied by quantum-geometry corrections of loop quantum
gravity. To this end, classical constructions are extended systematically to
effective constraints of canonical quantum gravity and applied to model systems
as well as general metrics, with the following conclusions: (i) Dispersion
relations of matter and gravitational waves are deformed in related ways,
ensuring a consistent realization of causality. (ii) Inverse-triad corrections
modify the classical action in a way clearly distinguishable from curvature
effects. In particular, these corrections can be significantly larger than
often expected for standard quantum-gravity phenomena. (iii) Finally, holonomy
corrections in high-curvature regimes do not signal the evolution from collapse
to expansion in a "bounce," but rather the emergence of the universe from
Euclidean space at high density. This new version of signature-change cosmology
suggests a natural way of posing initial conditions, and a solution to the
entropy problem.

General Relativity and Quantum Cosmology;Cosmology and Nongalactic Astrophysics;High Energy Physics - Theory