DE / EN
2020/2021
Particle/ astro/ cosmology discussion group
After the online philosophy of dark matter workshop, a group of roughly 20 scholars (incl. physicists, philosophers and historians) has started a regular, global, online discussion group on the history, philosophy and sociology of the intersection between cosmology, astronomy and particle physics, with an initial focus on dark matter. We meet every two weeks on Wednesdays, from 17:00 till 18:00 CEST. Initially we are discussing the dark matter chapters from Peebles’ recent book “Cosmology’s Century”, but eventually we will move on to other/broader topics that are of interest to the group. If you are interested in joining the "Peebles Fan Club", please contact nmartens [at] uni-bonn.de.
History and Philosophy of Physics Research Seminar (Summer)

Time and Place:
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Tuesdays from 16:15 to 17:45 CEST.
Online via Zoom.
Zoom-links and weekly reminders are announced via hpp@listen.uni-bonn.de. Subscribing to this list is possible a) here, b) by sending an empty email to hpp-subscribe@listen.uni-bonn.de, or c) by contacting nmartens[at]uni-bonn[dot]de
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Conveners:
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Prof. Dr. Dennis Lehmkuhl & Dr. Niels Martens
13 April 2021
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Martin Lesourd (Black Hole Initiative, Harvard & Clark University)

What can observers know about their spacetime?

In general relativity (Lorentzian geometry more precisely), one can make this question mathematically precise and study it rigorously. J.Earman, C.Glymour, D.Malament, JB Manchak have all contributed to the question. The most up to date results (before this work) are due to JB Manchak and these seem to suggest a strong sense of epistemic underdetermination, i.e., the answer to the question being `global facts about our spacetime are out of reach in a strong sense' . I'll describe some new results that shed new light on this and I'll state some attractive open questions. 
20 April 2021
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Adam Koberinski (University of Waterloo & University of Bonn)

How effective is inflation?

Inflation is currently a key component of the cosmological model of the early universe. First developed to solve the horizon and flatness problems, its empirical success in predicting the scale-invariant spectrum of inhomogeneities in the cosmic microwave background has cemented inflation as a major component of our understanding of the universe. Standard accounts of inflation involve a scalar field driving exponential expansion of the universe. Coupled with an understanding of our best quantum field theories as effective field theories, many physicists (Weinberg 2008, Cheng et al. 2008) take inflation to be an effective field theory as well.
 
In this talk I will distinguish two notions of effective field theory that are often conflated. The former, loose sense of effective is that the theory is approximate and taken to only be valid in a limited domain, while the second employs the full machinery of the renormalization group, scale separation, and allows one to place quantitative error bounds on calculations made with the theory. I argue that, while inflationꟷalong with many other theoriesꟷis effective in the first sense, it is not in the more robust sense. This has implications for the extent to which we can think of inflation “washing away” the physics of the early universe. If inflation is not an effective field theory in the latter sense, then it is currently a (highly successful) phenomenological model that faces major foundational hurdles to being a useful guide for further inquiry into the early universe. I will end by discussing implications of the argument for exploring alternatives to inflation. In particular, one should prioritize approaches that lead to a fruitful enterprise of early universe cosmology; deviations from the expected behaviour point the way to new physical features relevant to the domain.
27  April 2021
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Shannon Sylvie Abelson (Indiana University, Bloomington)

The fate of TeVeS

The GW 170817 event co-detected by the LIGO and Virgo observatories registered simultaneous arrival times for gravitational waves and electromagnetic radiation emanating from a binary star merger. This detection event has been treated consistently within recent literature (Boran, et al. 2018; Green, et al. 2018; Baker, et al. 2017; Sakstein and Jain 2017; Schmidt 2017) as a crucial test of all alternative theories of gravity which postulate gravitational waves propagate along separate geodesics from electromagnetic spectra—a test such theories fail. These theories are purportedly thereby falsified. This includes relativistic extensions of Milgrom’s Modified Newtonian Dynamics (MOND), perhaps most notably Bekenstein’s Tensor-Vector-Scalar gravity (TeVeS). I critically examine the explicit endorsement of this case as one of falsification by members of the scientific community. While the current state of these theories is dim, it is not clear that recent developments in multimessenger observation can supply a decisive falsification. Rather this evidence should be regarded as merely disconfirmatory. The recommendation of caution regarding philosophical terminology in this case is intended to underscore the importance of having a consistent testing and confirmation methodology. The reliance upon over-simplified historical views from the philosophy of science is likely to be more of a hindrance than a help. 
4 May 2021
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Noah Stemeroff (University of Bonn)

Weyl on the methodology of physical inquiry (or why we can't teach theoretical physics to babies, no matter what Chris Ferrie says)

There is a common belief concerning the nature of scientific knowledge, which suggests that successful physical theories provide an accurate picture of reality. To understand a theory, we simply need to understand this picture and what it says about the world. Against this belief stands the neo-Kantian idealist tradition in the philosophy of science, which suggests that the distinction between ‘theory’ and ‘reality’ is untenable. To the idealist, ‘reality’ is, at least in part, a theoretical construction. In this talk, I will provide an introduction to Cassirer’s neo-Kantian philosophy of science and some aspects of Weyl's more idealistic thought. In particular, I will focus on the way in which Weyl’s account of the role that both history and philosophy play in securing a mathematical harmony in the theoretical construction of reality can serve to support a neo-Kantian challenge to traditional scientific realism. At some point, I will also clarify what all this has to do with the burgeoning theoretical physics for babies literature.
11 May 2021
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Erik Curiel (Munich Center for Mathematical Philosophy & Black Hole Initiative)

Causality, Topology, Affinity, Curvature, Metric

Traditional and popular debates about the metaphysical, physical and conceptual character of different types of structure in spacetime theories such as general relativity tend to focus on the differential manifold and the metric.  There are, however, many different types of structure making up the formalism of such theories, each playing its own peculiar role in making it possible for the integrated whole to be interpreted as a "spacetime".  Those roles, moreover, are not independent of each other: each places non-trivial constraints on the other, and that in a number of ways.  The resulting pattern has more the texture of a web of interlacing, mutually ramifying structures than the clearly stratified and ordered stack of independent layers they are usually depicted as (when attended to at all).  I canvass a number of theorems, constructions and cases exemplifying this glorious mess.  They show clearly that traditional and popular debates such as substantivalism versus relationalism and the dynamical versus the geometrical views are, in the context of general relativity, badly misconceived at best and irremediably incoherent at worst.  The results, facts and observations I discuss reveal new, albeit related, questions, new problems, that deserve their own analysis, investigation and exploration---questions and problems natural to general relativity, arising from its intrinsic formal and conceptual structures, in a way that the standard debates are not, having themselves been imposed by historical contingency or imported from the contexts of other theories where they perhaps had more cogency.​
18 May 2021
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Anna Ijjas (Max Planck Institute for Gravitational Physics)

A new kind of cyclic universe

In this talk, I will discuss how combining intervals of ultra-slow contraction with a (non-singular) classical bounce naturally leads to a novel cyclic theory of the universe in which the Hubble parameter, energy density and temperature oscillate periodically, but the scale factor grows by an exponential factor from one cycle to the next. 
BREAK
1 June 2021
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Robert Rynasiewicz (Johns Hopkins University)

How not to argue that distant simultaneity is conventional

In 1905 Einstein averred that the one-way speed of light in vacuo, and thus the simultaneity of distant events, is a matter of convention. Setting that speed to c in all directions, the principle of relativity together with the light postulate entails that judgments of simultaneity are relative to the choice inertial frames. Reichenbach showed in the early 1920's that the latitude in the original choice of a simultaneity criterion corresponds to the freedom in the choice the parameter ε anywhere between 0 and 1 (exclusively) in the equation

                                             t2 = t1 + ε(t3 – t1)

wherein t1 is the time of departure from point A, t2 the time of arrival and reflection at point B, and t3 the time of return to point A. Subsequently, Grünbaum saw this as defining the region of "topological" simultaneity between future and past light cones, which indicated to him that there is no causally definable hyperplane of simultaneity through their point of intersection. However, Malament showed in 1977 that this is mistaken: the plane that is Minkowski orthogonal to the observer's world line is picked out by causal criteria alone. On this ground, Malament went on to conclude that the criterion for frame relative simultaneity is not conventional.

In this talk, I argue that Grünbaum simply missed Einstein's point. It was for that reason that Malament was able to produce a result in conflict with Grünbaum's contention. But Malament also missed the point, leading him to the false conclusion that frame-relative simultaneity is not conventional. I go on to suggest that in the current divide on the topic, those in the non-conventional camp are typically confused with Grünbaum and Malament on what's at stake in the debate.
8 June 2021
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​Richard Staley (University of Cambridge)

The epistemologist and the history of relational mechanics: Mach, Einstein, Rovelli

Mach’s major contributions to the development of relativity have long seemed to be primarily epistemological - as Einstein avers in his well-known obituary, for example. This paper examines the origins of much of Mach’s work in psychophysics in the 1860s and 70s and his own account of the nature of epistemology from the 1890s onwards to argue instead for a more fluid approach to what has counted as ‘science’ and ‘epistemology’ at different times, while exploring different moments in the history of relational mechanics in the work of Mach, Einstein and Carlo Rovelli.
15 June 2021
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Tiffany Nichols (Harvard University, Dept. of the History of Science & Black Hole Initiative)

The Blueberry Barrens as a Potential Site of Gravitational Wave Detection: Early Understandings of the Role of Land in the Detection of Gravitational Waves

Current literature has unduly collapsed the site selection history of the Laser Gravitational Wave Observatory (LIGO) to a claimed U.S. Congressional decision for LIGO's sites.  My research reveals that the site selection history is more expansive.  By providing an account of LIGO's holistic site selection history, my research shows the importance of land considerations in gravitational wave detection.  This talk will focus on LIGO physicists' initial consideration of a site in the blueberry barrens of Maine during the 1980s.  I will discuss how land features, geological history, and social characteristics of the land became features of the experiment and quest to detect gravitational waves.
22 June 2021
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Kevin Coffey (NYU Abu Dhabi)

Symmetry and Interpretation in Newtonian Gravitation

It has long been recognized that Newtonian gravitation theory exhibits an important symmetry with respect to its inertial structure. Many philosophers of physics have used this fact to conclude that inertial structure within the theory ought to be interpreted as a gauge quantity—a conventional choice without underlying physical significance. This claim originally took shape in the cosmological context, but has now been extended to all models of Newtonian gravitation. In recent years, this argument has also played a role in attempts to show that Newtonian gravitation theory is theoretically equivalent to Newton-Cartan theory, a ‘geometrized’ counterpart to Newtonian gravitation. In my talk I aim to challenge this interpretation of Newtonian gravitation: despite the noted symmetry, I’ll argue that there are good reasons not to interpret its inertial structure as a gauge quantity. In the process, I hope to reveal an unappreciated aspect of the relationship between symmetries and theory interpretation.
29 June 2021
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William L. Vanderburgh (California State University, San Bernardino)

What We Don't Know Could Fill the Universe–And It Does

Given the fact that we have known about the dark matter problem since at least Zwicky 1933, it is rather surprising that we don't yet have a good idea what its solution is. This is even more surprising if you read the popular science press since, dozens of times in recent decades, they have announced that the dark matter mystery has been "solved." Every good idea seems to be quickly shot down and we are left with little but uncertainty. In my talk for the Philosophy of Dark Matter Workshop earlier this spring, I argued that Multi-messenger Astronomy is a model for how we could come to know enough to be scientific realists about dark matter. This paper builds on that one by looking for specific detailed examples of multiple measurement, consilience, multimodal evidence and related evidential concepts in the search for dark matter. It concludes that while there are prospects for fulfilling our hope to discover the nature of dark matter and confirm its role in astrophysics and cosmology, it is still possible that we may never achieve this hope. At this point, we need to wrestle with the possibilities that (1) even if have good reason to think that dark matter exists, it may be a kind of stuff it will be impossible for us ever know and that (2) pursuing knowledge of dark matter might not be worthwhile from the point of view of the costs in time, talent, resources, and lost opportunities to study other things.
6 July 2021
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Panel: Epistemology of Very Large Experiments

Event Horizon Telescope
Jamee Elder (Black Hole Initiative, Harvard & University of Bonn)
Juliusz Doboszewski (University of Bonn & Black Hole Initiative)

LIGO-Virgo 
Jamee Elder (Black Hole Initiative, Harvard & University of Bonn)
Lydia Patton (Virginia Tech)

Large Hadron Collider
Christian Zeitnitz (University of Wuppertal)
Florian Boge (University of Wuppertal)
13 July 2021
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Jeremy Butterfield & Henrique Gomes (University of Cambridge)

​A Noether Hole Argument

​The infamous hole argument---devised by Einstein and revived by Earman & Norton (1987)---has recently found its third wind. The spark that ignited yet another round of debate was Weatherall (2018)'s claim that proper attention to the mathematical structure of general relativity sufficed to disarm the indeterminism implied by the hole argument. One of Weatherall (2018)'s main ideas is to stipulate that, under the right notion of model-isomorphism, points of the manifold necessarily get dragged along with the metric.

While cousins of this reply have appeared in several different attempts to block the indeterminism, we will argue that it cannot encompass all there is to the concept of diffeomorphism symmetry in general relativity. For, by dragging metric and spacetime points together, the effects of a diffeomorphism operation are, in a sense, trivialized. As a result, any idea of symmetry that is associated with this operation cannot secure conservation laws.

The upshot will be that general relativity uses, and needs to use, two distinct notions of identification for the points in the underlying manifolds of symmetry-related models: a notion using a diffeomorphism to drag the metric; and a contrasting notion that individuates spacetime points independently of their metrical relations. But only the latter is non-trivial, in a sense that we describe.
20 July 2021
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Guy Hetzroni (University of Oxford & Utrecht University)
Joint work with James Read

From Spacetime Symmetries to Gravitational Coupling

This paper explores the connection between the gravitational interaction and spacetime symmetries: general covariance on the one hand, and symmetries of the tangent space on the other hand. It is based on understanding general covariance and gauge invariance as a manifestation of one heuristic principle, the methodological equivalence principle, that prescribes the introduction of a new interaction into a theory based on the way it violates an invariance requirement. This way of understanding general covariance can be used to compare general relativity not only with generally covariant formulations of special relativity, but also with gauge theories of gravity that involve non-Riemannian geometrical properties (torsion and non-metricity). Our approach suggests that the coupling prescription of general relativity introduces the minimal structure that at the same time achieves general covariance and also accounts for the preferred role of local inertial frames in non-gravitational dynamics.
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Philosophy of Lambda Workshop
This online workshop focuses on various philosophical aspects of Lambda, i.e. dark energy/ the cosmological constant/ vacuum energy. Nora Mills Boyd and Genco Guralp will discuss experimental aspects. Adam Koberinski, Mike Schneider and David Wallace will debate the cosmological constant problem. ​The workshop will take place on Wednesday the 16th of June 2021, via Zoom. If you are already signed up for the hpp@listen.uni-bonn.de mailing list, there is no need to register for the workshop; you will receive the Zoom-link via the mailing list roughly one week before the workshop. If not, please register via this form by the 8th of June. If you have any questions, please contact the organisers: Juliusz Doboszewski (jdobosze[at]uni-bonn.de) and Niels Martens (nmartens[at]uni-bonn.de).

All times below are in CEST. During the breaks it will be possible to informally chat with the speakers and other participants via the platform Wonder; a link will be sent out in due course.​
14:30-15:30

Chair:
​Niels Martens
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Nora Mills Boyd (Siena College)

Do's and Don'ts from DES: Epistemic challenges in combining constraints from multiple dark energy probes
Abstract
Combining empirical results in an epistemically responsible way requires significant care and attention to details of the provenance of those results. Indeed, the epistemic utility of joint constraints hangs crucially on how they were combined. Cosmologists want to study dark energy by combining data from different probes (the cosmic microwave background, supernovae, gravitational lensing, galaxy clustering, and baryon acoustic oscillations) in order to produce joint constraints on the dark energy equation of state parameter. The details involved in each of these probes are different. They use different instruments, techniques, and modeling assumptions. Until relatively recently, the way that cosmologists have deployed these results together was by processing the data from these diverse probes in parallel and then combining the results at the very end. But, as the Dark Energy Survey (DES) collaboration has pointed out, we have good reason to think that this approach to combining results could be epistemically problematic since the physical processes from which these various results derive are not independent of one another. Therefore, a more sophisticated way to combine them is to take into account correlations between the results from the different probes. Is this second approach enough to ensure that resources and assumptions that have gone into each are not interacting in a way that is problematically affecting the use to which the cosmologists want to put these results? More broadly, what is required in order to combine diverse results in an epistemically responsible way?
Break (15 min)
15:45-16:45

Chair:
​Niels Martens
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Genco Guralp (San Diego State University)

Dark Energy Measurements with Type Ia Supernovae: Mapping the Systematic Uncertainty Terrain
Abstract
​Supernova cosmology played a prominent role in the empirical confirmation of dark energy.  The early work that indicated the existence of dark energy made use of 10s of supernovae (SNe) to establish the accelerating cosmic expansion, which was then interpreted in terms of a positive cosmological constant.  Today,  the available supernova sample contains thousands of objects, and with the advent of the Vera Rubin Observatory and the launch of the Nancy Grace Roman Space Telescope, this statistical sample size will reach unprecedented magnitudes of tens of thousands. With this increase in the sample size, one may expect the systematic uncertainties to dominate the error budget of SNe measurements. In fact, much of the recent work in SNe cosmology is devoted to obtaining a better control on the sources of the systematics that affect the supernova analysis of dark energy.  This is essential, in particular, for the measurement of the w parameter, as indicated in the science goals of the Legacy Survey of Space and Time (LSST) that puts stringent limits on the systematics in the SNe probe. The aim of this talk is to provide a general overview of the sources of systematic error in SNe cosmology and the epistemic strategies the experimentalists recently developed to tackle this issue.  On the basis of this map of the systematic uncertainty terrain, I aim to show that a satisfactory epistemological account of the systematic uncertainty assessment in SNe cosmology requires a detailed examination and classification of distinct forms of modeling and simulation practices that are employed in the uncertainty computations at different levels of analysis.  An important aspect of SNe cosmology is that the underlying physics of supernova explosions are not well understood, and standard data modeling is realized on purely empirical grounds.  This enables experimentalists to continuously improve different aspects of the model of the experiment with the increase in the data supply.  As a result, rather than having a unique aim or function, systematic uncertainty considerations in SNe cosmology play distinct roles that need to be specified at each and every aspect of the experimental activity, including design, data acquisition, modeling, analysis and validation.
Break (15 min)
17:00-19:00

Moderator:
Juliusz Doboszewski
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Debate - The Cosmological Constant Problem

Adam Koberinski (University of Waterloo & University of Bonn)
Mike Schneider (University of Pittsburgh)
David Wallace (University of Pittsburgh)
Philosophy of Dark Matter Workshop
This online workshop is being organised as part of the project "LHC, dark matter & gravity", and will take place on 29-30 March 2021 via Zoom. Click here for further info, incl. (free) registration. The times in the schedule below are in CEST.
History and Philosophy of Physics Research Seminar (Winter)

Time and Place:
Tuesdays from 16:15 to 17:45 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.
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.
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.
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.
24 Nov 2020
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