  We study massless open and closed string scattering amplitudes in flat space
at high energies. Similarly to the case of AdS space, we demonstrate that,
under the T-duality map, the open string amplitudes are given by the
exponential of minus minimal surface areas whose boundaries are cusped closed
loops formed by lightlike momentum vectors. We show further that the closed
string amplitudes are obtained by gluing two copies of minimal surfaces along
their cusped lightlike boundaries. This can be thought of as a manifestation of
the Kawai-Lewellen-Tye (KLT) relation at high energies. We also discuss the KLT
relation in AdS/CFT and its possible connection to amplitudes in N=8
supergravity as well as the correlator/amplitude duality.
