= Gauge-gravity duality
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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.
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