 String theory (or its descendant, M-theory) has emerged as a speculative candidate for unifying much of fundamental physics, including quantum mechanics and general relativity. Existing string theories proceed by quantizing classical theories of basic entities that are extended in one or more dimensions of a space that has 6 or 7 tiny compact dimensions in addition to the three spatial dimensions of ordinary geometry. If these additional dimensions are appropriately considered spatial, then it is natural to extend the concepts of  spatial  and  spatiotemporal  separability to encompass them. In that case, processes involving classical strings (or p-branes with \(p \gt 0\)) would count as (spatiotemporally) nonseparable, even though all particles and their properties conform to spatial separability.