Bekenstein’s proposal seemed to imply that there are really jillions of different ways that spacetime can arrange itself at the microscopic quantum level to make a macroscopic classical black hole. All we have to do is figure out what those ways are. Easier said than done, as it turns out; more than thirty-five years later, we still don’t have a firm grasp on the nature of those microstates implied by the black-hole entropy formula.
