Figures of Merit for ELTs

Abstract: In discussing the scientific cases for Extremely Large Telescopes, we are discussing science that may be done in a decade or more. This is a long time to look ahead in any field of human endeavor. Can we make very general statements about the scientific productivity of very large telescopes, that will justify the great investment of both people and money? This paper reviews some of the broad-brush attempts to answer this question based on general information-theory or statistical considerations. It seems clear that the gains with aperture are much bigger for some research areas than others, which raises the pointed question of why we think of ELTs as general-purpose instruments