According to the ’t Hooft–Susskind holography, the black hole entropy, SBH, is
carried by the chaotic microscopic degrees of freedom, which live in the near horizon region
and have a Hilbert space of states of finite dimension d=exp(SBH). In previous work we
have proposed that the near horizon geometry, when the microscopic degrees of freedom can
be resolved, can be described by the AdS2[ZN] discrete, finite and random geometry, where
N∝SBH. What had remained as an open problem is how the smooth
AdS2 geometry can be recovered, in the limit when N→∞. In this contribution, we present the salient points of the solution to
this problem, which involves embedding the discrete and finite AdS2[ZN] geometry
in a family of finite geometries, AdSM2[ZN], where M is another integer. This family can be
constructed by an appropriate toroidal compactification and discretization of the ambient
(2+1)-dimensional Minkowski space-time. In this construction N and M can be understood
as “infrared” and “ultraviolet” cutoffs respectively. This construction allows us to
obtain the continuum limit of the AdSM2[ZN] discrete and finite geometry, by taking both N
and M to infinity in a specific correlated way, following a reverse process: Firstly, by recovering the continuous, toroidally compactified, AdS2[ZN] geometry, by removing the ultraviolet cutoff; secondly, by removing the infrared
cutoff, in a specific decompactification limit, while keeping the radius of AdS2 finite. It is
in this way that we recover the standard non-compact AdS2 continuum space-time. This
method can be applied directly to higher-dimensional AdS spacetimes.
