The Colloquium’s goal is to provide a window into the state-of-the-art in the foundations of spacetime physics. It brings together top-level philosophers and physicists willing to share their current research with an international audience.

All the meetings will be online on Zoom. If you have not registered yet, you can do so here.

You can address any query to Antonio Vassallo (antonio.vassallo@pw.edu.pl).

**Winter Semester Program:**

**22 October **(17:00-19:00 CEST)** – Gordon Belot** (University of Michigan) – “The Mach-Einstein Principle of 1917-1918.” (Slides – Watch on YouTube)

Abstract:

*In 1917 and 1918 Einstein was working on relativistic cosmology and on promoting and explaining general relativity in correspondence. During this period, the thesis that the spacetime metric should be determined by the distribution of matter played an important role in his thought. This talk is concerned with interpreting this thesis and with investigating its status in general relativity.*

**5 November **(17:00-19:00 CET)** – Robert DiSalle** (Western University) – “On the Epistemological Foundations of Space-Time Geometry.” (Watch on YouTube)

Abstract:

*According to Einstein, what was central to the motivating arguments for the general theory of relativity included not only the familiar arguments about generalizing the relativity of motion, but also the more complicated argument about the empirical content of space-time geometry. On this matter, Einstein’s views, broadly speaking, reflected the influence and insight of Poincaré and Hilbert regarding the empirical interpretation of formal structures. More specifically, however, Einstein offered a reductive analysis of the empirical foundation of geometry, that is, the argument reducing geometrical measurements to observations of “point-coincidences.” This reductive argument in turn inspired logical empiricist conceptions of the empirical content of formal theories. This paper draws a sharp contrast between such conception and the way in which the theory actually determines its characteristic theoretical magnitudes, such as the curvature of space-time. It suggests that the reductive analysis ultimately obscures the empirical significance of general relativity as a novel theory of gravity and space-time, and the nature of the evidentiary basis for this dramatic conceptual shift. I outline an alternative account of how general relativity connects with spatial and temporal measurement, based in the history of the epistemology of geometry, by extending historical analyses of spatial measurement, and of the empirical character of non-Euclidean geometry, to the analysis of curved space-time. This account suggests, more generally, an account of scientific representation, and of the links between empirical descriptions and mathematical structures, that avoids the characteristic difficulties of standard recent approaches.*

**19 November **(17:00-19:00 CET)** – Jeremy Butterfield** & **Henrique Gomes** (University of Cambridge) – “Assessing the Hole Argument.” (Slides – Watch on YouTube)

Abstract:

*We assess the hole argument in general relativity, and the related topics of the definitions of symmetries and determinism. We begin by rejecting the claim made in some recent literature that the sheer mathematics of the theory makes it mandatory to identify spacetime points “across possible worlds” by dragging along by the isomorphism. We agree that the mathematics is indifferent to the identity of points, and that in many contexts, drag-along is appropriate. But we argue that general relativity, and indeed other spacetime theories, use other means of “trans-world identification”, which we will call threading. Besides, they need to use threading, on pain of trivialising important constructions: even elementary ones like the Lie derivative.*

**3 December **(17:00-19:00 CET)** – David Albert** (Columbia University) – “Physical Laws and Physical Things.” (Watch on YouTube)

Abstract:

*I will consider several strategies for absorbing unwanted pieces of concrete physical ontology (for example: absolute/substantival Newtonian space, Maxwellian Electromagnetic fields, and especially and particularly quantum-mechanical wave-functions) into the metaphysical category of Laws. I will argue that these strategies work well for the case of Newtonian absolute space – but that they work poorly for the case of quantum-mechanical wave-functions.*

**17 December **(17:00-19:00 CET)** – Alastair Wilson** (University of Birmingham) – “Fundamentality and Levels in Everettian Quantum Mechanics.” (Handout – Watch on YouTube)

Abstract:

*Distinctions in fundamentality between different levels of description are central to the viability of contemporary decoherence-based Everettian quantum mechanics (EQM). This approach to quantum theory characteristically combines a determinate fundamental reality (one universal wavefunction) with an indeterminate emergent reality (multiple decoherent worlds). In this talk I explore how the Everettian appeal to fundamentality and emergence can be understood within existing metaphysical frameworks, identify grounding and concept fundamentality as promising theoretical tools, and use them to characterize a system of explanatory levels (with associated laws of nature) for EQM. This Everettian level structure encompasses and extends the ‘classical’ levels structure. The ‘classical’ levels of physics, chemistry, biology, etc. are recovered, but they are emergent in character and potentially variable across Everett worlds. EQM invokes an additional fundamental level, not present in the classical levels picture, and a novel potential role for self-location in interlevel metaphysics. When given a modal realist interpretation, EQM also makes trouble for supervenience-based approaches to levels.*

**7 January **(17:00-19:00 CET)** – Elise Crull **(City University New York) – “You’re a Good Man, Harvey Brown: Quantum Rods & Clocks from Decoherence.” (**Talk canceled**)

Abstract:

*Harvey Brown’s 2005 book Physical Relativity calls for the development of a constructive-theoretic (as opposed to principle-theoretic) interpretation of relativity: in short, for a quantum-dynamical description of rods and clocks. Significant issues, however, stand in the way of this project. For one, such an interpretation of GR will require carrying over the Strong Equivalence Principle from SR, and this is not trivial. For another, a quantum-dynamical GR is clearly in tension with the fact that the fields in Einstein’s field equations are classical. In this talk, I argue that these issues may be dissolved by appeal to decoherence — and this prior to having in hand a fully realized theory of quantum gravity. *

**21 January **(17:00-19:00 CET)** – Richard Dawid** (Stockholm University) – “Chronical Incompleteness and Finality in String Theory.” (Watch on YouTube)

Abstract:

*String theory has not come close to a complete formulation after half a century of intense research. On the other hand, a number of features of the theory suggest that the theory, once completed, may be a final theory. It is argued in this talk that those two conspicuous characteristics of string physics are related to each other. The property that links them together is the fact that string theory has no free parameters at a fundamental level. The talk will discuss what finality could mean under the given circumstances and will look at possible implications of this situation for the long term prospects of theory building in fundamental physics.*

**Summer Semester Program:**

**25 February** (17:00-19:00 CET) – **John Norton** (University of Pittsburgh) – “Eternal Inflation: When Probabilities Fail.” (Watch on YouTube)

Abstract:

*In eternally inflating cosmology, infinitely many pocket universes are seeded. Attempts to show that universes like our observable universe are probable amongst them have failed, since no unique probability measure is recoverable. This lack of definite probabilities is taken to reveal a complete predictive failure. Inductive inference over the pocket universes, it would seem, is impossible. I argue that this conclusion of impossibility mistakes the nature of the problem. It confuses the case in which no inductive inference is possible, with another in which a weaker inductive logic applies. The alternative, applicable inductive logic is determined by background conditions and is the same, non-probabilistic logic as applies to an infinite lottery. This inductive logic does not preclude all predictions, but does affirm that predictions useful to deciding for or against eternal inflation are precluded.*

**11 March** (17:00-19:00 CET) – **Claudio Calosi** (University of Geneva) – “Out of All the Indifferences, Into One Thing: Wavefunction Monism.” (Watch on YouTube)

Abstract:

*Wavefunction Monism is a peculiar combination of monism and realism about the wavefunction. I provide the first systematic assessment of the view, highlighting benefits and costs. This assessment, I contend, sheds new light on different forms of (quantum) monism.*

**25 March** (17:00-19:00 CET) – **Samuel Fletcher** (University of Minnesota, Twin Cities) – “What Gravitational Waves Really Teach Us about Energy.” (Watch on YouTube)

Abstract:

*Gravitational wave solutions to the Einstein field equation of general relativity are commonly regarded as examples proving how gravity in general relativity transmits energy from a source body to a distant body. The famous 1955 Feynman sticky bead thought experiment illustrates the reality of this phenomenon by imagining two beads generating heat in a rod on which they slide with friction, due to their changing proper distance in the presence of the waves. I argue that while this lesson is not entirely wrong, it is much too simplistic. It does not reconcile its conclusion with the fact that conservation of local energy-momentum, in the sense that appears in the field equation, prevents energy transmission across a vacuum. Thus “energy transmission” must employ a different concept of energy, raising the possibility of pluralism with regard to the energy concept. Another (compatible) possibility is that gravitational waves, rather than transmitting energy, facilitate the transformation between different types or stores of energy locally. Key to these possibilities is analysis of the Weyl tensor. Time permitting, I discuss these possibilities’ implications for a re-evaluation of the scope of Mach’s Principle, the idea that the distribution of matter determines the geometry of spacetime.*

**8 April** (17:00-19:00 CEST) – **Nick Huggett** (University of Illinois Chicago) – “Quantum Gravity in a Laboratory?” (Slides – Watch on YouTube)

Abstract:

*The characteristic – Planck – energy scale of quantum gravity is utterly beyond current technology, making experimental access to the relevant physics apparently impossible. Nevertheless, low energy experiments linking gravity and the quantum have been undertaken: the Page and Geilker quantum Cavendish experiment, and the Colella-Overhauser-Werner neutron interferometry experiment, say. However, neither probes states in which gravity remains in a coherent quantum superposition – unlike recent proposals that have created considerable interest among physicists. In essence, if two initially unentangled systems interacting solely via gravity become entangled, then, according to a simple theorem of quantum mechanics, gravity must quantum. Clearly there are formidable challenges to creating such a system, but remarkably, tabletop technology into the gravitational fields of very small bodies has advanced to the point that such an experiment might be feasible in the next several years. In this talk I will explain the proposal and what it aims to show, highlighting the important ways in which it is theory-laden. (Drawn from joint work with Niels Linnemann and Mike Schneider)*

**22 April** (17:00-19:00 CEST) – **Juliusz Doboszewski **(University of Bonn) – “No ‘No Go’ for LIGO Prediction.” (Watch on YouTube)

Abstract:

*Some authors have claimed that prediction is “essentially impossible” in general relativity. But what is the scope and importance of the formal results underlying the claim? I will discuss this issue in the context of predictions tested in gravitational-wave astronomy, and show how the experimental setup of the LIGO collaboration avoids the “no go” theorem; this sheds new light on some of the more subtle ways in which physicists use general relativity in making predictions.*

**6 May** (17:00-19:00 CEST) – **Vincent Lam** (University of Bern & Grenoble Alpes University) and **Daniele Oriti** (Ludwig Maximilian University of Munich) – “The Laws of Quantum Gravity.” (Watch on YouTube)

Abstract:

*Several approaches in quantum gravity suggest radical revisions of the standard notion of spacetime, and even its disappearance from the fundamental level of description. We discuss traditional conceptions of laws of nature in the light of these new suggestions about spacetime, and why they become untenable, and we indicate some possible ways to characterize the laws of nature in this quantum gravity context. *

**20 May** (17:00-19:00 CEST) – **Carl Hoefer** (ICREA and University of Barcelona) – “Much Ado About Nothing: The Dubious Roles of Points in the Metaphysics of Spacetime.” (Watch on YouTube)

Abstract:

*In a new generation of work on the Hole argument and the right way to formulate substantivalism, the tiniest things of all continue to play an outsized role. In my talk, I will discuss some of the mischiefs that philosophers cause with points, and then offer some reflections on how we might try to re-think the issues. *

**3 June** (17:00-19:00 CEST) – **Eddy Keming Chen** (University of California, San Diego) and **Sheldon Goldstein** (Rutgers University) – “Governing Without A Fundamental Direction of Time: Minimal Primitivism about Laws of Nature.” (Preprint – Watch on YouTube)

Abstract:

*The Great Divide in metaphysical debates about laws of nature is between Humeans who think that laws merely describe the distribution of matter and non-Humeans who think that laws govern it. The metaphysics can place demands on the proper formulations of physical theories. It is sometimes assumed that the governing view requires a fundamental/intrinsic direction of time: to govern, laws must be dynamical, producing later states of the world from earlier ones, in accord with the fundamental direction of time in the universe. In this paper, we propose a minimal primitivism about laws of nature (MinP) according to which there is no such requirement. On our view, laws govern by constraining the physical possibilities. Our view captures the essence of the governing view without taking on extraneous commitments about the direction of time or dynamic production. Moreover, as a version of primitivism, our view requires no reduction/analysis of laws in terms of universals, powers, or dispositions. Our view accommodates several potential candidates for fundamental laws, including the principle of least action, the Past Hypothesis, the Einstein equation of general relativity, and even controversial examples found in the Wheeler-Feynman theory of electrodynamics and retrocausal theories of quantum mechanics. By understanding governing as constraining, non-Humeans who accept MinP have the same freedom to contemplate a wide variety of candidate fundamental laws as Humeans do.*