Warsaw Spacetime Colloquium: Carl Hoefer (20 May on Zoom)

On Friday, 20 May, Carl Hoefer (ICREA and University of Barcelona) will give a talk titled “Much Ado About Nothing: The Dubious Roles of Points in the Metaphysics of Spacetime” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CEST). If you have not registered yet, you can do so here.

The videos of the previous meetings are available on YouTube.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.

Warsaw Spacetime Colloquium: Lam & Oriti (6 May on Zoom)

On Friday, 6 May, Vincent Lam (University of Bern & Grenoble Alpes University) and Daniele Oriti (Ludwig Maximilian University of Munich) will give a talk titled “The Laws of Quantum Gravity” (abstract below).


The meeting will be online on Zoom (17:00-19:00 CEST). If you have not registered yet, you can do so here. The program for this semester is here. The videos of the previous meetings are available on YouTube.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.

Warsaw Spacetime Colloquium: Juliusz Doboszewski (22 April on Zoom)

On Friday, 22 April, Juliusz Doboszewski (University of Bonn) will give a talk titled “No ‘No Go’ for LIGO Prediction” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CEST). If you have not registered yet, you can do so here.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.

Warsaw Spacetime Colloquium: Nick Huggett (8 April on Zoom)

On Friday, 8 April, Nick Huggett (University of Illinois Chicago) will give a talk titled “Gravity meets the Quantum in the Laboratory” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CEST). If you have not registered yet, you can do so here.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.)

Warsaw Spacetime Colloquium: Samuel C. Fletcher (25 March on Zoom)

On Friday, 25 March, Samuel C. Fletcher (University of Minnesota, Twin Cities) will give a talk titled “What Gravitational Waves Really Teach Us about Energy” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CET). If you have not registered yet, you can do so here.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.

Warsaw Spacetime Colloquium: Claudio Calosi (11 March on Zoom)

On Friday, 11 March, Claudio Calosi (University of Geneva) will give a talk titled “Out of all the Indifferences, into One Thing: On Wavefunction Monism” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CET). If you have not registered yet, you can do so here.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.

Warsaw Spacetime Colloquium: John Norton (25 February on Zoom)

On Friday, 25 February, John Norton (University of Pittsburgh) will give a talk titled “Eternal Inflation: When Probabilities Fail” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CET). If you have not registered yet, you can do so here.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.


Warsaw Spacetime Colloquium (online) – New term program

The Philosophy of Physics Group at the Warsaw University of Technology is happy to announce the program of the Warsaw Spacetime Colloquium for the upcoming term:

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

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

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

8 April (17:00-19:00 CEST) – Nick Huggett (University of Illinois at Chicago) – “Gravity Meets the Quantum in the Laboratory.”

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

6 May (17:00-19:00 CEST) – Vincent Lam (University of Bern & Grenoble Alpes University) – TBA

20 May (17:00-19:00 CEST) – Carl Hoefer (ICREA and University of Barcelona) – TBA

3 June (17:00-19:00 CEST) – Michela Massimi (University of Edinburgh) – “Perspectival Modelling: Some Lessons from the History of Nuclear Models around 1930-50.”

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).

Warsaw Spacetime Colloquium: Richard Dawid (21 January on Zoom)

On Friday, 21 January, Richard Dawid (Stockholm University) will give a talk titled “Final but Incomplete – What String Theory May Suggest for 21st Century Physics” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CET). If you have not registered yet, you can do so here.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.

Warsaw Spacetime Colloquium: Elise Crull (7 January on Zoom)

On Friday, 7 January, Elise Crull (City University of New York) will give a talk titled “You’re a Good Man, Harvey Brown: Quantum Rods & Clocks from Decoherence” (abstract below).

The meeting will be online on Zoom (17:00-19:00 CET). If you have not registered yet, you can do so here.

You can address any inquiry to antonio.vassallo@pw.edu.pl.

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.