  In a collision of strongly coupled quantum matter we find that the dynamics
of the collision produces regions where a local rest frame cannot be defined
because the energy-momentum tensor does not have a real time-like eigenvector.
This effect is purely quantum mechanical, since for classical systems, a local
rest frame can always be defined. We study the relation with the null and weak
energy condition, which are violated in even larger regions, and compare with
previously known examples. While no pathologies or instabilities arise, it is
interesting that regions without a rest frame are possibly present in heavy ion
collisions.
