  We prove a dichotomy regarding the behavior of one-parameter unipotent flows
on quotients of semisimple lie groups under time change. We show that if
$u^{(1)}_t$ acting on $G_{1}/\Gamma_1$ is such a flow it satisfies exactly one
of the following:
  (1) The flow is loosely Kronecker, and hence isomorphic after an appropriate
time change to any other loosely Kronecker system.
  (2) The flow exhibits the following rigid behavior: if the one-parameter
unipotent flow $u^{(1)} _ t$ on $G_1/\Gamma_1$ is isomorphic after time change
to another such flow $u^{(2)} _ t$ on $G_2/\Gamma _ 2$, then $G_1/\Gamma_1 $ is
isomorphic to $G_2/ \Gamma_2$ with the isomorphism taking $u^{(1)} _ t$ to
$u^{(2)} _ t$ and moreover the time change is cohomologous to a trivial one.
  The full details will appear in [LW23].
