Topic: quantum states

Representing quantum states through measurement probabilities can preserve subsystem structure or faithfully track nearby states, but not necessarily both. This creates robustness problems for axiomatic reconstructions based on generalized probabilistic theories. The talk introduces an operational alternative that treats a state as an observer's knowledge, aiming to compare possible physical theories while avoiding instability under small changes of the theory.

This proposal treats constraint-violating quantum states as stages of time and evolution as gradual collapse toward diffeomorphism invariance. Random lapse and shift fluctuations drive the process, while a monotonically increasing scale factor supplies a clock. Scalar, vector and tensor gravitational modes initially appear; at long times the extra modes are damped and tensor modes approach unitary evolution. The talk considers possible physical consequences of the transient additional excitations.