In loop quantum gravity, spacetime at the Planck scale is not continuous but discrete. A spin foam is a 2-complex (a network of faces, edges, and vertices) where edges are labeled by SU(2) spin representations j = 0, 1/2, 1, 3/2, … and vertices encode quantum geometry transitions. The partition function Z = Σspin foams ∏f (2jf+1) ∏v {15j}.