AN ANCIENT REVISITS COSMOLOGY

In this after-dinner speech, a somewhat light-hearted attempt is made to view the observational side of physical cosmology as a subdisciplin e of astrophysics, still in an early stage of sophistication and in ne ed of more theoretical understanding. The theoretical side of cosmolog y, in contrast, has its deep base in general relativity. A major resul t of observational cosmology is that an expansion of the Universe aros e from a singularity some 15 billion years ago. This has had an enormo us impact on the public's view of both astronomy and theology. It plac es on cosmologists an extra responsibility for clear thinking and inte rpretation. Recently, gravitational physics caused another crisis from an unexpected observational result that nonbaryonic matter appears to dominate. Will obtaining information about this massive nonbaryonic c omponent require that astronomers cease to rely on measurement of phot ons? But 40 years ago after radio astronomical techniques uncovered th e high-energy universe, we happily introduced new subfields, with tech niques from physics and engineering still tied to photon detection. An other historical example shows how a subfield of cosmology, big bang n ucleosynthesis, grew in complexity from its spectroscopic astrophysics beginning 40 years ago. Determination of primordial abundances of lig hter nuclei does illuminate conditions in the Big Bang, but the observ ational results faced and overcame many hurdles on the way.