The holographic principle
Abstract
There is strong evidence that the area of any surface limits the information content of adjacent spacetime regions, at 1.4×10^{69} bits per square meter. This article reviews the developments that have led to the recognition of this entropy bound, placing special emphasis on the quantum properties of black holes. The construction of light sheets, which associate relevant spacetime regions to any given surface, is discussed in detail. This article explains how the bound is tested, and its validity is demonstrated in a wide range of examples. A universal relation between geometry and information is thus uncovered. It has yet to be explained. The holographic principle asserts that its origin must lie in the number of fundamental degrees of freedom involved in a unified description of spacetime and matter. It must be manifest in an underlying quantum theory of gravity. This article surveys some successes and challenges in implementing the holographic principle.
 Publication:

Reviews of Modern Physics
 Pub Date:
 August 2002
 DOI:
 10.1103/RevModPhys.74.825
 arXiv:
 arXiv:hepth/0203101
 Bibcode:
 2002RvMP...74..825B
 Keywords:

 04.70.Dy;
 04.60.m;
 02.40.Xx;
 97.60.Lf;
 Quantum aspects of black holes evaporation thermodynamics;
 Quantum gravity;
 Singularity theory;
 Black holes;
 High Energy Physics  Theory;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology;
 Quantum Physics
 EPrint:
 52 pages, 10 figures, invited review for Rev. Mod. Phys