My model for our actual universe is a hypersurface of a round four-sphere. In general, for generic metrics on closed spin three-manifolds, there are no harmonic spinors by anghel-genericvanishingtwisteddiracharmonicspinorsammann-dahl-humbert-surgeryharmonicspinors. Thus for generic hypersurfaces of the four-sphere, the kernel of the Dirac operator is zero, i.e. there are no massless fermions. So I think that the recent discovery of apparently massless Weyl fermions is probably a repetition of the error when neutrinos were considered massless on discovery. I don’t believe that there can be massless fermions in the actual universe.