  We consider string theory in a time dependent orbifold with a null
singularity. The singularity separates a contracting universe from an expanding
universe, thus constituting a big crunch followed by a big bang. We quantize
the theory both in light-cone gauge and covariantly. We also compute some tree
and one loop amplitudes which exhibit interesting behavior near the
singularity. Our results are compatible with the possibility that strings can
pass through the singularity from the contracting to the expanding universe,
but they also indicate the need for further study of certain divergent
scattering amplitudes.
