  The standard theory of ideal gases ignores the interaction of the gas
particles with the thermal radiation (photon gas) that fills the otherwise
vacuum space between them. This is an unphysical feature of the theory since
every material in this universe, and hence also the particles of a gas, absorbs
and radiates thermal energy. The interaction with the thermal radiation that is
contained within the volume of the body may be important in gases since the
latter, unlike solids and liquids, are capable of undergoing conspicuous volume
changes. Taking this interaction into account makes the behaviour of the ideal
gases more realistic and removes Gibbs' paradox.
