Abstract:聽In condensed matter physics, plasma physics, and nuclear and particle physics, it is often taken for granted that while systems can be out of equilibrium, a local rest frame for matter can always be defined. After all, this seemingly innocuous assumption just states that, at least locally, there should be a frame with respect to which matter is not moving. In this talk, I will give examples of systems in flat space where a local rest frame can not be defined. I will link this observation to energy conditions in GR and speculate about possible consequences.
