Venkatessh Ramakrishnan, Violette Impellizzeri, Chi-Kwan Chan, Mariafelicia De Laurentis, Thomas Krichbaum, Andrei Lobanov, Laurent Loinard, Freek Roelofs, Eduardo Ros, Hannah R. Stacey

The observational validation of General Relativity (GR) has been propelled in recent years by recent breakthroughs in Very Long Baseline Interferometry (VLBI) augmented by ALMA. We explore ALMA2040 opportunities to transform these studies through greatly improved sensitivity and a multi-frequency approach. The focus will be on placing most stringent constraints on GR and alternative theories in the strong-gravity regime, and on understanding the formation and launching of relativistic jets.