2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/53693A very basic introduction is given to the rôles of division algebras and the related sphere algebras concerning the structure of space-time in the dimensionalities $D\is 3,4,6$ and $10$, with special emphasis on twistors transformations for light-likeness conditions and Hopf maps, together with some outlook for particle and string theory.10 pages, Goeteborg-ITP-93-43. Inputs: phyzzx, epsf. Uuencoded figure file appendedHigh Energy Physics - Theorytext