The Search for the Source of the Highest Energy Cosmic Rays

Active galaxies and gamma ray bursts are the sources of the highest energy photons detected by astronomical telescopes. We speculate that they may be the sources of the highest energy cosmic rays. This makes them true proton accelerators, where the highest energy photons are the decay products of neutral pions photoproduced when the proton beams interacts with ambient radiation. Neutrinos from the decay of charged pions represent an incontrovertible signature for proton acceleration. A main theme of this talk is that their fluxes can be estimated from the measured gamma ray luminosity by model-independent methods, based on dimensional analysis and textbook particle physics.