Simple Summary We briefly review the problem of time in quantum cosmology and present
two possible solutions. Abstract Time in quantum gravity is not a well-defined notion despite …

Every clock is a physical system and thereby ultimately quantum. A naturally arising
question is thus how to describe time evolution relative to quantum clocks and, specifically …

Despite its importance in general relativity, a quantum notion of general covariance has not
yet been established in quantum gravity and cosmology, where, given the a priori absence …

We present a 3+ 1 formulation of the effective field theory framework called the standard
model extension in the gravitational sector. The explicit local Lorentz and diffeomorphism …

The local conservation of a physical quantity whose distribution changes with time is
mathematically described by the continuity equation. The corresponding time parameter …

We discuss the question of time in a Bianchi I quantum cosmology in the framework of
singularity avoidance. We show that time parameters fall into two distinct classes, that are …

We present the quantum model of the asymptotic dynamics underlying the Belinski–
Khalatnikov–Lifshitz (BKL) scenario. The symmetry of the physical phase space enables …

A quantum cosmological bouncing model may exhibit an ambiguity stemming from the
nonclassical nature of the background evolution: Two classically equivalent theories can …

Simple Summary We clarify the question of clock transformations and trajectories in
quantum cosmology in a vacuum Bianchi I minisuperspace. Abstract We consider a simple …

We present a generally covariant approach to quantum mechanics in which generalized
positions, momenta and time variables are treated as coordinates on a fundamental “phase …