Treating reference frames fundamentally as quantum systems is inevitable in quantum
gravity and also in quantum foundations once considering laboratories as physical systems …

Canonically,'classic'tests of general relativity (GR) include perihelion precession, the
bending of light around stars, and gravitational redshift;'modern'tests have to do with, inter …

In general relativity, the description of spacetime relies on idealised rods and clocks, which
identify a reference frame. In any concrete scenario, reference frames are associated to …

In this short review paper, relative evolution in time and related issues are analyzed within
classical and quantum mechanics. We first discuss the basics of quantum frames of …

Given the importance of quantum reference frames (QRFs) to both quantum and
gravitational physics, it is pertinent to develop a systematic method for switching between …

Local gauge theories are in a complicated relationship with boundaries. Whereas fixing the
gauge can often shave off unwanted redundancies, the coupling of different bounded …

What is time? The Janus Point offers a ground-breaking solution to one of the greatest
mysteries in physics. For over a century, the greatest minds have sought to understand why …

A bstract When a system emits gravitational radiation, the Bondi mass decreases. If the
Bondi energy is Hamiltonian, it can thus only be a time-dependent Hamiltonian. In this …

A “duality” is a formal mapping between the spaces of solutions of two empirically equivalent
theories. In recent times, dualities have been found to be pervasive in string theory and …

General relativity is usually formulated as a theory with gauge invariance under the
diffeomorphism group, but there is a'dilaton'formulation where it is in addition invariant under …