  Quantum field theory (QFT) in classical spacetime has revealed interesting
and puzzling aspects about gravitational systems, in particular black hole
thermodynamics and its information processing. Although quantum gravitational
effects may be relevant for a better understanding of these topics, a commonly
accepted framework for studying QFT with quantum gravitational effects is
missing. We present a theory for studying quantum fields in the presence of
quantum indefinite causal structure. This theory incorporates quantum
properties of spacetime causal structure in a model independent way, and
exposes universal features of quantum spacetime which are independent of the
details about its microscopic degrees of freedom (strings, loops, causal
sets...).
