Callum Jones of the University of Arizona presents on the limits physics places on long-range forces in de Sitter space, the geometry cosmologists use to model a universe with a positive cosmological constant like our own. The talk was given at the kick-off conference for the MPG-IAS-NTU Center, held at the Institute for Advanced Study's Wolfensohn Hall. Jones works through what consistency conditions, drawn from quantum field theory and gravity, say about how strong a new long-range force could be without contradicting known physics or basic principles like unitarity and causality. The discussion sits within the broader program of using de Sitter space as a laboratory for testing quantum gravity conjectures, asking which hypothetical interactions are ruled out and which remain viable. It is a specialist talk aimed at researchers already familiar with effective field theory and cosmological perturbation methods rather than a general audience introduction.