  Exceptional points in an optical dimer of spheres, which have the same size
and operate in the spectral region of the dipolar resonance, are considered. By
choosing different materials of these spheres, we can offset the radiative loss
and create a gain-loss contrast to achieve a parity-time (PT)-symmetric dimer.
In this case, an exceptional point corresponds to the point where the PT
symmetry is broken. At the same time, if we consider a symmetric dimer, where
both spheres are made of the same material (which may have a purely real
dielectric constant), exceptional points occurring due to the radiative loss
non-Hermiticity can also be observed.
  We study the transition between the two regimes and demonstrate that the
exceptional point emerges due to the retardative nature of the coupling between
the spheres, which makes the equation for eigenfrequencies nonlinear and allows
it to have nontrivial solutions even when there is no contrast between the
spheres.
