UCSD Mini-Workshop on Quantum Foundations
Time: May 27, 2025
Conference location:
Department Library Room 0427, Department of Philosophy, University of California, San Diego, CA
Arts and Humanities Building, 4th Floor
9625 Scholars Drive North, La Jolla CA 92093
Conference location:
Department Library Room 0427, Department of Philosophy, University of California, San Diego, CA
Arts and Humanities Building, 4th Floor
9625 Scholars Drive North, La Jolla CA 92093
Tuesday, May 27
10:00–11:20 Ken Wharton: Bell's Theorem and Retrocausality (research talk)
11:30–12:50 Elias Okon: On real-but-undetectable entities: the cases of Newtonian absolute velocity and Bohmian positions (research talk)
1:00–2:00 Lunch
2:00–3:20 Emily Adlam: What can a qubit observe? (research talk)
3:45–4:45 Elias Okon: On the objectivity of measurement outcomes (Intro class)
5:00–6:00 Ken Wharton: Retrocausal Models of Entanglement (Intro class)
7:00 Dinner
10:00–11:20 Ken Wharton: Bell's Theorem and Retrocausality (research talk)
11:30–12:50 Elias Okon: On real-but-undetectable entities: the cases of Newtonian absolute velocity and Bohmian positions (research talk)
1:00–2:00 Lunch
2:00–3:20 Emily Adlam: What can a qubit observe? (research talk)
3:45–4:45 Elias Okon: On the objectivity of measurement outcomes (Intro class)
5:00–6:00 Ken Wharton: Retrocausal Models of Entanglement (Intro class)
7:00 Dinner
Organizer: Eddy Keming Chen (UCSD)
This workshop is made possible through the John Templeton Foundation grant "SoCal Quantum Foundations Hub: Knowledge and Agency in Quantum Theory."
Practical information:
Conference hotel: La Jolla Shores Hotel (8110 Camino Del Oro, La Jolla, CA 92037)
Conference attendance is free. All are welcome!
Talk abstracts:
Bell's Theorem and Retrocausality
Ken Wharton, San Jose State University
Abstract: Combined with quantum entanglement experiments, Bell's Theorem has long proved that we can't have nice things when it comes to space, time, and causality. But it is now becoming widely appreciated that we can still demand locally-mediated influences if we are willing to allow for hidden retrocausality. This talk will describe the various motivations for developing retrocausal / “all at once” models of quantum phenomena, qualitatively describe how such models would work, and summarize their prospects for restoring a spacetime-based reality to fundamental physics.
(Based on: K.B. Wharton and N. Argaman, "Bell's theorem and locally mediated reformulations of quantum mechanics", Rev. Mod. Phys. v92, 21002 (2020). arXiv: 1906.04313)
On real-but-undetectable entities: the cases of Newtonian absolute velocity and Bohmian positions
Elias Okon (UNAM)
Abstract: It is not uncommon for a physical theory to postulate the existence of something, only to later argue it to be undetectable according to the theory itself. For instance, the original Newtonian mechanics postulates the existence of absolute velocity, but such property is then argued to be undetectable. Similarly, pilot-wave theory postulates the existence of particle positions, but the theory is said to impose strict limits to their detection. In this talk, I will argue that the derivations of this sort of undetectability claims generically depend upon unjustified assumptions regarding what degrees of freedom are able to encode detection results. I conclude that one must always treat with suspicion any claim within a physical theory regarding the existence of real-but-undetectable entities.
What can a qubit observe?
Emily Adlam (Chapman)
Abstract: In the context of relational quantum mechanics and more generally in the study of quantum reference frames, it is common to describe the state of a quantum system relative to a small quantum system such as a qubit. However there are significant difficulties for current formalisms, because they do not take into account the actual physical resources available to such a system. In this talk I will suggest how we can use some tools from the quantum reference frame program and group theory to characterise these physical resources and get a better understanding of the state of one system relative to another.
On the objectivity of measurement outcomes
Elias Okon (UNAM)
Abstract: Recent arguments, involving entangled systems shared by sets of Wigner’s friend arrangements, allegedly show that the assumption that the experiments performed by the friends yield definite outcomes, is incompatible with quantum predictions. From this, it is concluded that the results of measurements cannot be thought of as being actual or objective. Here, I show that these arguments depend upon a mistaken assumption, regarding the (“mixed”) correlations between the results of the friends and those of “the Wigners”, which leads to invalid predictions. It is not, then, that the assumption of definite outcomes leads to trouble, but that the results derived with such an assumption are contrasted with faulty predictions. Next, I explore the more famous no-go theorem by Frauchiger and Renner, on which these recent arguments are motivated. I show that, although it is cast in a different form, it also rests on the mistaken assumption regarding “mixed” correlations—rendering it invalid. Throughout, I illustrate my claims with explicit calculations within pilot-wave theory.
Retrocausal Models of Entanglement
Ken Wharton, San Jose State University
Abstract: Explaining quantum entanglement in a spacetime-only framework is possible using retrocausal models, where future inputs (like setting choices) constrain past hidden variables. Such approaches require an “all at once” (block-universe) mindset, using global constraints which are difficult to understand without explicit examples. In this talk, at least two models in this category will be described in detail. First, the Schulman model, which can correctly generate the probabilities for all maximally-entangled 2-qubit states (and has recently been extended to GHZ 3-qubit states). Second, progress will be reported on a new model based on quantum circuits, in which even partially-entangled states can be analyzed. Relevant techniques for solving two-time boundary problems will also be described.
See https://arxiv.org/abs/1510.03706 , https://arxiv.org/abs/2401.09398 (Schulman Model) and https://arxiv.org/abs/2412.05456 (circuit model)
This workshop is made possible through the John Templeton Foundation grant "SoCal Quantum Foundations Hub: Knowledge and Agency in Quantum Theory."
Practical information:
Conference hotel: La Jolla Shores Hotel (8110 Camino Del Oro, La Jolla, CA 92037)
Conference attendance is free. All are welcome!
Talk abstracts:
Bell's Theorem and Retrocausality
Ken Wharton, San Jose State University
Abstract: Combined with quantum entanglement experiments, Bell's Theorem has long proved that we can't have nice things when it comes to space, time, and causality. But it is now becoming widely appreciated that we can still demand locally-mediated influences if we are willing to allow for hidden retrocausality. This talk will describe the various motivations for developing retrocausal / “all at once” models of quantum phenomena, qualitatively describe how such models would work, and summarize their prospects for restoring a spacetime-based reality to fundamental physics.
(Based on: K.B. Wharton and N. Argaman, "Bell's theorem and locally mediated reformulations of quantum mechanics", Rev. Mod. Phys. v92, 21002 (2020). arXiv: 1906.04313)
On real-but-undetectable entities: the cases of Newtonian absolute velocity and Bohmian positions
Elias Okon (UNAM)
Abstract: It is not uncommon for a physical theory to postulate the existence of something, only to later argue it to be undetectable according to the theory itself. For instance, the original Newtonian mechanics postulates the existence of absolute velocity, but such property is then argued to be undetectable. Similarly, pilot-wave theory postulates the existence of particle positions, but the theory is said to impose strict limits to their detection. In this talk, I will argue that the derivations of this sort of undetectability claims generically depend upon unjustified assumptions regarding what degrees of freedom are able to encode detection results. I conclude that one must always treat with suspicion any claim within a physical theory regarding the existence of real-but-undetectable entities.
What can a qubit observe?
Emily Adlam (Chapman)
Abstract: In the context of relational quantum mechanics and more generally in the study of quantum reference frames, it is common to describe the state of a quantum system relative to a small quantum system such as a qubit. However there are significant difficulties for current formalisms, because they do not take into account the actual physical resources available to such a system. In this talk I will suggest how we can use some tools from the quantum reference frame program and group theory to characterise these physical resources and get a better understanding of the state of one system relative to another.
On the objectivity of measurement outcomes
Elias Okon (UNAM)
Abstract: Recent arguments, involving entangled systems shared by sets of Wigner’s friend arrangements, allegedly show that the assumption that the experiments performed by the friends yield definite outcomes, is incompatible with quantum predictions. From this, it is concluded that the results of measurements cannot be thought of as being actual or objective. Here, I show that these arguments depend upon a mistaken assumption, regarding the (“mixed”) correlations between the results of the friends and those of “the Wigners”, which leads to invalid predictions. It is not, then, that the assumption of definite outcomes leads to trouble, but that the results derived with such an assumption are contrasted with faulty predictions. Next, I explore the more famous no-go theorem by Frauchiger and Renner, on which these recent arguments are motivated. I show that, although it is cast in a different form, it also rests on the mistaken assumption regarding “mixed” correlations—rendering it invalid. Throughout, I illustrate my claims with explicit calculations within pilot-wave theory.
Retrocausal Models of Entanglement
Ken Wharton, San Jose State University
Abstract: Explaining quantum entanglement in a spacetime-only framework is possible using retrocausal models, where future inputs (like setting choices) constrain past hidden variables. Such approaches require an “all at once” (block-universe) mindset, using global constraints which are difficult to understand without explicit examples. In this talk, at least two models in this category will be described in detail. First, the Schulman model, which can correctly generate the probabilities for all maximally-entangled 2-qubit states (and has recently been extended to GHZ 3-qubit states). Second, progress will be reported on a new model based on quantum circuits, in which even partially-entangled states can be analyzed. Relevant techniques for solving two-time boundary problems will also be described.
See https://arxiv.org/abs/1510.03706 , https://arxiv.org/abs/2401.09398 (Schulman Model) and https://arxiv.org/abs/2412.05456 (circuit model)