In three spacetime dimensions, general relativity drastically simplifies, becoming a "topological" theory with no propagating local degrees of freedom. Nevertheless, many of the difficult conceptual problems of quantizing gravity are still present. In this review, I summarize the rather large body of work that has gone towards quantizing (2 + 1)-dimensional vacuum gravity in the setting of a spatially closed universe.

中文翻译：

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2 + 1 维中的量子引力：封闭宇宙的情况。


在三个时空维度中，广义相对论大大简化，成为一种没有传播局部自由度的“拓扑”理论。尽管如此，量子引力的许多困难概念问题仍然存在。在这篇评论中，我总结了在空间封闭宇宙的背景下量化 (2 + 1) 维真空引力的相当大量的工作。