How does the entropy/information bound work?

Abstract

According to the universal entropy bound, the entropy (and hence information capacity) of a complete weakly self-gravitating physical system can be bounded exclusively in terms of its circumscribing radius and total gravitating energy. The bound's correctness is supported by explicit statistical calculations of entropy, gedanken experiments involving the generalized second law, and Bousso's covariant holographic bound. On the other hand, it is not always obvious in a particular example how the system avoids having too many states for given energy, and hence violating the bound. We analyze in detail several purported counterexamples of this type, and exhibit in each case the mechanism behind the bound's efficacy. © 2005 Springer Science+Business Media, Inc.