SEMINAR      Friday, 18 March 2005 - h. 15:00  Aula Seminari     Y. Srivastava (Dip. di Fisica & INFN, Univ. di Perugia, Italy and Northeastern Univ. Boston, MA, USA) Double Helix for Light Abstract Photons move in (double) helical paths. The photon position obeys a non-commutative geometry and follows a quantum Pythagorean theorem. The distance between two photons in a polarized beam of photons of a given helicity is quantized. A proposed experiment is briefly described.