The holographic principle

TL;DR

The paper reviews the holographic principle, highlighting how surface area limits information content in spacetime, discusses its quantum and black hole implications, and explores its role in quantum gravity theories.

Contribution

It provides a comprehensive review of the development, testing, and challenges of the holographic principle, emphasizing the connection between geometry and information.

Findings

Entropy bounds are supported by black hole physics.

Light-sheet construction tests validate the entropy limit.

The holographic principle suggests a fundamental link between geometry and quantum information.

Abstract

There is strong evidence that the area of any surface limits the information content of adjacent spacetime regions, at 10^(69) bits per square meter. We review 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. We explain how the bound is tested and demonstrate its validity 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. We survey some successes and challenges in implementing the holographic principle.