Quantum Field Theory in Curved Spacetime (2nd Edition)

The 2023 second edition of a 2006 encyclopedia article on mathematical aspects of quantum field theory in curved spacetimes (QFTCST). Section-titles (with new sections indicated with stars) are: Introduction and preliminaries, Construction of a $*$-algebra for a real linear scalar field on globally hyperbolic spacetimes and some general theorems, *More about (quasifree) Hadamard states, Particle creation and the limitations of the particle concept, Theory of the stress-energy tensor, *More about the intersection of QFTCST with AQFT and the Fewster-Verch No-Go Theorem, Hawking and Unruh effects, *More about (classical and) quantum fields on black hole backgrounds, Non-globally hyperbolic spacetimes and the time-machine question, *More about QFT on non-globally hyperbolic spacetimes, Other related topics and some warnings. The article contains many references. It also includes a review of, and also compares and contrasts, recent results on the implications of QFTCST for the question of the instability of three sorts of Cauchy horizon -- first those inside black holes such as especially Reissner-Nordstr\"om-de Sitter and Kerr-de Sitter, second the compactly generated Cauchy horizons of spacetimes in which time-machines get manufactured, and third the Cauchy horizon of the spacetime which is believed to describe evaporating black holes and which underlies (one version of) the black hole information-loss puzzle.