We will be meeting on Thursdays, 16:15-17:45, room B002, Uni Bastions [map: http://www.openstreetmap.org/]

The most up-to-date program:

- 25 February: Welcome, and Augustin Baas: Exploring indeterminism through an assumption of randomness
- 3 March: cancelled (Annual meeting of the German Physical Society)
- 10 March: cancelled (Annual meeting of the GWP in Hannover)
- 17 March: Juliusz Doboszewski: ‘Indeterministic’ spacetimes in classical GR and their disappearance beyond GR: hopes [This talks rates 3.5/5 Einsteins]

Abstract: Classical general relativity is indeterministic in the following sense: there are situations in which the initial value problem does not have unique (up to isometry) solution. In particularly interesting cases, maximal globally hyperbolic spacetime resulting from initial data can be extended in multiple non-equivalent, non-globally hyperbolic ways. I will introduce such spacetimes, show how they relate to the idea of Laplacian determinism, and discuss whether there is a hope for a cure for indeterminism as one moves beyond classical theory: to semi-classical approximations, “discrete” approaches, and canonical quantum gravity. - 24 March: Bohm and hidden variables (Albert, Ch. 7), presented by Lorenzo Cocco
- 31 March: no meeting, Easter vacation
- 7 April: An introduction to special relativity (Michel Janssen, ‘Special relativity’), presented by Benjamin Neeser
- 14 April: Talk by Giuliano Torrengo: The experience of the passage of time

Abstract: It is one of our ordinary beliefs that time passes. And it seems trivial to say that we think this to be so because our experiences tell us so. However, the status of the experience of time passing is a non-trivial matter of debate. Representationalists believe that it is a representational feature of the content of our experience — in the naive version of the theory, something like being red or yellow. Reductionists hold that temporal experiences with qualitative characters, such as experiences as of motion or change, are in some sense responsible for the feeling of the passage of time. Deflationists maintain that there is no distinctive phenomenological character of the passage, but only an intuitive grasp of the ordinary belief that time passes. I will defend what I call the Phenomenal Modifier view. Roughly, according to this view, the feeling of the passage of time should be understood as a modifier of the character and content of experience, just as the blurred, or vivid nature of a visual experience can be seen as modifying the way the experience feels to us. - 21 April: Maudlin, Quantum Non-Locality and Relativity, excerpts, presented by Niels Linnemann
- 28 April: Juliusz Doboszewski: Laplacian indeterminism in spacetimes with boundaries [This talks rates 3/5 Einsteins]
- 5 May: no meeting, Ascension Day
- 12 May: Francesca Vidotto: The covariant dynamics of Loop Quantum Gravity and its consequences

Abstract: Maxwell equations were originally written in long messy pages, now we can get them directly just by combining the Gauss law and Lorentz invariance. Analogously, the complicated Einstein equations can be obtained just by combining Newton law with Lorentz invariance. Loop Quantum Gravity builds on such a simple formulation, that allows to write a quantum theory of gravity as a theory based on Lorentz symmetry where the so-called “simplicity constraint”, that embodies Newton law, is quantized à la Dirac.

By illustrating the basic construction of the covariant dynamics in Loop Quantum Gravity, I will discuss the quantum discreteness naturally appearing, the absence of singularities, the relation with the classical theory and, in particular, the thermodynamical properties of the gravitational field.

Reference: Goffredo Chirco, Hal M. Haggard, Aldo Riello, Carlo Rovelli. Spacetime thermodynamics without hidden degrees of freedom. https://arxiv.org/abs/1401.5262 (12 pages)

- 19 May: Radin Dardashti: Confirmation via Analogue Simulation: What Dumbholes could tell us about Gravity [This talks rates 3/5 Einsteins]

Abstract: Analogue simulation is a novel form of scientific inference with the potential to be confirmatory. This notion is distinct from the modes of analogical reasoning detailed in the literature, and draws inspiration from fluid dynamical ‘dumb hole’ analogues to gravitational black holes. For that case, which is considered in detail, we defend the claim that the phenomena of gravitational Hawking radiation could be confirmed in the case that its counterpart is detected within experiments conducted on diverse realisations of the analogue model. - 26 May: Niels Linnemann: Forking roads towards a theory of quantum gravity: Is general relativity an EFT – or is it not? [This talks rates 2/5 Einsteins]

Abstract: The theory of general relativity (GR) is often rendered – due to its perturbative non-renormalizability – as an effective field theory (EFT). Whether this move is valid, however seems not so clear, especially in light of possibly viable approaches to quantum gravity via canonical quantization (e.g. loop quantum gravity). In this talk, I first motivate a debate on exactly this question, i.e. whether GR is an EFT or not: I point out that settling this issue has direct consequences for the spacetime view of the metric field g – as opposed to the field view – as well as for the general conceptual question of how to approach a theory of quantum gravity. In the main part of the talk, I then consider several positive arguments for the claim that GR is an EFT (e.g. decoherence-based and thermodynamics-based ones), and assess their strengths.

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