In statistical mechanics entropy is a measure of disorder obeying Boltzmann's formula $S=\log{ \cal N}$, where ${ \cal N}$ is the accessible phase space volume. In black hole thermodynamics one associates to a black hole an entropy Bekenstein-Hawking $S_{ BH}$. It is well known that $S_{ BH}$ is very large for astrophysical black holes, much larger than any collection of material objects that could have given rise to the black hole. If $S_{ BH}$ is an entropy the question is thus what is the corresponding ${ \cal N}$, and how come this very large phase space volume is only opened up to the universe by a gravitational collapse, which from another perspective looks like a massive loss of possibilities. I advance a hypothesis that the very large increase in entropy can perhaps be understood as an effect of classical gravity, which eventually bottoms out when quantum gravity comes into play. I compare and discuss a selection of the very rich literature around these questions.
Categories: gr-qc quant-ph