2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/188441The existence of a new ultraviolet scale $Λ=g M_P$ for effective theories with gravity and U(1) gauge fields has recently been conjectured as a possible criterion for distinguishing parts of the swampland from the string landscape. Here we discuss a possible phenomenological signature of this scale, for electromagnetic fields, in astrophysical observations.6 pages, 2 figures included with epsfig. Essay written for the 2006 Awards for Essays on Gravitation (Gravity Research Foundation), and awarded with "Honorable Mention". To appear in Int. J Mod. Phys. D (December 2006, Special Issue)High Energy Physics - Theorytext