Foil theories sometimes called mathematically rigorous science fiction describe ways the world could have been were it not quantum mechanical. Our understanding of quantum theory has been deepened by contrasting it with these alternatives. So far observers in foil theories have only been modeled implicitly for example via the recorded probabilities of observing events. Even when multiagent settings are considered these agents tend to be compatible in the classical sense that they could always compare their observations. Scenarios where agents and their memories are themselves modeled as physical systems within the theory (and could in particular measure each other as in Wigner's friend experiment) have not yet been considered. In this workshop we will investigate which foil theories allow for the existence of explicit observers and whether they allow for paradoxes in multiagent settings such as those found in quantum theory. We will also investigate which interpretations of quantum theory would equally well interpret the foil theories and which interpretations are truly quantum. We will gain a deeper understanding of how this can happen by discussing appropriate definitions observers in these theories and seeing how such observers learn about their environment.
Format results

Wavefunction branches as a foundation for constructing foil theories
Jess Riedel NTT Research
PIRSA:18040082 
Compatibility of implicit and explicit observers in quantum theory and beyond
Thomas Galley Perimeter Institute for Theoretical Physics
PIRSA:18040084 
From observers to physics via algorithmic information theory I
Markus Mueller Institute for Quantum Optics and Quantum Information (IQOQI)  Vienna
PIRSA:18040078 
From observers to physics via algorithmic information theory II
Markus Mueller Institute for Quantum Optics and Quantum Information (IQOQI)  Vienna
PIRSA:18040080 
Motility of the internalexternal cut as a foundational principle
Robert Spekkens Perimeter Institute for Theoretical Physics
PIRSA:18040073 

Quantum theory cannot consistently describe the use of itself
Renato Renner ETH Zurich  Institut für Theoretische Physik
PIRSA:18040085 
Inadequacy of modal logic in quantum settings
Lidia del Rio ETH Zurich  Institut für Theoretische Physik
PIRSA:18040087 

Agents, Subsystems, and the Conservation of Information
Giulio Chiribella The University of Hong Kong (HKU)
PIRSA:18040089 
Microcanonical thermodynamics in general physical theories
Carlo Maria Scandolo University of Oxford
PIRSA:18040091