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**History and Philosophy of Physics Research Seminar**

Time and Place: Tuesdays from 4.15pm to 5:45pm, Institute of Philosophy (Main building of the University of Bonn, Room 1.070).

Schedule for the Winter Semester 2019/2020:

**8.10.2019: Dennis Lehmkuhl (Bonn):**

**“Why integrated history and philosophy of physics? The case of gravity”**

Abstract: I start out with some general remarks about how history of physics, philosophy of physics, and practised physics, relate to one another, and argue that integrated history and philosophy of physics is a particularly fruitful way to understand what’s really going on. I will then draw on my own experiences in working with Albert Einstein’s manuscripts and correspondence in an attempt to understand what he thought gravity is and what general relativity does with gravity, in order to then investigate whether his is the most promising way to understand the theory.

**15.10.2019 Patrick Dürr (Oxford and Bonn):**

**“Unweyling three Mysteries of Nordström Gravity”**

Abstract: The paper re-examines Nordström’s scalar theory of gravity (NG) – arguably the most convincing relativistic theory of gravity before the advent of General Relativity. It exists in two different formulations. In Nordström’s original one (1913), NG appears to describe a scalar gravitational field on Minkowski spacetime. In Einstein and Fokker’s (1914) version, NG seems to be a spacetime theory: It reconceptualises gravitational effects as manifestations of non-Minkowskian inertial structure. Both variants of NG give rise to three contradictory verdicts on the status and validity of fundamental principles: the Weak Equivalence Principle, the existence of gravitational energy, and energy conservation. Given the putative equivalence of both variants of NG, this ambiguity seems paradoxical to the spacetime realist. I’ll proffer a resolution from the perspective of integrable Weyl geometry: The paradoxes rest on the failure to recognise a more apposite spacetime setting for NG.

**22.10.2019 Erik Curiel (MCMP Munich):**

"Kinematics, Dynamics, and the Structure of Theories"

"Kinematics, Dynamics, and the Structure of Theories"

**ABSTRACT: "Every physical theory has (at least) two different forms of mathematical equations to represent its target systems: the dynamical (equations of motion) and the kinematical (kinematical constraints). Kinematical constraints are differentiated from equations of motion by the fact that their particular form is fixed once and for all, irrespective of the interactions the system enters into. By contrast, the particular form of a system's equations of motion depends essentially on the particular interaction the system enters into. All contemporary accounts of the structure and semantics of physical theory treat dynamics, i.e., the equations of motion, as the most important feature of a theory for the purposes of its philosophical analysis. I argue to the contrary that it is the kinematical constraints that determine the structure and empirical content of a physical theory in the most important ways: they function as necessary preconditions for the appropriate application of the theory; they differentiate types of physical systems; they are necessary for the equations of motion to be well posed or even just cogent; and they guide the experimentalist in the design of tools for measurement and observation. It is thus satisfaction of the kinematical constraints that renders meaning to those terms representing a system's physical quantities in the first place, even before one can ask whether or not the system satisfies the theory's equations of motion."**

**29.10.2019 No Seminar**

**5.11.2019: Jamee Elder (Notre Dame and Bonn):**

**“Black hole coalescence: models and measurement”**

ABSTRACT: In this talk I examine the methodology and epistemology of LIGO, with a focus on the role of models and simulations in the experimental process. This includes post-Newtonian approximations, models generated through the effective one-body formalism, and numerical relativity simulations, as well as hybrid models that incorporate aspects of all three approaches. I then present an apparent puzzle concerning the validation of these models: how can we successfully validate these models and simulations through our observations of black holes, given that our observations rely on our having valid models of the systems being observed? I argue that there is a problematic circularity here in how we make inferences about the properties of compact binaries. The problem is particularly acute when we consider these experiments as empirical tests of general relativity. I then consider strategies for responding to this challenge.

12.11.2019 Christian Röken (Bonn):

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12.11.2019 Christian Röken (Bonn):

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**An integral spectral representation of the massive Dirac propagator in the non-extreme Kerr geometry**

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ABSTRACT: We present an integral spectral representation of the massive Dirac propagator in the non-extreme Kerr geometry in horizon-penetrating coordinates, which describes the dynamics of Dirac particles outside and across the event horizon, up to the Cauchy horizon. To this end, we define the Kerr geometry in the Newman–Penrose formalism by means of a regular Carter tetrad in advanced Eddington–Finkelstein-type coordinates and the massive Dirac equation in a chiral Newman–Penrose dyad representation in Hamiltonian form. After showing the essential self-adjointness of the Hamiltonian we compute the resolvent of this operator via the projector onto a finite-dimensional, invariant spectral eigenspace of the angular operator and the radial Green’s matrix stemming from Chandrasekhar’s separation of variables. Then, by applying Stone’s formula to the spectral measure of the Hamiltonian, that is, by expressing the spectral measure in terms of this resolvent, we obtain an explicit integral representation of the Dirac propagator from its formal spectral decomposition.

**Some philosophical questions about the geometrization in General Relativity: approach from an image of nature and image of science**

19.11.2019 Taimara Passero (Sao Paulo and Bonn):

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19.11.2019 Taimara Passero (Sao Paulo and Bonn):

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ABSTRACT:The main aim of this talk is to discuss in which sense we can see the geometrization in General Relativity as an image of nature and/or an image of science. The concepts of image of science and image of nature were proposed by Abrantes (2016). He refers to the former as unsystematic methodologies, and to the latter as unsystematic ontologies that guide the scientific activity. An image of nature has a somewhat diffuse character that incorporates, in a not wholly systematic way, a large number of metaphysical and ontological ideas and intuitions, of which one is not always aware of and whose origin often cannot be retraced. An image of science can include conceptions about the appropriate methods to acquire the scientific knowledge, as well as a set of criteria of theory construction and validation. In both scenarios, the reality is understood from the perspective of the subject. Nevertheless, they differ in as much as one (image of nature) is metaphysical, and the other (image of science) is methodological. From the perspective of the concept of image of nature, geometrization could be seen as a general view of the world: everything would then be viewed as having a geometrical nature. On the other hand, an image of science involves methodological assumptions or criteria for theory construction and validation. These criteria are generally associated with the adoption of cognitive values such as empirical adequacy, simplicity, consistency and predictive power.

ABSTRACT:

**Black to white hole bounces: an integrated history and philosophy of science perspective**

26.11.2019 Juliusz Doboszewski (Bonn):

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26.11.2019 Juliusz Doboszewski (Bonn):

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ABSTRACT:Black to white hole bounces are a class of quantum gravitational scenarios describing late stages of the lifetime of an evaporating black hole, under which presence of repulsive quantum effects leads to tunneling of the black geometry into a time-reversed solution (a white hole). Such bounces provide a form of singularity resolution as well as an answer to the information loss paradox. However, both the remnant proposals and white hole spacetimes are plagued by instabilities. It turns out that there are two distinct arguments for the white hole instability: an early argument based on infinite blueshift, and (arguably more compelling) an argument based on accretion. Some recent claims concerning the stability of white hole remnants address one, but not the other. Attention to this detail implies corrections to the bounce scenario; I will illustrate this claim using an evaporating black hole embedded in a cosmological model with accelerating expansion.

ABSTRACT:

**A unified approach to the relativistic and non-relativistic geodesic principle"**

3.12.2019 Dominic Dold (MPWG Berlin): "

3.12.2019 Dominic Dold (MPWG Berlin): "

**ABSTRACT:**Starting with Einstein himself, there have been several attempts to derive a ‘geodesic principle’ for general relativity (GR), i. e. to prove a theorem that given suitable assumptions, small ‘free bodies’ move along geodesics of a Lorentzian manifold. The celebrated Geroch-Jang theorem belongs to this class of results. Of course, GR is only one kind of curved theory of gravitation, and one might wonder if such proofs also carries over to other gravitational theories. In this talk, I present joint work with Nicholas Teh, showing that – when properly understood – the Geroch-Jang argument indeed suffices to establish a geodesic principle for Newton-Cartan theory.

10.12.2019 Harvey Brown (Oxford):

"What I have learnt from the history of physics"

10.12.2019 Harvey Brown (Oxford):

"What I have learnt from the history of physics"

Abstract: Philosophers of physics seem to be divided as to how important study of the history of physics is for their craft. I will recount how the study of historical episodes in the development of thermal physics, and especially special and general relativity, have helped me understand the nature of these theories.

17.12.2019 Kian Salimkhani (Bonn):

“The dynamical approach to spin-2 gravity”

7.1.2020 Erhard Scholz (Wuppertal):

“Is integrable Weyl geometry useful in phyiscs?”

17.12.2019 Kian Salimkhani (Bonn):

“The dynamical approach to spin-2 gravity”

7.1.2020 Erhard Scholz (Wuppertal):

“Is integrable Weyl geometry useful in phyiscs?”

Abstract: After a short motivation why Weyl geometric gravity matters (EPS argument) and a very short survey on Weyl geometry I want to outline the properties of an intriguing (toy?) example of a scalar field dynamics which can be formulated in Weyl geometric gravity: In the weak field approximation it deflects free fall trajectories and light rays like MOND (provable), has an energy momentum in which the effects on galactic and cluster levels superimpose and may be able to explain the observed dynamics at the level of galaxy clusters (conjectural). The model has a funny Lagrangian density, but details can here only be given as far as the time allows. At the meta level it will be interesting to discuss at least the following points: (i) in the model scale gauge is not only "descriptive fluff" but has observable features, (ii) the scalar field model in question is clearly part of a modified gravity structure (deviation of free fall from Levi-Civita connection); it also has clearly matter like properties (non-negligible contribution to the energy momentum shaping the conformal structure).

14.1.2020 Stephan Hartmann (MCMP Munich):

14.1.2020 Stephan Hartmann (MCMP Munich):

"Scientific Reasoning: The Bayesian Approach"

Abstract: Reasoning and argumentation play an important role in the practice of science. In this talk, I will identify a number of new reasoning and argumentation schemes used in science (such as the No Alternatives Argument and Analogue Simulation) and show how they can be assessed in a normative framework. This will help us to better understand which types or reasoning and argumentation are successful, and which ones need to be improved or discarded. As scientific reasoning and argumentation crucially involve uncertainties, a Bayesian (or probabilistic) approach suggests itself. I will present and develop a general Bayesian framework for the analysis of reasoning and argumentation schemes and illustrate how it can be used to analyze concrete cases from the practice of science.

21.1.2020 Holger Lyre (Magdeburg):

“Structuralism about Parity. Handedness, mirror symmetry, and the metaphysics of space”

28.1.2020 Alexander Blum (MPIWG Berlin):

“The prehistory of of proving non-renormalizability in quantum gravity”

21.1.2020 Holger Lyre (Magdeburg):

“Structuralism about Parity. Handedness, mirror symmetry, and the metaphysics of space”

28.1.2020 Alexander Blum (MPIWG Berlin):

“The prehistory of of proving non-renormalizability in quantum gravity”

For more philosophy of physics events taking place in Bonn, please see here.