Cosmological Parameters

The discussion of cosmological parameters used to be a source of embarrassment to cosmologists. Today, measurements of the cosmological parameters are leading the way into the era of precision cosmology. The CMB temperature is measured to four significant figures, T_0=2.7277+/-0.002 K; the Hubble constant is now determined with a reliable error estimate, H_0=(65+/-5) km sec^-1 Mpc^-1; the mass density of baryons is precisely determined by big-bang nucleosynthesis Omega_B = (0.019+/-0.001) h^-2; and the age of the Universe inferred from the ages of the oldest stars is 14+/-1.5 Gyr, which is consistent the expansion age. Further, we have the first full accounting of matter and energy in the Universe, complete with a self consistency check. Expressed as a fraction of the critical density it goes like this: neutrinos, between 0.3% and 15%; stars, between 0.3% and 0.6%; baryons (total), 5+/-0.5%; matter (total),40% +/- 10%; smooth, dark energy, 80% +/- 20%; totaling to the critical density (within the errors).Comment: 27 pages LaTeX with 8 eps figures. To be published in The Proceedings of Particle Physics and the Universe (Cosmo-98), edited by David O. Caldwell (AIP, Woodbury, NY

The Case for Omega_M = 0.33 +/- 0.035

For decades, the determination of the mean density of matter(Omega_M) has been tied to the distribution of light. This has led to a ``bias,'' perhaps as large as a factor of 2, in determining a key cosmological parameter. Recent measurements of the physical properties of clusters, cosmic microwave background (CMB) anisotropy and the power spectrum of mass inhomogeneity now allow a determination of Omega_M without ``visual bias.'' The early data lead to a consistent picture of the matter and baryon densities, with Omega_B = 0.039 +/- 0.0075 and Omega_M = 0.33 +/- 0.035.Comment: 4 ApJ LaTeX. Submitted to Astrophys J Lett. Less provocative title, same conclusion

Cosmology Solved? Quite Possibly!

The discovery of the cosmic microwave background (CMB) in 1964 by Penzias and Wilson led to the establishment of the hot big-bang cosmological model some ten years later. Discoveries made in 1998 may ultimately have as profound an effect on our understanding of the origin and evolution of the Universe. Taken at face value, they confirm the basic tenets of Inflation + Cold Dark Matter, a bold and expansive theory that addresses all the fundamental questions left unanswered by the hot big-bang model and holds that the Universe is flat, slowly moving elementary particles provide the cosmic infrastructure, and quantum fluctuations seeded all the structure seen in the Universe today. Just as it took a decade to establish the hot big-bang model after the discovery of the CMB, it will likely take another ten years to establish the latest addition to the standard cosmology and make the answer to ``Cosmology Solved?'', ``YES!'' Whether or not 1998 proves to be a cosmic milestone, the coming avalanche of high-quality cosmological data promises to make the next twenty years an extremely exciting period for cosmology.Comment: 19 pages LaTeX including 5 eps figures. Presented at Great Debate: Cosmology Solved?, October 4, 1998, Baird Auditorium, Smithsonian Natural History Museum, Washington, DC. To be published in Proc. Astron. Soc. Pacific, February 199