Loop quantum gravity: an outside view

  title={Loop quantum gravity: an outside view},
  author={Hermann Nicolai and Kasper Peeters and Marija Zamaklar},
  journal={Classical and Quantum Gravity},
  pages={R193 - R247}
We review aspects of loop quantum gravity in a pedagogical manner, with the aim of enabling a precise but critical assessment of its achievements so far. We emphasize that the off-shell (‘strong’) closure of the constraint algebra is a crucial test of quantum spacetime covariance, and thereby of the consistency, of the theory. Special attention is paid to the appearance of a large number of ambiguities, in particular in the formulation of the Hamiltonian constraint. Developing suitable… 

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