Absence of a local rest frame in far from equilibrium quantum matter

Understand

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.