Observers in Quantum and Foil Theories

Conference Date: 
Monday, April 2, 2018 (All day) to Friday, April 6, 2018 (All day)
Scientific Areas: 
Quantum Foundations

 

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 multi-agent 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 multi-agent 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.

Sponsorship for this workshop has been provided by:

  • Giulio Chiribella, University of Oxford
  • Lidia del Rio, ETH Zurich
  • Thomas Galley, University College London
  • Markus Mueller, Perimeter Institute & Institute for Quantum Optics and Quantum Information, Vienna
  • Renato Renner, ETH Zurich
  • Jess Riedel, Perimeter Institute
  • Carlo Maria Scandolo, University of Oxford
  • Ruediger Schack, Royal Holloway University of London
  • Rob Spekkens, Perimeter Institute
  • Joel Wallman, University of Waterloo
  • Giulio Chiribella, University of Oxford
  • Thomas Galley, University College London
  • Ravi Kunjwal, Perimeter Institute
  • Markus Mueller, Perimeter Institute & Institute for Quantum Optics and Quantum Information, Vienna
  • Renato Renner, ETH Zurich
  • Jess Riedel, Perimeter Institute
  • Nitica Sakharwade, Perimeter Institute
  • Carlo Maria Scandolo, University of Oxford
  • Ruediger Schack, Royal Holloway University of London
  • David Schmid, Perimeter Institute
  • John Selby, Perimeter Institute
  • Rob Spekkens, Perimeter Institute
  • Joel Wallman, University of Waterloo

Monday, April 2, 2018

Time

Event

Location

10:00 – 10:30am

Registration

Reception

 

WHAT IS QUANTUM

 

10:30 – 11:30am

Jess Riedel, Perimeter Institute
Wavefunction branches as a foundation for constructing foil theories

Bob Room

11:30 – 12:00pm

Coffee Break

Bistro – 1st Floor

12:00 – 1:00pm

Discussion 1

Bob Room

1:00 – 2:30pm

Lunch

Bistro – 1st Floor
Reserved Table

2:30 – 3:30pm

Thomas Galley, University College London
Compatibility of implicit and explicit observers in quantum theory and beyond

Bob Room

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 5:00 pm

Discussion 2

Bob Room

 

Tuesday, April 3, 2018

Time

Event

Location

 

INFORMATION ACQUSITION

 

10:30 – 11:30am

Markus Mueller, Perimeter Institute and Institute for Quantum Optics and Quantum Information, Vienna
From observers to physics via algorithmic information theory I

Bob Room

11:30 – 12:00pm

Coffee Break

Bistro – 1st Floor

12:00 – 1:00pm

Discussion 3

Reflecting Lounge

1:00 – 2:30pm

Lunch

Bistro – 1st Floor
Reserved Table

2:30 – 3:30pm

Markus Mueller, Perimeter Institute and Institute for Quantum Optics and Quantum Information, Vienna
From observers to physics via algorithmic information theory II

Bob Room

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 4:30pm

Discussion 4

Reflecting Lounge

 

Wednesday, April 4, 2018

Time

Event

Location

 

FOILS AND OTHER MODELS

 

10:30 – 11:30am

Rob Spekkens, Perimeter Institute
Motility of the internal-external cut as a foundational principle

Bob Room

11:30 – 12:00pm

Coffee Break

Bistro – 1st Floor

12:00 – 1:00pm

Discussion 5

Reflecting Lounge

1:00 – 2:00pm

Lunch

Bistro – 1st Floor
Reserved Table

2:00 – 3:30pm

Colloquium
Kendrick Smith, Perimeter Institute
CHIME: the Canadian Hydrogen Intensity Mapping Experiment

Time Room

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 5:30pm

Joel Wallman, University of Waterloo
TBA

Bob Room

 

Thursday, April 5, 2018

Time

Event

Location

 

PARADOXES & INTERPRETATIONS

 

10:30 – 11:30am

Renato Renner, ETH Zurich
Quantum theory cannot consistently describe the use of itself

Bob Room

11:30 – 12:00pm

Coffee Break

Bistro – 1st Floor

12:00 – 1:00pm

Discussion 6

Reflecting Lounge

1:00 – 2:30pm

Lunch

Bistro – 1st Floor
Reserved Table

2:30 – 3:30pm

Lidia del Rio, ETH Zurich
TBA

Bob Room

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 5:00pm

Ruediger Schack, Royal Holloway University of London
QBism and Wigner's friend

Bob Room

6:00 – 8:00pm

Banquet

Bistro – 2nd Floor

 

Friday, April 6, 2018

Time

Event

Location

 

CAUSALITY?

 

10:30 – 11:30am

Giulio Chiribella, University of Oxford
Agents, Subsystems, and the Conservation of Information

Bob Room

11:30 – 12:00pm

Coffee Break

Bistro – 1st Floor

12:00 – 1:00pm

Discussion 7

Reflecting Lounge

1:00 – 2:30pm

Lunch
Please note that a lunchtime concert will be performed in the atrium from 1:00 – 2:00 pm.  All are welcome.

Bistro – 1st Floor
Reserved Table

2:30 – 3:30pm

Carlo Maria Scandolo, University of Oxford
Microcanonical thermodynamics in general physical theories

Bob Room

3:30 – 4:00pm

Coffee Break

Bistro – 1st Floor

4:00 – 5:00pm

Wrap Up and Good-Bye

Bob Room

 

 

 

Giulio Chiribella, University of Oxford

Agents, Subsystems, and the Conservation of Information

Dividing the world into subsystems is an important component of the scientific method. The choice of subsystems, however, is not defined a priori. Typically, it is dictated by our experimental capabilities, and, in general, different agents may have different capabilities. Here we propose a construction that associates every agent with a subsystem, equipped with its set of states and its set of transformations. In quantum theory, this construction accommodates the traditional notion of subsystems as factors of a tensor product, as well as the notion of classical subsystems of quantum systems. We then restrict our attention to systems where all physical transformations act invertibly. For such systems, the future states are a faithful encoding of the past states, in agreement with a requirement known as the Conservation of Information. For systems satisfying the Conservation of Information, we propose a dynamical definition of pure states, and show that all the states of all subsystems admit a canonical purification. This result extends the purification principle to a broader setting, in which coherent superpositions can be interpreted as purifications of incoherent mixtures. As an example, we illustrate the general construction for subsystems associated with group representations.

Thomas Galley, University College London

Compatibility of implicit and explicit observers in quantum theory and beyond

The observer is implicitly present in the measurement postulates of quantum theory. However the observer can also be modeled as a quantum system interacting with other quantum systems. A theory where every action implicitly undertaken by an agent (such as a measurement or preparation) can be explicitly modeled as non-classical systems interacting is called a universal theory. By modifying the measurement postulates of quantum theory (and preserving the other postulates) we create theories where the observer can still be explicitly modeled as a pure quantum state, but where the implicit observer is different. We argue that any modification of the measurement postulates of quantum theory gives a theory which is not universal. That is to say there are certain actions implicitly carried out by an agent which cannot be explicitly modeled.

Markus Mueller, Perimeter Institute and Institute for Quantum Optics and Quantum Information, Vienna

From observers to physics via algorithmic information theory I & II

Motivated by the conceptual puzzles of quantum theory and related areas of physics, I describe a rigorous and minimal “proof of principle” theory in which observers are fundamental and in which the physical world is a (provably) emergent phenomenon. This is a reversal of the standard view, which holds that physical theories ought to describe the objective evolution of a unique external world, with observers or agents as derived concepts that play no fundamental role whatsoever.

Using insights from algorithmic information theory (AIT), I show that this approach admits to address several foundational puzzles that are difficult to address via standard approaches. This includes the measurement and Boltzmann brain problems, and problems related to the computer simulation of observers. Without assuming the existence of an external world from the outset, the resulting theory actually predicts that there is one as a consequence of AIT — in particular, a world with simple, computable, probabilistic laws on which different observers typically (but not always) agree. This approach represents a consistent but highly unfamiliar picture of the world, leading to a new perspective from which to approach some questions in the foundations of physics.
 
Renato Renner, ETH Zurich
 
Quantum theory cannot consistently describe the use of itself
 
Jess Riedel, Perimeter Institute
 
Wavefunction branches as a foundation for constructing foil theories
 
Carlo Maria Scandolo, University of Oxford
 
Microcanonical thermodynamics in general physical theories
 
Microcanonical thermodynamics studies the operations that can be performed on systems with well-defined energy. So far, this approach has been applied to classical and quantum systems. Here we extend it to arbitrary physical theories, proposing two requirements for the development of a general microcanonical framework. We then formulate three resource theories, corresponding to three different choices of basic operations. We focus on a class of physical theories, called sharp theories with purification, where these three sets of operations exhibit remarkable properties. In these theories, a necessary condition for thermodynamic transitions is given by a suitable majorisation criterion. This becomes a sufficient condition in all three resource theories if and only if the dynamics allowed by the theory satisfy a condition that we call "unrestricted reversibility". Under this condition, we derive a duality between the resource theory of microcanonical thermodynamics and the resource theory of pure bipartite entanglement.
 
Ruediger Schack, Royal Holloway University of London
 
QBism and Wigner's friend
 
Kendrick Smith, Perimeter Institute
 
CHIME: the Canadian Hydrogen Intensity Mapping Experiment
 
CHIME is a new interferometric telescope at radio frequencies 400-800 MHz. The mapping speed (or total statistical power) of CHIME is among the largest of any radio telescope in the world, and the technology powering CHIME could be used to build telescopes which are orders of magnitude more powerful. This breakthrough sensitivity has the power to revolutionize radio astronomy, but meeting the computational challenges will require breakthroughs on the algorithmic side.  I'll give a status update on CHIME, with an emphasis on new algorithms developed at Perimeter to search for fast radio bursts (FRB's) and pulsars.
 
Rob Spekkens, Perimeter Institute
 
Motility of the internal-external cut as a foundational principle
 

 

Friday Apr 06, 2018
Speaker(s): 

Microcanonical thermodynamics studies the operations that can be performed on systems with well-defined energy. So far, this approach has been applied to classical and quantum systems. Here we extend it to arbitrary physical theories, proposing two requirements for the development of a general microcanonical framework. We then formulate three resource theories, corresponding to three different choices of basic operations. We focus on a class of physical theories, called sharp theories with purification, where these three sets of operations exhibit remarkable properties.

 

Friday Apr 06, 2018
Speaker(s): 

Dividing the world into subsystems is an important component of the scientific method. The choice of subsystems, however, is not defined a priori. Typically, it is dictated by our experimental capabilities, and, in general, different agents may have different capabilities. Here we propose a construction that associates every agent with a subsystem, equipped with its set of states and its set of transformations.

 

Thursday Apr 05, 2018
Speaker(s): 

 

Wednesday Apr 04, 2018
Speaker(s): 

 

Tuesday Apr 03, 2018
Speaker(s): 

Motivated by the conceptual puzzles of quantum theory and related areas of physics, I describe a rigorous and minimal “proof of principle” theory in which observers are fundamental and in which the physical world is a (provably) emergent phenomenon. This is a reversal of the standard view, which holds that physical theories ought to describe the objective evolution of a unique external world, with observers or agents as derived concepts that play no fundamental role whatsoever.

 

Monday Apr 02, 2018
Speaker(s): 

The observer is implicitly present in the measurement postulates of quantum theory. However the observer can also be modeled as a quantum system interacting with other quantum systems. A theory where every action implicitly undertaken by an agent (such as a measurement or preparation) can be explicitly modeled as non-classical systems interacting is called a universal theory.

Pages

Scientific Organizers:

  • Lidia del Rio, ETH Zurich
  • Matthew Pusey, University of Oxford
  • Ana Belen Sainz, Perimeter Institute