  We consider the advantages of and the problems associated with hypotheses to
explain the origin of ulthrahigh energy cosmic rays (UHECR: E > 10 EeV) and the
"trans GZK" cosmic rays (TGZK: E > 100 EeV), both through "old physics"
(acceleration in cosmic sources) and "new physics" (new particles, topological
defects, fat neutrino cross sections, Lorentz invariance violation).
