Is Cosmology Solved? An Astrophysical Cosmologist's Viewpoint

We have fossil evidence from the thermal background radiation that ouruniverse expanded from a considerably hotter denser state. We have a welldefined and testable description of the expansion, the relativisticFriedmann-Lemaitre model. Its observational successes are impressive but Ithink hardly enough for a convincing scientific case. The lists ofobservational constraints and free hypotheses within the model have similarlengths. The scorecard on the search for concordant measures of the massdensity parameter and the cosmological constant shows that the high densityEinstein-de Sitter model is challenged, but that we cannot choose between lowdensity models with and without a cosmological constant. That is, therelativistic model is not strongly overconstrained, the usual test of a maturetheory. Work in progress will greatly improve the situation and may at lastyield a compelling test. If so, and the relativistic model survives, it willclose one line of research in cosmology: we will know the outlines of whathappened as our universe expanded and cooled from high density. It will not endresearch: some of us will occupy ourselves with the details of how galaxies andother large-scale structures came to be the way they are, others with the issueof what our universe was doing before it was expanding. The former is beingdriven by rapid observational advances. The latter is being driven mainly bytheory, but there are hints of observational guidance.Comment: 13 pages, 3 figures. To be published in PASP as part of the proceedings of the Smithsonian debate, Is Cosmology Solved