Dimension and Dimensional Reduction in Quantum Gravity

Abstract

A number of very different approaches to quantum gravity contain a common thread, a hint that spacetime at very short distances becomes effectively two dimensional. I review this evidence, starting with a discussion of the physical meaning of "dimension" and concluding with some speculative ideas of what dimensional reduction might mean for physics.

33 page draft of solicited review article -- comments and added references welcome; v2: many added references, minor clean-up