Holographic Principle and String Cosmology

TL;DR

This paper explores how the holographic principle constrains string cosmology, showing that a graceful exit mechanism is necessary for a nonsingular universe and analyzing conditions for flat and open universes to satisfy holographic bounds.

Contribution

It demonstrates the necessity of a graceful exit for holography in string cosmology and clarifies conditions under which flat and open universes comply with holographic bounds.

Findings

Flat universe requires an initial cold, vacuum state for holography.

Particle entropy saturates the holographic bound during the graceful exit.

Open universe always satisfies holography regardless of initial conditions.

Abstract

String cosmology is revisited from cosmological viewpoint of holographic principle put forward by `t Hooft, and by Fischler and Susskind. It is shown that the holography requires existence of a `graceful exit' mechanism, which renders the Universe nonsingular by connecting pre- and post-big bang phases smoothly. It is proven that flat Universe is consistent with the holography only if it starts with an absolutely cold and vacuous state. Particle entropy produced during the `graceful exit' apparently saturates the holography bound. Open Universe can always satisfy the holography no matter what initial state of the Universe is.