ENTROPY GENERATION BY TUNNELING IN 2+1 GRAVITY

The tunneling approach for entropy generation in quantum gravity is sh own to be valid when applied to three-dimensional (3D) general relativ ity. The entropy of de Sitter and Reissner-Nordstr6m external event ho rizons and of the 3D black hole obtained by Banados and co-workers is rederived from the tunneling of the metric to these spacetimes. The an alysis for spacetimes with an external horizon is carried out in compl ete analogy with the 4D case. However, we find significant differences for the black hole. It was previously shown that the tunneling approa ch implies a large, maybe infinite, degeneracy of the configuration th at tunnels to the four-dimensional black hole. For the three-dimension al black hole we find that the initial configuration may not yield suc h a highly degenerate object.