 Gauge-gravity duality

Gauge-gravity duality relates a quantum field theory description to a description involving dynamical gravity, usually with additional string degrees of freedom. In the best-understood AdS/CFT correspondence, the field theory lives on the spacetime boundary and the gravitational description has an extra radial direction, possibly together with compact internal dimensions.

The two descriptions assign different variables to the same observables: a field-theory local field operator corresponds to a bulk field, and a boundary correlation function can be computed from a bulk response. A weakly curved classical bulk may describe strongly coupled field-theory dynamics when the required large-rank and coupling limits hold. The utility is therefore calculational as well as conceptual, but the existence of a field theory does not automatically guarantee a simple classical gravitational dual.