2 February 2022

RTG Colloquium - Online (orig. ZARM, University of Bremen)

14:00- 16:30 CET

Schedule:

14:00 - 15:00 Dr. Tessa Baker (Queen Mary University of London): Tests of Gravity with Gravitational Waves

Abstract: The past few years of discoveries in gravitational wave astronomy have had a profound impact on cosmology. In particular, they have triggered a host of new ideas on how to probe the fundamental nature of gravity on large scales. As such, gravitational waves are rapidly becoming a crucial pillar in the long-standing challenge to understand dark energy.
In this talk, I’ll explain the essential phenomenology of gravitational wave propagation outside of General Relativity. We’ll see that gravitational wave sirens — both with and without electromagnetic counterparts — enable us to test very general deviations from GR, via modifications of the propagation speed and luminosity distances of gravitational wave signals. I’ll review some of the key results to date, and also discuss the potential of future gravitational wave detectors to further probe the nature of gravity.

15:00 - 15:30 discussion

15:30 - 16:00 Coffee in the (own) kitchen

16:00 - 17:00 Dr. Melanie Graf (University of Tübingen): Singularity Theorems at Low Regularity

Abstract: The singularity theorems of R. Penrose and S. Hawking from the 1960s show that a spacetime satisfying certain physically reasonable curvature and causality conditions cannot be causal geodesically complete. Despite their great success these classical theorems still have some drawbacks, one of them being that they require smoothness of the metric while in many physical models the metric is less regular. I will first present a summary of the classical theorems and after which I'll give a general overview of the new challenges arising in the statements and proofs of singularity theorems for metrics of lower regularity and review some of the
more recent results and techniques available. For the last part of the talk we'll focus on a version of Hawking's theorem based on a distributional strong energy condition for metrics that are merely continuously differentiable - a regularity where one still has existence but not uniqueness for solutions of the geodesic equation and which represents the current state of the art for an analytic approach.

17:00 - 17:30 discussion