Unstable Fluids in Expanding Cosmologies

This seminar from the Harvard CMSA General Relativity series features Elliot Marshal from the School of Mathematics at Monash University discussing instabilities in cosmological fluid models. Explore the FLRW solution, the simplest cosmological model in general relativity that describes a fluid-filled, spatially homogeneous universe. Learn about numerical work on two types of instabilities in non-linearly perturbed FLRW models: Rendall's conjecture regarding models with positive cosmological constant and super-radiative equations of state, and evidence that perturbations of slowly expanding FLRW models typically form shocks in finite time. Discover how these findings contrast with known results for accelerated models where shock formation is suppressed for small perturbations. The presentation examines the limitations of existing stability results and highlights the underlying mechanisms for these cosmological instabilities.