  Here we discuss blackbody radiation within the context of classical theory.
We note that nonrelativistic classical mechanics and relativistic classical
electrodynamics have contrasting scaling symmetries which influence the
scattering of radiation. Also, nonrelativistic mechanical systems can be
accurately combined with relativistic electromagnetic radiation only provided
the nonrelativistic mechanical systems are the low-velocity limits of fully
relativistic systems. Application of the no-interaction theorem for
relativistic systems limits the scattering mechanical systems for thermal
radiation to relativistic classical electrodynamic systems, which involve the
Coulomb potential. Whereas the naive use of nonrelativistic scatterers or
nonrelativistic classical statistical mechanics leads to the Rayleigh-Jeans
spectrum, the use of fully relativistic scatterers leads to the Planck spectrum
for blackbody radiation within classical physics.
