The aim of the workshop is to discuss the main philosophical implications of the spontaneous collapse models (SCM) of quantum mechanics. Since they were first proposed in the late '80s, the SCM have been among the most discussed solutions to the measurement problem. In this workshop, some of the main figures in the debate on these models (both physicists such as Bassi and Sudarsky, as well as philosophers like Albert, Allori, Egg, and Maudlin) will discuss the viability, the future prospects, and the ontological consequences of SCM. The workshop is organised within Cristian Mariani SNF Ambizione project 'Quantum Indeterminacy'.

Date:

**20 – 21 May 2024**

Venue:

Room A-31, Red Building (Monday 20th)

Room 2.2, FTL Building (Tuesday 21th)

USI West Campus, Via Buffi 13

Lugano, Switzerland

This workshop will also be streamed on Zoom, to get the link, write to: events.isfi@usi.ch

Speakers:

David Albert (Columbia)

Valia Allori (Bergamo)

Angelo Bassi (Trieste)

Matthias Egg (Bern)

Tim Maudlin (NYU)

Daniel Sudarsky (UNAM)

Programme:

**Monday 20th (A-31 red building, USI Campus)**

09.00 - 9.15 Introduction

09.15 - 11.00 Tim Maudlin (NYU) Spontaneous Collapse: Achievements and Challenges

11.00 - 11.15 Coffee break

11.15 - 13.00 Matthias Egg (Bern) Non-fundamental Local Beables for Spontaneous Collapse Models

14.30 - 16.15 Daniel Sudarsky (UNAM) Spontaneous Collapse theories in Gravitational Contexts

16.15 - 16.30 Coffee break

16.30 - 18.15 Valia Allori (Bergamo) What is it Like to be a Relativistic GRW Theory? Or: Quantum Mechanics and Relativity, Still in Conflict After All These Years

**Tuesday 21st (2.2 FTL building, USI Campus)**

09.15 - 11.00 Angelo Bassi (Trieste) Do wave functions jump?

11.00 - 11.15 Coffee break

11.15 - 13.00 David Albert (Columbia) The GRW Theory and the Future of Physics

Abstracts:

David Albert — The GRW Theory and the Future of Physics

Abstract: I will discuss two very different kinds of impact that the GRW theory might conceivably have on the future of physics: The GRW theory can offer hints about where to look for possible observable violations of Lorentz Invariance, and it offers a way of tracing all of the probabilities in the world - both in fundamental physics and in the special sciences - back to a single, simple, source.

Valia Allori — What is it Like to be a Relativistic GRW Theory? Or: Quantum Mechanics and Relativity, Still in Conflict After All These Years

The violation of Bell’s inequality has shown that quantum theory and relativity are in tension: reality is nonlocal. Nonetheless, many have argued that GRW-type theories are to be preferred to pilot-wave theories as they are more compatible with relativity: while relativistic pilot-wave theories require a preferred slicing of space-time, foliation free relativistic GRW-type theories have been proposed. In this paper I discuss various meanings of ‘relativistic invariance,’ and I show how GRW-type theories, while being more relativistic in one sense, are less relativistic in another. If so, the initial claim that GRW-type theories have a greater compatibility with relativity is unwarranted: both types of theories violate relativity, one way or another.

Angelo Bassi — Do wave functions jump?

Spontaneous wave function collapse models have been developed to account for the gradual breakdown of quantum superpositions in sufficiently large systems. These models achieve this by modifying the Schrödinger dynamics, making them subject to empirical testing. However, the deviations they predict necessitate precise measurements. In this presentation, I will overview collapse models and discuss the latest experimental tests. Additionally, I will share some insights into the worldview that emerges from these models.

Matthias Egg — Non-fundamental Local Beables for Spontaneous Collapse Models

I argue for the idea that objects and events in three-dimensional space (so-called local beables) are part of the derivative ontology of quantum mechanics, rather than its fundamental ontology. In the context of spontaneous collapse models, this means that the proposed ontologies of matter density or flashes should not be regarded as primitive, but as manifestations of the wave function in three-dimensional space. I defend this approach against several objections and place it in the larger context of effective realism, a novel view that seeks to take seriously the ontological implications of non-fundamental scientific theories.

Tim Maudlin — Spontaneous Collapse: Achievements and Challenges

Spontaneous collapse or reduction theories, such as those of Ghirardi, Rimini and Weber, of Perle, and of Penrose, clearly have the capacity to solve some of the longstanding problems of quantum physics. Because they are spontaneous rather than “measurement triggered”, they never even face the usual measurement problem. And because they are stochastic, it is obvious how probabilities arise in the theories and what the probabilities are for. But there still remain serious issues to be addressed. A central one is the status of “local beables” in these theories: what exactly are they and in what space are they local? If no local beables in a macroscopically three-dimensional space exist in the theory, making contact with experimental data is a critical challenge. And if such a three-dimensional space is said to only “emerge” from the “space where the wave-function lives”, then what one even means by a fundamentally Relativistic version of the theory is obscure. I will consider these challenges.

Daniel Sudarsky — Spontaneous Collapse theories in Gravitational Contexts

We will discuss some of the complications that arise in trying to adapt spontaneous collapse theories to gravitational contexts. This might, on the one hand, seem as a rather ambitious undertaking, that could be deemed ``premature" in view of other challenges the theories still face. However I will argue that it also represents an opportunity to learn more about the versions of the theory that might be most generally viable, and at the same time it is an ``urgent task" , given the fact that some of the topics where the theories seem to display the greatest potential to address unexpected issues, lie precisely in contexts where gravitation also plays a fundamental role, like cosmology or the physics of black holes. We'll briefly discuss some recent progress in that direction.

Organiser:

Cristian Mariani with his SNF Ambizione: Quantum Indeterminacy

An event of the Institute of Philosophy (ISFI)

For any query: events.isfi@usi.ch