Alasdair Routh (left) is a Ph.D. student in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge. Wout Merbis (right) is a Ph.D. student at the Centre for Theoretical Physics of the University of Groningen.

Einstein’s gravitational field equations, which relate the geometry of spacetime to the matter in it, can also be applied to a spacetime of three dimensions (3D) but in this case the matter completely determines the geometry, so there is no “room” for gravitational waves: gravitons in the quantum theory. However, in 3D there is a simple extension of Einstein’s second-order equations to the third-order equations of “Topologically-Massive Gravity” (TMG), which propagates a single massive spin-2 mode; i.e. a massive graviton.

In the context of asymptotically anti-de Sitter (AdS) space times, both 3D Einstein gravity and TMG are potentially semi-classical approximations to some consistent 3D quantum gravity theory defined, via the AdS/CFT correspondence, in terms of a 2D conformal field theory (CFT). However, Continue reading →