Blackbody radiation is the radiation given off an object solely as a result of its absolute temperature. The (continuous) spectrum is given solely by the temperature.
How can this be? Why should a slab of Tungsten at 400 K emit the exact same spectrum as a pile of powdered sodium chloride at the same temperature? Why should the emitted radiation be independent of the chemical composition of the object, the electron transition energies, and the mass of the atomic nuclei?
What is the actual, physical process, that gives rise to the emission of blackbody radiation?