2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36497String theory suggests the existence of gravitational-strength scalar fields ("dilaton" and "moduli") whose couplings to matter violate the equivalence principle. This provides a new motivation for high-precision clock experiments, as well as a generic theoretical framework for analyzing their significance.7 pages, latex, uses moriond.sty, to appear in the Proceedings of the 34th Rencontres de Moriond, "Gravitational Waves and Experimental Gravity", January 1999General Relativity and Quantum Cosmologytext