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Markus aspelmeyer

Lee Smolin
Perimeter Institute


The quantum universe as a collection of partial views of itself

Abstract: I describe a recent proposal for a simultaneous completion of quantum mechanics and general relativity, called the causal theory of views (CTV). Among its postulates are that time, in the sense of causal relations amongst events, is fundamental, and that space is emergent-along with everything that depends on space, such as distances, derivatives, fields, locality, non-locality etc.   Also assumed real and fundamental are energy and momentum.  Each event than has a view of the rest of the universe, which is made  by the energy and momentum transferred to it by its causal precedents. To define dynamics we must introduce a measure of distance on the space of views.  The idea is that differences of views substitutes for spacial distances and derivatives. The potential energy is then postulated to be a measure of the total diversity of views in the universe, called the variety.   The kinetic energy is then related to the variety’s rate of change under causal evolution.   The dynamics is defined by a sum over causal histories, from which space and spacetime emerge at the semiclassical approximation.  N body nonrelativistic quantum mechanics is also derived, due to the variety reducing to Bohm’s quantum potential. Further steps are sketched. Based on papers: arXiv:1712.04799.  with Marina Cortes: arXiv:1307.6167,   arXiv:1407.0032, arXiv:1703.09696 , arXiv:1902.05082,
arXiv:1104.2822, arXiv:1506.02938,  arXiv:1205.3707

Richard Healey
University of Arizona

Are facts relative in a quantum wold?

Abstract: Recent arguments purport to show that if quantum theory is universally applicable then there is no objective fact about the outcome of a quantum measurement in certain extended Wigner’s friend Gedankenexperimenten. This calls for an examination of the notions of fact and objectivity. If quantum theory is universally applicable then the facts about the physical world include a fact about each quantum measurement outcome. I will argue that these and other physical facts lack an ideal kind of objectivity but their more modest objectivity is all that science needs.

[email protected] Kong. January 13-17, 2019.

The launching workshop QISS HKU 2020 for the three year QISS project supported by the John Templeton Foundation was held at The University of Hong Kong, ​13-17 January 2020. Playlist of the videos of the talks from the workshop.  The official workshop webpage is here: www.cs.ox.ac.uk/QISS/

Časlav Brukner
University of Vienna

Quantum superposition of processes with opposing thermodynamic arrows of time

Abstract: Fundamental laws of physics are generally time-symmetric. The directionality of time is then often explained with the thermodynamic arrow of time: the entropy of an isolated system increases during a process, and it is constant only if the process is reversible. In this talk, I will consider a quantum superposition between two processes with opposing thermodynamic arrows of time. How is a definite arrow of time established for such a superposition? I will show that a quantum measurement of entropy change (for values larger than the thermal fluctuations) can be accountable for this. In particular, while the individual result of the measurement is random, once the value of the entropy variation has been observed, the system continues its evolution according to a definite arrow of time. Furthermore, for entropy variations lower than (or of the order of) the thermal fluctuations, interference effects can cause entropy changes describing more or less (ir)reversible processes than either of the two constituents, or any classical mixture therefrom.

Lucien Hardy
Perimeter Institute

A Time Symmetry in Operational Theories

Abstract: The standard framework for probabilistic operational theories is time asymmetric. The fact that future choices cannot affect the probability of earlier outcomes is mathematised by the statement that the deterministic effect is unique. However, deterministic preparations are not unique and, correspondingly, earlier choices can influence later probabilities of outcomes. This time asymmetry is rather strange because abstract probability theory knows nothing of time. Furthermore, the Schoedinger equation is time symmetric and, additionally, measurement situations can be treated by very simple models (without invoking the Second Law at all). In this talk I will outline how it is possible to give a time symmetric treatment of operational probabilistic theories with particular application to Quantum Theory. In so doing, we will see that the usual formulation of operational quantum theory is, in some sense, missing half of the picture.

Anna Pearson with Natalia Ares
Oxford University

Testing gravitational decoherence through the heating of a mechanical resonator

Abstract: The theory of classical channel gravity models gravitational interactions as classical measurement channels. These channels are a source of decoherence even if the results of the measurements are never recorded in a lab and thus the gravitational interaction can be thought of as having the same effect as an observer. This leads to two potentially observable effects – decoherence in the position basis and a density dependent heating effect. We have set up an experiment to test for the latter, using a cavity optomechanical setup at cryogenic temperatures to measure the mode heating of a silicon nitride membrane.

Nick Huggett, with Tushar Menon and Fedele Lizzi
University of Illinois

Missing the Point in Noncommutative Geometry

Abstract: Noncommutative geometries generalize standard smooth geometries, parametrizing the noncommutativity of dimensions with a fundamental quantity with the dimensions of area. The question arises then of whether the concept of a region smaller than the scale makes sense in such a theory. We argue that it does not, in two interrelated ways. In the context of Connes’ spectral triple approach, we show that arbitrarily small regions are not definable in the formal sense. While in the scalar field Moyal-Weyl approach, we show that they cannot be given an operational definition. We conclude that points do not exist, and that continuous spacetime is an appearance, in such geometries.