Welcome and Opening Remarks

Alexander Smith Dartmouth College

Flaminia Giacomini Perimeter Institute for Theoretical Physics
Composite quantum particles as ideal quantum clocks — operational approach to quantum aspects of time
Magdalena Zych
University of Queensland (UQ)
In general relativity time requires an operational description, for example, associated with the reading of an idealised clock following some world line. I will show that in quantum physics idealised clocks can be modelled as composite quantum particles and discuss what foundational insights into the notion of time is enabled by this approach.
KappaMinkowski: physics with noncommutative time
Flavio Mercati
University of Naples Federico II
The kappaMinkowski noncommutative spacetime has been studied for a long time as an example of quantum spacetime with nontrivial commutation relations between spatial and temporal coordinates which, at first sight, seem to break Poincaré invariance. However kappaMinkowski is invariant under a Hopfalgebra deformation of the Poincaré group, which involves some noncommutative structures that prevent the sharp localization of reference frames.
Quantizing causation
Robert Spekkens
Perimeter Institute for Theoretical Physics
"Spatiotemporal relations are often taken to be more primitive than causal relations. Such a relationship is assumed whenever it is suggested that it is part of the definition of a causal relation that the cause must precede the effect in time. There are good reasons, however, to take causation to be the more primitive notion, with spatiotemporal relations merely describing aspects of causal relations.
Noncausal PageWootters circuits
Veronika Baumann
Institute for Quantum Optics and Quantum Information (IQOQI)  Vienna
"The process matrix framework was invented to capture a phenomenon known as indefinite or quantum causal structure. Due to the generality of that framework, however, for many process matrices there is no clear physical interpretation. A popular approach towards a quantum theory of gravity is the PageWootters formalism, which associates to time a Hilbert space structure similar to spatial position. By explicitly introducing a quantum clock, it allows to describe timeevolution of systems via correlations between this clock and said systems encoded in history states.
Quantum reference frames for space and spacetime
Časlav Brukner
Universität Wien
In physics, a reference frame is an abstract coordinate system that specifies observations within that frame. While quantum states depend on the choice of reference frame, the form of physical laws is assumed to be covariant. Recently, it has been proposed to consider reference frames as physical systems and as such assume that they obey quantum mechanics. In my talk, I will present recent results in the field of "quantum reference frames" (QRF).
A New Perspective on Time Reversal Motivated by Quantum Gravity
Abhay Ashtekar
Pennsylvania State University
Time Reversal T is usually discussed in the traditional framework of quantum mechanics in which T is represented by an antiunitary operator. But quantum gravity may well need generalization of standard quantum mechanics which may not preserve even its linear structure, let alone the unitarity of dynamics and antiunitarity of T. Then the currently used arguments to conclude that T violation is a fundamental aspect of Nature will break down.
Space and Time in a Lorentzian path integral
Bianca Dittrich
Perimeter Institute for Theoretical Physics
I will present a quantum gravity approach based on a Lorentzian path integral for quantum geometries. The properties of quantum space time can be measured using geometric operators. This allows also to discuss fluctuations of causal structure as well as violations of (micro) causality. I will explain how the Lorentzian path integral comes with various options regarding which quantum space times to sum over: e.g. whether to include causality violations or not, or whether to allow also for space times with Euclidean signatures in Lorentzian path integrals.
"TIME IN QUANTUM GRAVITY  From the fundamental level to the classical limit"
Claus Kiefer
Universität zu Köln
Time cannot be both absolute (as in quantum mechanics) and dynamical (as in general relativity). I present general arguments for the absence of time at the most fundamental level of quantum gravity. I discuss possible concepts that could replace it and present the recovery of standard time as an approximate concept. My discussion is restricted to quantum geometrodynamics, but I argue for the validity of my conclusions beyond that scheme.