Condensed Sets and the Solovay Model

Abstract: We exhibit a geometric morphism from the Grothendieck topos representing the Solovay model to the $κ$-pyknotic sets of Barwick-Haine and Clausen-Scholze. We then use the properties of this morphism and automatic continuity in the Solovay model to prove Clausen-Scholze's resolution of the Whitehead problem for discrete condensed abelian groups. We also exhibit an analogous internal $Ext$ computation between locally compact abelian groups in the Solovay model.