Talks this week: Mohapatra, Matarese, Martens, Salimkhani

The Geneva Symmetry Group, Beyond Spacetime, and the Space and Time After Quantum Gravity Project are happy to present a week with four talks, as follows:

Wednesday, 2 May 2018, in Room L208 at 2, Rue De-Candolle:
18:15-19:00 Sonali Mohapatra (University of Sussex): Non-local effective quantum gravity and gravitational waves

19:00-19:45 Vera Matarese (Czech Academy of Sciences): On the tenability of Humeanism in Loop Quantum Gravity

and

Thursday, 3 May 2018, in Room B002 at Uni Bastions:
16:15-17:00 Niels Martens (RWTH Aachen University/Epistemology of the LHC Research Unit): Dark Matter = Modified Gravity? Scrutinising the spacetime-matter distinction through the modified gravity/dark matter lens

17:00-17:45 Kian Salimkhani (University of Bonn): On pregeometry (joint work with Niels Linnemann)

Please find the abstracts, including Einstein score, below.

Anyone who wishes to attend is welcome.

• Wednesday 2 May 2016 at Geneva – DOUBLE HEADER!

Sonali Mohapatra (University of Sussex): Non-local effective quantum gravity and gravitational waves

Abstract: In this talk, I will briefly describe the non-local effective field theory approach to quantum gravity and show some of the predictions such as new modes of gravitational waves. I will then describe some of the open questions in quantum gravity and open the discussion on how to move forward to address the same.

In terms of technical difficulty, this talk rates 5/5

Vera Matarese (Czech Academy of Sciences): On the tenability of Humeanism in Loop Quantum Gravity

Abstract: In this talk, I will discuss whether the results of loop quantum gravity (LQG) constitute a fatal blow for Humeanism. There is at least a prima facie reason for believing so: while Humeanism regards spatiotemporal relations as fundamental, loop quantum gravity describes the fundamental layer of our reality in terms of spin networks, from which spacetime should allegedly emerge. However, the question should be tackled more carefully, not only because there are several ways of addressing this issue depending on whether we focus on the letter or on the spirit of Humeanism, but also because there are different views on what the LQG ontological picture should look like. In my discussion, after reviewing the Humean doctrine and the most important ontological interpretations of LQG, I will home in on and evaluate some strategies that the Humeans could adopt to defend their doctrine and find all of them wanting.

In terms of technical difficulty, this talk rates 2/5

• Thursday 3 May 2016 at Geneva at 16:15– DOUBLE HEADER!

Niels Martens (RWTH Aachen University/Epistemology of the LHC Research Unit): Dark Matter = Modified Gravity? Scrutinising the spacetime-matter distinction through the modified gravity/dark matter lens

Abstract: When applying the laws of gravity to the luminous matter that we observe around us in the universe, one obtains an evolution of that matter which is not empirically adequate—at the scale of galaxies and galaxy clusters as well as at the cosmological scale. We face a dilemma between two options that seem to be obviously distinct: either the matter sector needs to be complemented with non-luminous (i.e. dark) matter (DM), or the gravity/spacetime sector needs to be modified (MG) (or perhaps a bit of both). In this paper, co-authored with Dennis Lehmkuhl, we investigate what criterion, if any, is supposed to conceptually distinguish DM theories from MG theories. In doing so, we not only draw upon literature on the broader distinction between matter on the one hand and spacetime/gravity/geometry on the other, we also move in the other direction by pointing out the implications of the uncovered ambiguities inherent in the DM/MG dichotomy for this broader distinction. More specifically, we compare Khoury and Berezhiani’s Superfluid Dark Matter with Hossenfelder’s Lagrangian formulation of Verlinde’s emergent gravity. We extract from the literature a family of candidates for being necessary and/or sufficient criteria for an object being (dark) matter, as well as a similar family of criteria that determine whether an object is a (modified) spacetime. Both of the above theories score (almost) maximally with respect to both families of criteria: both theories are as much of a dark matter theory as possible, as well as being (almost) as much of a modified spacetime/gravity theory as possible. This case study is a first sign that the distinction between modified gravity and dark matter theories—and by extension the spacetime-matter dichotomy—is much less clear than usually assumed, even before reaching the regime where quantum gravity reigns. This blurring severely undermines the current animosity between dark matter advocates and modified gravity advocates, as well as the substantivalism-relationalism debate (where both camps agree that spacetime and matter are clearly conceptually distinct).

In terms of technical difficulty, this talk rates 4/5 (in parts).

Kian Salimkhani (University of Bonn): On pregeometry (joint work with Niels Linnemann)

Abstract: In this talk, I will investigate the extent to which the dynamical approach to spacetime theories is able to overcome geometry. Famously, the dynamical approach is accused by Norton (2008) of failing to completely reduce geometric spatiotemporal features to matter properties: already setting up the matter fields requires some kind of background structure—some sort of pregeometry. The dynamical approach might be able to evade this criticism as it is primarily concerned with explaining the chronogeometric significance of the metric field, not with explaining how geometry per se emerges from matter properties. Brown and Pooley have responded accordingly; Menon (2018) takes this as conceding too much. After all,—as Norton already noted—it is unnatural to stop the project of explaining geometric properties from matter at the level of metric properties; why not continue? More ambitiously, Menon argues that (physical) geometry per se can indeed be seen as derivative of fields within an algebraic reformulation of the standard fields-on-a-manifold representation. I will first argue that a related issue cannot be circumvented in the context of particle physics’ approaches to GR, and its clarification thus is of central importance not just within interpretational debates regarding GR proper. I will then discuss the issue of pregeometry, and finally stress parallels and disanalogies of these considerations to those concerning the manifold structure in GR.

In terms of technical difficulty, this talk rates 3/5

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About wuthrich

I am a philosopher of physics at the University of Geneva.
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