Energy Gaps in a Spacetime Crystal L.P. Horwitz, E.Z. Engelberg (Submitted on 14 Oct 2009) This paper presents an analysis of the band structure of a spacetime potential lattice created by a standing electromagnetic wave. We show that there are energy band gaps. We estimate the effect, and propose a measurement that could confirm the existence of such phenomena. ***** The idea is simple: space time is treated in a non relativistic way, the light cone is a cavity, populated by photons, where the potential inside it is the energy momentum relation. A band gap is found, under reasonable experimental conditions!