The particle spectrum and interactions that govern the very early Universe are encoded in maps of the cosmic microwave background and the distribution of galaxies. These signals are a key target for future cosmic surveys, and yet their theoretical foundations from quantum field theory and quantum gravity in accelerating spacetimes remains a work in progress. In this talk, I will review the modern view of inflation that is responsible for this picture and the cosmological correlators it predicts. I will then discuss how new degrees of freedom alter the predictions of inflation and the impact of interactions beyond tree-level. I will conclude with a discussion of the observational prospects for detecting new physics from these cosmological colliders with current and future data, and some new analyses that have been enabled by theory.
