AdS/CFT duality exactness
Prove the exact equivalence between string theory with gravity on anti–de Sitter space and a conformal field theory defined on its boundary (the AdS/CFT duality), thereby establishing the conjectured non-perturbative holographic correspondence.
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Additionally, there are attempts to construct a non-perturbative version of string theory; the most celebrated development being the AdS/CFT duality (also known as the Maldacena conjecture, after Maldacena 1998). This is a relationship—a conjectured exact equivalence—between a string theory featuring gravity, describing closed strings propagating on a spacetime (anti-de Sitter space (AdS)), known as the ‘bulk’, and a gauge theory without gravity (a conformal field theory (CFT)), defined on the boundary that contains the bulk spacetime.