The fractal Weyl law connects the asymptotic level number with the fractal
dimension of the chaotic repeller. We provide the first test for the fractal
Weyl law for a three-dimensional open scattering system. For the four-sphere
billiard, we investigate the chaotic repeller and discuss the semiclassical
quantization of the system by the method of cycle expansion with symmetry
decomposition. We test the fractal Weyl law for various symmetry subspaces and
sphere-to-sphere separations.Comment: 12 pages, 8 figures, submitted to Phys. Rev.