The embedding of space-time in a higher-dimensional pseudo-Euclidean space is considered as a means of studying the representations of coordinate transformations in curved space-time. To the extent that this approach is valid, the existence of particles belonging to various representations of some internal symmetry group is "predicted" in much the same sense that particles of spin 0, ½, 1, etc. are "predicted" by the structure of representations of the Lorentz group.

DOI:https://doi.org/10.1103/RevModPhys.37.225