  Two non--interacting quantum systems which couple to a common environment
with many degrees of freedom initially in thermal equilibrium can become
entangled due to the indirect interaction mediated through this heat bath. I
examine here the dynamics of reservoir induced entanglement for a heat bath
consisting of a thermal electro--magnetic radiation field, such as black body
radiation or the cosmic microwave background, and show how the effect can be
understood as result of an effective induced interaction.
