WHAT CAVITIES - CONTAINERS IN BLACK-HOLE THERMODYNAMICS

Most spherical thin shells, enclosing black-body radiation satisfy the dominant energy condition if their matter-energy is at least similar or equal to 30% of the total mass-energy. Containers with less matter-energy may be able to sustain high radiation pressures, but the radiation will be mostly unstable. Containers with negligible energy are either unable to sustain the radiation pressure or the radiation is unstable to gravitational collapse (or both at the same time). Containers with black holes and radiation in thermal equilibrium, considered in the literature, are often unrealistic.