The Extreme Universe: Some Views From Here

Forty years have passed since the first Explorer orbiting observatory the 1958 mission used to discover the Van Allen radiation belts outside the atmosphere ushered in the modern age of space science. Even though in situ observations of outer space are still restricted to measurements made within the solar system, we now have access to a wide range of cosmic signals, extending from the well understood microwave photons indicative of the earliest epoch of the universe to those apparently inexplicable ultra-high energy extragalactic cosmic ray particles that are too energetic (up to 50 Joules/each) to have survived passage through a cosmological extent of the pervasive thermal relic radiation field. In this lecture the extremes of cosmic ray physics are discussed within the context of particles having the lowest energy (down to ∼ 10 eV/nucleon) and highest energy (> 10 eV), emphasizing those aspects of astronomy, particularly gamma-ray and x-ray, that appear to be especially revealing for these regimes.