AdS/CFT correspondence (Maldacena 1997) equates a gravitational theory in (d+1)-dimensional anti-de Sitter space
to a conformal field theory on the d-dimensional boundary. The bulk-to-boundary propagator
K(z,x;x') = (z/(z²+|x-x'|²))^Δ encodes how boundary sources excite bulk fields.
The Ryu-Takayanagi formula (2006) identifies the entanglement entropy of a boundary region A
with the area of the minimal bulk geodesic (in 2+1D: length) homologous to A:
S(A) = Area(γ_A)/(4G_N). This visualizes the Poincaré patch of AdS₂ with the boundary at z→0,
showing bulk-to-boundary propagators and RT geodesics as semicircles.