It is possible to couple quantum and classical variables consistently (i.e. without paradoxes like faster than light signalling) provided one accepts a certain amount of stochasticity. This is useful, for example, if one wants to entertain the possibility that spacetime is fundamentally classical. These hybrid dynamics are not trivial (like meanfield) but they are nothing fancy either, and one...
An ordinary change between two classical reference frames (RF) A, B can be seen as a point $g$ in a Lie group manifold $G$; $g$ sharply specifies the orientation and motion (of the origin) of B relative to A, while the group product encodes the composition of two changes into a third one. So far, physical theories are characterized by their covariance under a suitable $G$. If A, B are...
Currently envisaged tests for probing the quantum nature of the gravitational interaction in the low-energy regime typically focus either on the quantized center-of-mass degrees of freedom of two spherically-symmetric test masses or on the rotational degrees of freedom of non-symmetric masses under a gravitational interaction in the Newtonian limit. In this talk, I am going to present a novel...
Starting from operationally motivated principles, we derive a relational theory of observables in Minkowski spacetime from which the notion of scalar quantum fields naturally emerges. We expand on quantum reference frames in spacetime and demonstrate that most properties of quantum fields arise as direct consequences of constraints on quantum reference frames -- that is, quantum fields should...
