Quantum gravity as sum over spacetimes

@article{Ambjorn2010QuantumGA,
  title={Quantum gravity as sum over spacetimes},
  author={Jan Ambjorn and Jerzy Jurkiewicz and R Loll},
  journal={Lecture Notes in Physics},
  year={2010},
  volume={807},
  pages={59-124}
}
A major unsolved problem in theoretical physics is to reconcile the classical theory of general relativity with quantum mechanics. These lectures will deal with an attempt to describe quantum gravity as a path integral over geometries. Such an approach has to be non-perturbative since gravity is a non-renormalizable quantum field theory when the dimension of spacetime is four. 
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