In cosmology, the matter content of the universe is modeled by a relativisitc fluid with linear equation of state. The question of stability of the quiet fluid solutions to this system has been an active field of research in the past decades. While classical solutions are known to break down on a Minkowski background, fluids tend to rapidly stabilize in FLRW spacetimes with positive cosmological constant, driving exponential expansion. In this talk I will discuss recent progress and present a threshold for the stability of homogeneous fluid states, depending on the expansion rate.
This is based on joint work with David Fajman, Maciej Maliborski, Todd Oliynyk and Zoe Wyatt.