For the classical wave equation the map from initial data to Friedlander?s radiation field is an isometry in energy spaces. I will explain the limitations of classical scattering theory, in the setting of slowly decaying initial data, or slowly decaying forcing terms, which entail the failure of Huygens principle. I will then describe my recent joint work with Hans Lindblad (Johns Hopkins) on the construction of scattering solutions in this context, and highlight the role of homogeneous functions in the interior and exterior of the light cone