Cosmology has moved from its pioneering phase into its middle years, but the end game is not in sight yet. Figure 5 is a schematic view of the basic cosmological parameters, shown in terms of their level of uncertainty. The right hand side of the bar or arrow indicates the level of knowledge that we have now or can anticipate in the near future (for a recent overview, see Turok 1997). Only the Hubble constant is approaching a level of 10% precision, although there is still discordance between results from the conventional chain of of distance indicators and direct techniques (that depend on supernovae, gravitational lensing, and the Sunyaev-Zeldovich effect). Direct measurement of space curvature remains elusive, but the matter density is its proxy in the absence of substantial vacuum energy. The best evidence indicates that the universe cannot be closed by matter, whatever its form. After a series of adjustments to the stellar models, the derived ages of globular clusters have diminished to the point that they can accommodate a flat matter-dominated universe, provided that H0 < 67 km s-1 Mpc-1 (Chaboyer et al. 1998). The issue of the cosmological constant is still unresolved. Finally, we are gradually defining two key attributes of the universe after it begins to form structures - the star formation rate over a Hubble time and the power spectrum of density fluctuations.
The successful measurement of cosmological parameters is leaving us with some deep mysteries. If the cosmological constant can be ruled out, then we need a natural explanation for an open universe without sacrificing the virtues of the inflationary big bang model. If standard inflation is saved with a vacuum energy term, we must explain why its contribution to the density parameter (based on unknown physics) is similar in magnitude to the matter density. Either way, we have to understand why baryons and dark matter particles - two fundamentally distinct microscopic phenomena - occur with roughly similar cosmic density. The invocation of anthropic arguments is merely a distraction as we try to refine our cosmological models. Ignorance can be a virtue; we should embrace it if it leads us to think of new and creative ways to understand the universe.
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| Figure 5. Current estimates of cosmological parameters. The end of the arrows indicate the precision of recent and prospective measurements. The diagram does not account for systematic errors that might affect each of these quantities. |
ACKNOWLEDGMENTS
Thanks go to Mike Disney for illuminating much of our ignorance concerning galaxies, and for coming up with creative ways to counter it. Thanks to Jon Davies and the Local Organizing Committee for arranging a lively and convivial meeting. I acknowledge grant support from the National Science Foundation under AST-9003158 and AST-9617826, and from the International Programs Office of the University of Arizona.