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current / upcoming
History and Philosophy of Physics Research Seminar
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Tuesdays from 4:15pm to 5:45pm CET.
Online via Zoom. Zoom-links and weekly reminders are announced via hpp@listen.uni-bonn.de; contact nmartens[at]uni-bonn[dot]de to be added to this mailing list. |
Conveners: |
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3 Nov 2020
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Juliusz Doboszewski (University of Bonn)
Kerr black holes as time machines Spinning black holes are now considered to be a well-established feature of our universe. However, some maximal extensions of certain spinning black hole spacetimes (such as the Kerr spacetime) have chronology violating regions. How likely is it, then, that our universe contains chronology violating regions? In this talk, I will discuss whether and to what extent spinning black hole spacetimes could be seen as a time machine in some precise sense, and critically assess a recent claim that time machines (and other forms of time travel to the past in general relativity) are incompatible with the second law of thermodynamics. |
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10 Nov 2020
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Richard Dawid (Stockholm University)
Based on joint work with Casey McCoy (Yonsei University) How postmodern is cosmic inflation? In 2014, Ijjas, Loeb and Steinhardt (ILS) claimed that the paradigm of eternal inflation had left the regime of canonical scientific reasoning (using the pejorative term postmodern inflation). The debate on their paper eventually led to a highly antagonistic and much publicized exchange between ILS and 40 main exponents of inflation in Scientific American. In my talk I will argue that the irreconcilable positions in this debate have genuine philosophical roots. I will sketch a Bayesian analysis of the problem raised by ILS and will argue that acknowledging the role of meta-empirical theory assessment is helpful for identifying the core of the disagreement. |
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17 Nov 2020
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Romain Ruzziconi (TU Wien)
Asymptotic symmetries in gravity and the BMS group in (A)dS I will start this talk by reviewing some aspects of asymptotic symmetries in gauge theories with a focus on General Relativity. I will insist on the deep implications of imposing boundary conditions for the general covariance principle. I will then introduce the notion of asymptotically flat spacetime and define the Bondi-van der Burg-Metzner-Sachs (BMS) group and its various extensions. Afterwards, I will propose a new definition of asymptotically (anti-)de Sitter ((A)dS) spacetime and show that the associated asymptotic symmetry group, called the Λ-BMS group, reduces to one of the extensions of the BMS group in the flat limit. Using the holographic renormalization procedure and a diffeomorphism between Bondi and Fefferman-Graham gauges, I will show that the flat limit is also valid at the level of the phase space. Based on: 1905.00971, 1910.08367, 2004.10769. |
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24 Nov 2020
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Joshua Eisenthal (Caltech & University of Bonn)
Hertz’s Mechanics and a unitary notion of force Heinrich Hertz dedicated the last four years of his life to a systematic reformulation of mechanics. One of the main issues that troubled Hertz in the traditional formulation was a ‘logical obscurity’ in the notion of force. However, it is unclear what this logical obscurity was, hence it is unclear how Hertz took himself to have avoided this obscurity in his own formulation of mechanics. In this paper I will first identify an issue concerning the Newtonian conception of force that lay in the background of Hertz’s concerns. I will argue that a subtle ambiguity in Newton’s original laws of motion led to the development of two different notions of force: a vectorial notion and a variational notion. I will then explore how Hertz employed the mathematical apparatus of differential geometry to arrive at a unitary notion of force, thus avoiding the logical obscurity that lurked in the traditional formulation of mechanics. |
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1 Dec 2020
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Emilie Skulberg (University of Cambridge)
Visual representations of the space around black holes The image of the shadow of a black hole released in April 2019 became an icon in the span of hours. Although this image was historic, if we consider visual representations such as visualisations from simulations, diagrams, and artist impressions, the iconography of black holes dates back decades before the release of imaging based on observation. The first part of my presentation provides a brief overview of this history. The second part accounts for the production of imaging within the Event Horizon Telescope Collaboration, which was behind the April 2019 image. The presentation is based primarily on fieldwork where I have studied the work of the collaboration, an analysis of their publications targeting various audiences, and the study of a collection of black hole imaging from 1973 to 2000. |
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8 Dec 2020
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15 Dec 2020
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Gordon Belot (University of Michigan)
Why we Can’t Know the Shape of Space We will review some classic and contemporary reasons for thinking that it is likely impossible, in a universe like ours, to determine the topology of space via observation. |
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22 Dec 2020
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Sjang ten Hagen (University of Bonn)
Historical Methods in Nineteenth-Century Physics The histories of the historical and the natural sciences have been written largely separately from one another. This is problematic, since it has obscured crucial instances of cross-fertilization between historical and natural-scientific research in the past. In my talk, I discuss a key example of such cross-fertilization: the use of historical methods in physics. In particular, I examine the historically focused work of two prominent German-speaking physicists from the nineteenth century: Johann Christian Poggendorff (1796–1877) and Ernst Mach (1838–1916). Both considered historiography to be a highly valuable tool for the physicist. Their motivations to use this tool, however, were very different. What were these motivations? What did Mach and Poggendorff’s historiography concretely entail? How were their results judged by other physicists, and by historians? And what, finally, does all this suggest about the general relationship between the historical and the natural sciences? |
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12 Jan 2021
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Lydia Patton (Virginia Tech)
Expanding theory testing in general relativity: LIGO and parametrized theories The multiple detections of gravitational waves by LIGO (the Laser Interferometer Gravitational-Wave Observatory), operated by Caltech and MIT, have been acclaimed as confirming Einstein's prediction, a century ago, that gravitational waves propagating as ripples in spacetime would be detected. Yunes and Pretorius (2009) investigate whether LIGO's template-based searches encode fundamental assumptions, especially the assumption that the background theory of general relativity is an accurate description of the phenomena detected in the search. They construct the parametrized post-Einsteinian (ppE) framework in response, which broadens those assumptions and allows for wider testing under more flexible assumptions. Their methods are consistent with work on confirmation and testing found in Carnap (1936), Hempel (1969), and Stein (1992, 1994), with the following principles in common: that confirmation is distinct from testing, and that, counterintuitively, revising a theory's formal basis can make it more broadly empirically testable. These views encourage a method according to which theories can be made abstract, to define families of general structures for the purpose of testing. With the development of the ppE framework and related approaches, multi-messenger astronomy is a catalyst for deep reasoning about the limits and potential of the theoretical framework of general relativity. Based on: https://www.sciencedirect.com/science/article/pii/S1355219818302089 |
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19 Jan 2021
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26 Jan 2021
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Karim Thébault (University of Bristol)
Based on joint work with Sean Gryb (Groningen) Poincaré, Dark Energy, and the Deadly Robots of Krikkit Henri Poincaré, in a strangely neglected passage towards the end of his monumental essay on `Relative and Absolute Motion' (Science and Hypothesis, 1905 Chapter 7), appeals to the idea of a planet entirely secluded form the rest of the universe by clouds to argue that 'as long as nature has secrets' the distinction between constants of nature and constants of motion will remain 'highly arbitrary and always precarious' (p.87). To what extent do such arguments support a relationship between a scientist's epistemic access to different scales and the categorisation of constants? What are the implications of this view for modern cosmology, in particular the interpretation of the cosmological constant and the quantization of gravity? And what does any of this have to do with Robots? In this talk I will attempt to answer these and other related questions. |
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2 Feb 2021
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9 Feb 2021
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Siska de Baerdemaeker (Stockholm University)
The Ultimate Particle Accelerator? Because the LHC’s run is coming to a close in 2035, particle physicists have begun the search for post-LHC probes for physics beyond the standard model (BSM). One option is expanding on a recent trend in particle physics to find early universe constraints on BSM physics. This approach is essentially following through on Zel’dovich adage that the early universe is the “poor man’s accelerator’’, or, in Rocky Kolb’s words, the “ultimate particle accelerator” (1998). The hope is that observations of relics of the early universe somehow contain signatures of BSM physics, or at the very least allow for the exclusion of some proposed BSM physics models. At face value, the early universe probes for BSM physics represent a significant shift in the methodology of high-energy physics away from terrestrial accelerators. In this talk, I investigate what, if any, epistemic shift is associated with that methodological shift. |
2019
Dark Matter / Modified Gravity Conference
Simplicities / Complexities Conference
For more philosophy of physics events taking place in Bonn, please see here.