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, T₀=2.7277+/-0.002 K the Hubble constant is now determined with a reliable error estimate, H₀=(65+/-5) km sec^-1 Mpc^-1 the mass density of baryons is precisely determined by big-bang nucleosynthesis Ω_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 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).