This compares a Milky Way mass galaxy at present day (our “m12i” galaxy), evolving over cosmic time, in column density of neutral hydrogen (left) and partially-ionized oxygen (OVI; right), comparing a model with detailed physics of cooling, star formation, stellar feedback, supernovae, magnetic fields, conduction, viscosity, and more (top), and a model including all of that but also cosmic rays (CRs) accelerated in supernovae, followed fully-explicitly with anisotropic diffusion and streaming, hadronic collisions, resonant Alfven wave interactions, and more (bottom). The extended halo of cosmic rays (shown in the previous movie) provides dominant pressure support at late times. This has a dramatic impact on the phase structure of the CGM. Without CRs, the OVI-absorbing gas is primarily in small, relatively dense “clouds” which come and go (and fragment down to our resolution limit). With CRs, because the dominant pressure is in CRs, diffuse cool/warm gas can be supported against gravity and gas at a wide range of temperatures can co-exist at similar densities, generating a broad/diffuse, volume-filling, low-density OVI phase. Movie made by Cameron Hummels.