  Air showers observed with $E > 10^{20}$ eV pose a problem since protons at
such energies cannot survive a long journey through the 2.7 K microwave
background. It is suggested that they are initiated instead by neutrinos which
become strongly interacting through exchanges of gauge bosons associated with
generation-changing neutral currents, a suggestion which is supported by
calculations in a dualized standard model recently proposed. In turn, the
suggestion bounds the mass of the gauge bosons and gives estimates for the
branching ratios of FCNC s, c, b, and t meson decays which are accessible to
experiments now being planned.
