author={Carlos Barcel{\'o} and Matt Visser},
  journal={International Journal of Modern Physics D},
The tension, if not outright inconsistency, between quantum physics and general relativity is one of the great problems facing physics at the turn of the millennium. Most often, the problems arising in merging Einstein gravity and quantum physics are viewed as Planck scale issues (1019GeV, 10-34m, 10-45s), and so safely beyond the reach of experiment. However, over the last few years it has become increasingly obvious that the difficulties are more widespread: There are already serious problems… 

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