General relativity in (1 + 1) dimensions

We describe a theory of gravity in (1 + 1) dimensions that can be thought of as a toy model of general relativity. The theory should be a useful pedagogical tool, because it is mathematically much simpler than general relativity but shares much of the same conceptual structure; in particular, it gives a simple illustration of how gravity arises from spacetime curvature. We derive the theory from fundamental physical principles using two different methods, one based on extrapolating from Newtonian gravity and one based on the equivalence principle, and present several exact solutions.