2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34631Three presumably unrelated open questions concerning gravity and the structure of the Universe are here discussed: 1) To which extent is Lorentz invariance an exact symmetry ? 2) What is the equation of state of the Universe ? 3) What is the origin of the so-called Pioneer anomaly ?Latex 8 pages plus moriond.sty. Talk presented at the Rencontres de Moriond, Gravitational Waves and Experimental Gravity, Les Arcs, France, March 2003General Relativity and Quantum Cosmologytext