  We discuss how the diffraction theory of a single translation bounded measure
or a family of such measures can be understood within the framework of unitary
group representations. This allows us to prove an orthogonality feature of
measures whose diffractions are mutually singular. We apply this to study
dynamical systems, the refined Eberlein decomposition and validity of a
Bombieri--Taylor type result in a rather general context. Along the way we also
use our approach to (re)prove various characterisations of pure point
diffraction.
