2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/223417All objects in 4D spacetime may in principle travel on null paths in a 5D mani-fold. We use this, together with a change in the extra coordinate and the signature of the metric, to construct a simple model of a classical universe and a quantized particle. There are notable implications for the Weak Equivalence Principle and the cosmological constant, and for astrophysics.General Relativity and Quantum Cosmologytext