It is notoriously hard to calculate the out-of-equilibrium dynamics of many-body quantum systems. While confining particles to one dimension simplifies dynamics in some ways, under most conditions, dynamical solutions have been elusive. A new approximate theoretical approach, generalized hydrodynamics (GHD), makes it easier to model previously intractable dynamics. However, the validity of GHD’s approximations have barely been tested experimentally. I will describe a series of experiments with 1D Bose gases that we take very far from equilibrium by, for instance, making sudden trap changes that lead them to compress 35-fold. We study the evolution of the distribution of rapidities, which are the momenta of the quasiparticles that emerge in these many-body systems, and which we only recently first experimentally observed for gases in equilibrium. These experiments allow us to test the underlying assumptions of GHD in the strong and intermediate coupling regimes. As I will show, we find excellent agreement between our experiments and GHD theory.