  Quantum field theory (QFT) on non-stationary spacetimes is well understood
from the side of the algebra of observables. The state space, however, is
largely unexplored, due to the non-existence of distinguished states (vacuum,
scattering states, thermal states). Project C7 of the SFB 676 was focused on
characterisations of states by asymptotic conditions, e.g. holography (in case
the boundary has sufficiently many symmetries), on a precise version of an
approximate particle interpretation (for instance in Robertson--Walker
spacetimes) and on the determination in terms of expectation values of locally
covariant fields. Additionally, the backreaction of quantum matter fields on
the curvature as well as the perturbative quantisation of the
Einstein--Klein--Gordon system in the case of a cosmological background have
been investigated. Finally, a detailed analysis and construction of equilibrium
states for interacting field theories has been performed.
