  We investigate features of perturbative gravity and supergravity by studying
scattering in the ultraplanckian limit, and sharpen arguments that the dynamics
is governed by long-distance physics. A simple example capturing aspects of the
eikonal resummation suggests why short distance phenomena and in particular
divergences or nonrenormalizability do not necessarily play a central role in
this regime. A more profound problem is apparently unitarity. These
considerations can be illustrated by showing that known gravity and
supergravity amplitudes have the same long-distance behavior, despite the extra
light states of supergravity, and this serves as an important check on
long-range dynamics in a context where perturbative amplitudes are finite. We
also argue that these considerations have other important implications: they
obstruct probing the conjectured phenomenon of asymptotic safety through a
physical scattering process, and ultraplanckian scattering exhibiting Regge
behavior. These arguments sharpen the need to find a nonperturbative completion
of gravity with mechanisms which restore unitarity in the strong gravity
regime.
