An Account of Advances in Accessing “Discovery Space”

Our knowledge of the origin, early history, and evolution of the Universe, though necessarily based on physical and chemical processes confirmed in the laboratory, inevitably requires verification through direct astronomical observation. The range of potential observations, however, is limited by inherent cosmic features: For electromagnetic radiation, e.g., through erasure of information during early epochs when the cosmic plasma was opaque; for cosmic rays through the Greisen-Zatsepin-Kuz’min cut-off. I will take stock of the progress astronomers have made in accessing “discovery space” --- the range of observations permitted despite such inherent cosmic limits --- to provide an account of the rates at which realizable observations have accumulated over recent decades, while also highlighting work remaining to be done and areas in which progress has been thwarted.