Recently, there has been much interest in a new kind of “unspeakable” quantum information
that stands to regular quantum information in the same way that a direction in space or a …

Abstract The Problem of Time occurs because the 'time'of GR and of ordinary Quantum
Theory are mutually incompatible notions. This is problematic in trying to replace these two …

The aim of this paper is to provide a general introduction to the problem of time in quantum
gravity. This problem originates in the fundamental conflict between the way the concept …

The problem of time in quantum gravity calls for a relational solution. Using quantum
reduction maps, we establish a previously unknown equivalence between three approaches …

The asymmetry of nature under a'reversal of time'(that is, a reversal of motion and change)
appears only too obvious to us, as it deeply affects our own form of existence. If physics is to …

All physical observations are made relative to a reference frame, which is a system in its own
right. If the system of interest admits a group symmetry, the reference frame observing it must …

The standard formulation of quantum theory relies on a fixed space-time metric determining
the localisation and causal order of events. In general relativity, the metric is influenced by …

A solution to the issue of time in quantum gravity is proposed. The hypothesis that time is not
defined at the fundamental level (at the Planck scale) is considered. A natural extension of …

We give a consistent quantum description of time, based on Page and Wootters's conditional
probabilities mechanism, which overcomes the criticisms that were raised against similar …

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