2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/11754The geodesics followed by cosmic microwave background (CMB) photons show different behaviours depending on the geometry of space. Namely, the effect of `mixing geodesics' predicts a distinct signature in CMB maps: threshold-independent elongated anisotropy spots in negatively curved geometries. We have found statistically significant sign for spot elongation in the COBE four year maps. This can be a direct indication for the negative curvature of the Universe.Talk given at VIII Marcel Grossmann Meeting (Jerusalem, 1997); to appear in proceedings; Latex 4 pagesAstrophysicstext