Virtual Seminars

It has been occasionally remarked, but insufficiently appreciated, that there are two distinct sorts of endeavour that have gone by the name of “thermodynamics”. The first, which is in line with how the founders of the subject thought of it, is a theory about how agents with limited means of manipulation and limited access to …

Wayne Myrvold
Western UniversityA Tale of Two Sciences, Both Called “Thermodynamics” Read More »

John Wheeler was the inventor of quantum gravity – not as a formal program for uniting general relativity and quantum mechanics, but as the potential key to a theory of everything. In this talk, I will show how he first imbued quantum gravity with this new role in the 1950s and then how (and why) …

Alexander Blum
Max Planck Institute for the History of ScienceJohn Wheeler and Quantum Gravity Read More »

I intend to discuss the implications of the principle of locality for interference in quantum field theory. As an example, I will consider the interaction of two charges via a mediating quantum field and the resulting interference pattern, in the Lorenz gauge. Using the Heisenberg picture, I will claim that detecting relative phases or entanglement between …

Vlatko Vedral
University of Oxford Interference in quantum field theory: detecting ghosts with phases Read More »

Testing the quantum character of weak forces such as gravity requires both exquisite experimental control of technology and careful design by theory of the experiment set-up. At the same time, the interpretation of experiments that probe the interface between quantum physics and gravity also mandates that we examine carefully all the assumptions, however innocuous, that …

Martin Plenio
Ulm UniversityTesting of Quantum Aspects of Gravity at Low Energies: Discussion of Experiment Aspects and Possible Loopholes Read More »

It is well known that, even the simplest states within the simplest field theories, are highly entangled. The main support for this fact comes from calculations of entanglement entropy between a region of space and its complement. I find two uncomfortable facts in the calculation of such entropy: (i) The result is actually infinite, and …

Ivan Agullo
Louisiana State UniversityEntanglement in quantum field theory Read More »

A non-relativistic limit of twistor theory provides a non-local description of Newtonian space-times. It is argued that combining this non–locality 
with the non–locality of quantum mechanics provides a mechanism for Penrose’s proposal linking classical gravity and quantum wave function collapse.

Abstract:
The formalism of quantum theory over discrete systems is extended in two significant ways. First, tensors and traceouts are generalized, so that systems can be partitioned according to almost arbitrary logical predicates. Second, quantum evolutions are generalized to act over network configurations, in such a way that nodes be allowed to merge, split and reconnect coherently in a superposition. The hereby presented mathematical framework is anchored on solid grounds through numerous lemmas. Indeed, one might have feared that the familiar interrelations between the notions of unitarity, complete positivity, trace-preservation, non-signalling causality, locality and localizability that are standard in quantum theory be jeopardized as the partitioning of systems becomes both logical and dynamical. Such interrelations in fact carry through.
(Joint work with Amélia Durbec and Matt Wilson, reference: https://arxiv.org/abs/2110.10587

I provide a conceptually-focused presentation of `low-energy quantum gravity’ (LEQG), the effective quantum field theory obtained from general relativity and which provides a well-defined theory of quantum gravity at energies well below the Planck scale. I emphasize the extent to which some such theory is required by the abundant observational evidence in astrophysics and cosmology …

David Wallace
Pittsburg UniversityQuantum gravity at low energies Read More »

Don Marolf will review and summarize recent developments regarding spacetime wormholes in the gravitational path integral and their implications for the existence of a certain notion of “superselection sectors” in quantum gravity.  The existence of such sectors implies that, in certain contexts, we can think of quantum gravity as describing a statistical ensemble of theories.  …

Don Marolf
University of California Santa Barbara Spacetime wormholes, superselection sectors, and ensembles in quantum gravity: An Overview Read More »

Due to rapid progress in experimental quantum information science, a table-top test of quantum gravity may soon be possible. A promising possibility is to place two micro-solids in a spatial superposition and separable state. If, after a short time, entanglement between the micro-solids is observed then this could provide evidence of a quantum theory of gravity, assuming all other interactions can be neglected and that gravity provides a local interaction. These proposals have raised a number of questions, such as whether entanglement generation would really provide a test of quantum gravity and whether the experiments are feasible in the near term. Here, we consider whether an alternative signature of quantum gravity to entanglement could be used for a table-top test, and an alternative experimental setting. Specifically, we consider non-Gaussianity rather than entanglement and how this could be searched for in a Bose-Einstein condensate (BEC) to evidence quantum gravity. We discuss whether using non-Gaussianity and a BEC could provide any advantages to entanglement and micro-solids.